Electron beam inspection method and apparatus and semiconductor manufacturing method and its manufacturing line utilizing the same

An electron beam inspection method and apparatus. The method includes controlling acceleration voltage of electron beam and electric field on a sample, beam current, beam diameter, image detection rate, image dimensions, precharge, discharge, or a combination of them, exposing an object to the electron beam, detecting in a sensor a physical change generated from the object, and inspecting or measuring the object on the basis of a signal representing the detected physical change. The apparatus includes an electron source (potential E2) for generating an electron beam, a deflector for scanning generated electrons, an objective lens for focusing the electron beam upon the object, a grid (potential E1) disposed between the object and the objective lens, a wafer holder (potential E0) for holding the object, a sensor for detecting generated secondary electrons, a potential controller for controlling the potential E0, E1 and E2, and a storage for storing optimum potential conditions. By changing conditions of an electron optic system such as potential E0, E1 and E2, the acceleration voltage and electric field on the object are controlled. For a material located at least in an upper layer of a plurality of materials forming the object, the secondary electron yield ratio can be made nearly unity and appropriate contrast of an obtained image can be provided with minimized influence of charge up.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and an apparatus for obtaining an 
image or a waveform representing a physical property of an object such as 
a semiconductor wafer with an electron beam, and comparing the image or 
waveform with design information or an image obtained behorehand to judge 
a defect, measure the dimension of a specific place, shape information or 
the fabrication condition of an object such as a semiconductor wafer, or 
display an image, and relates to an inspected wafer and its fabrication 
line in the case where the wafer is the object in the apparatus. 
A conventional method using an electron beam to judge a defect, measure 
shape information or the fabrication condition of an object such as a 
semiconductor wafer, or display an image is described in JP-A-5-258703 
(U.S. Pat. No. 5,502,306), for example. The conventional method includes 
the steps of detecting secondary electrons generated at the time of 
exposure with an electron beam under the same condition, conducting 
scanning with the electron beam, obtaining thereby an image of secondary 
electrons, and judging a defect on the basis of the image. 
It is now assumed that an object is formed by predetermined materials A and 
B. In the case where a certain acceleration voltage Eb of the electron 
beam is used, the secondary electron yield ratio .eta. of the material A 
is largely different from that of the material B. In this case, a 
secondary electron image contrast is obtained, and inspection between the 
material A and the material B is possible. In the case where a specific 
acceleration voltage Ea is used, however, the secondary electron yield 
ratio .eta. of the material A becomes equal to that of the material B. In 
this case, there is little contrast in an obtained secondary electron 
image and the image cannot be observed. In the conventional technique, due 
regard is not paid to such a charge-up phenomenon for each material to be 
observed. 
SUMMARY OF THE INVENTION 
In view of the above described problem, an object of the present invention 
is to provide an electron beam inspection method, and apparatus, for 
reducing the charge-up phenomenon caused when an object is exposed to an 
electron beam, obtaining a high-contrast signal representing a physical 
property by using secondary electrons or back-scattered electrons obtained 
from the object, and making it possible to inspect a minute deffect at 
high speed and with high reliability. 
Another object of the present invention is to provide an electron beam 
inspection method, and apparatus, for adapting the inspection condition to 
the charge-up phenomenon caused when an object is exposed to an electron 
beam, conducting inspection or measurement on the basis of an image signal 
representing a physical property by using secondary electrons or 
back-scattered electrons obtained from the object, and making it possible 
to inspect a minute deffect at high speed and with high reliability. 
Another object of the present invention is to provide an electron beam 
inspection method, and apparatus, for making it possible to inspect minute 
resist patterns and insulator patterns which are apt to be charged, with 
high reliability. 
A further object of the present invention is to provide a semiconductor 
fabrication method and its fabrication line in which minute pattern 
defects on a semiconductor substrate such as a semiconductor wafer are 
inspected to improve the yield. 
In order to achieve the above described objects, in accordance with the 
present invention, an electron beam inspection method includes the steps 
of controlling an acceleration voltage of an electron beam and an electric 
field in neighborhood of an object, exposing the object to the electron 
beam with the controlled acceleration voltage, detecting in a sensor a 
physical change generated from the object in response to the controlled 
electric field, and conducting inspection or measurement of the object on 
the basis of a signal representing the detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam and an electric field in neighborhood of an object, exposing 
the object to the electron beam with the controlled acceleration voltage, 
detecting in a sensor a physical change generated from the object in 
response to the controlled electric field, and displaying a signal 
representing the detected physical change on display means. 
In accordance with the present invention, a electron beam inspection method 
includes the steps of controlling an acceleration voltage of an electron 
beam and an electric field in neighborhood of an object according to a 
kind of a section structure on a surface of the object, exposing the 
object to the electron beam with the controlled acceleration voltage, 
detecting in a sensor a physical change generated from the object in 
response to the controlled electric field, and conducting inspection or 
measurement of the object on the basis of a signal representing the 
detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam and an electric field in neighborhood of an object according 
to at least a kind of a material on a surface of the object, exposing the 
object to the electron beam with the controlled acceleration voltage, 
detecting in a sensor a physical change generated from the object in 
response to the controlled electric field, and conducting inspection or 
measurement of the object on the basis of a signal representing the 
detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam and an electric field in neighborhood of an object according 
to a change of a section structure on a surface of the object, exposing 
the object to the electron beam with the controlled acceleration voltage, 
detecting in a sensor a physical change generated from the object in 
response to the controlled electric field, and conducting inspection or 
measurement of the object on the basis of a signal representing the 
detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam and an electric field in neighborhood of an object according 
to a kind or a change of a section structure on a surface of the object, 
exposing the object to the electron beam with the controlled acceleration 
voltage, detecting in a sensor a physical change generated from the object 
in response to the controlled electric field, and conducting inspection or 
measurement of the object on the basis of a signal representing the 
detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of presetting a proper acceleration voltage of 
an electron beam and a proper electric field in neighborhood of an object 
so as to correspond to a charge-up phenomenon on a surface of an object, 
exposing the object to the electron beam in such a state that the 
acceleration voltage is controlled to become the preset acceleration 
voltage, detecting in a sensor a physical change generated from the object 
in response to the electric field controlled to become the preset electric 
field, and conducting inspection or measurement of the object on the basis 
of a signal representing the detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of presetting a proper acceleration voltage of 
an electron beam and a proper electric field in neighborhood of an object 
so as to correspond to a charge-up phenomenon on a surface of an object 
according to a kind or a change of a section structure on the surface of 
the object, exposing the object to the electron beam in such a state that 
the acceleration voltage is controlled to become the preset acceleration 
voltage, detecting in a sensor a physical change generated from the object 
in response to the electric field controlled to become the preset electric 
field, and conducting inspection or measurement on the object on the basis 
of a signal representing the detected physical change. 
In accordance with the present invention, the charge-up phenomenon is 
grasped as a secondary electron yield efficiency in the electron beam 
inspection method. Furthermore, in accordance with the present invention, 
the acceleration voltage of the electron beam is in the range of 0.3 to 5 
kV, in the electron beam inspection method. In accordance with the present 
invention, the electric field in the neighborhood of the object is 5 kV/mm 
or less, in the electron beam inspection method. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam on a sample, an electric field on the sample, a beam 
current, a beam diameter, an image detection rate (which is the clock 
frequency for reading image signals and which changes the beam current 
density), image dimensions (which is changed by changing the scan rate of 
the electron beam and consequently the beam current density), pre-charge 
(pre-charge on the sample is controlled by blowing an electron shower), 
discharge (discharge on the sample is controlled by blowing an ion 
shower), or a combination of them, exposing an object to the electron 
beam, detecting in a sensor a physical change generated from the object, 
and conducting inspection or measurement of the object on the basis of a 
signal representing the detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of controlling an acceleration voltage of an 
electron beam on a sample, an electric field on the sample, a beam 
current, a beam diameter, an image detection rate (which is the clock 
frequency for reading image signals and which changes the beam current 
density), image dimensions (which is changed by changing the scan rate of 
the electron beam and consequently the beam current density), pre-charge 
(pre-charge on the sample is controlled by blowing an electron shower), 
discharge (discharge on the sample is controlled by blowing an ion 
shower), or a combination of them so as to correspond to a kind or a 
change of a section structure on a surface of an object, exposing the 
object to the electron beam, detecting in a sensor a physical change 
generated from the object, and conducting inspection or measurement of the 
object on the basis of a signal representing the detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing an object to an electron beam, 
detecting in a sensor a physical change generated from the object, and 
conducting inspection or measurement of the object on the basis of a 
signal representing the detected physical change under inspection 
conditions such as inspection conditions (including a judgment standard 
and a measurement standard as well) corresponding to a charge-up 
phenomenon on a surface of the object. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing an object to an electron beam, 
detecting in a sensor a physical change generated from the object, and 
conducting inspection or measurement of the object on the basis of a 
signal representing the detected physical change under inspection 
conditions such as inspection conditions (including a judgment standard 
and a measurement standard as well) corresponding to a charge-up 
phenomenon on a surface of the object according to a kind or a change of a 
section structure on the surface of the object. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing an object to an electron beam, 
detecting in a sensor a physical change generated from the object, and 
extracting a structural feature of the object from a signal representing 
the detected physical change on the basis of a feature extraction 
parameter corresponding to a charge-up phenomenon on a surface of the 
object. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing an object to an electron beam, 
detecting in a sensor a physical change generated from the object, and 
extracting a structural feature of the object from a signal representing 
the detected physical change on the basis of a feature extraction 
parameter corresponding to a charge-up phenomenon on a surface of the 
object according to a kind or a change of a section structure on the 
surface of the object. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of providing a surface of an object with 
pre-charge (i.e., blowing an electron shower) or discharge (i.e., blowing 
an ion shower), exposing the object to an electron beam, detecting in a 
sensor a physical change generated from the object, and conducting 
inspection or measurement of the object on the basis of a signal 
representing the detected physical change. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of providing a surface of an object with 
pre-charge (i.e., blowing an electron shower) or discharge (i.e., blowing 
an ion shower), exposing the object to an electron beam, detecting in a 
sensor a physical change generated from the object, and extracting a 
structural feature on the surface of the object from a signal representing 
the detected physical change. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for controlling an acceleration voltage of 
the electron beam and an electric field in neighborhood of the object, a 
sensor for detecting a physical change generated from the object in 
response to the electric field controlled by the potential control means, 
upon exposure of the object to the electron beam with the acceleration 
voltage controlled by the potential control means, and image processing 
means for conducting inspection or measurement of the object on the basis 
of a signal representing a physical change detected from the sensor. In 
accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for controlling an acceleration voltage of 
the electron beam and an electric field in neighborhood of the object, a 
sensor for detecting a physical change generated from the object in 
response to the electric field controlled by the potential control means, 
upon exposure of the object to the electron beam with the acceleration 
voltage controlled by the potential control means, and display means for 
displaying a signal representing a physical change detected from the 
sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for controlling an acceleration voltage of 
the electron beam and an electric field in neighborhood of the object 
according to a kind or a change of a section structure on a surface of the 
object, a sensor for detecting a physical change generated from the object 
in response to the electric field controlled by the potential control 
means, upon exposure of the object to the electron beam with the 
acceleration voltage controlled by the potential control means, and image 
processing means for conducting inspection or measurement of the object on 
the basis of a signal representing a physical change detected from the 
sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for controlling an acceleration voltage of 
the electron beam and an electric field in neighborhood of the object 
according to a kind or a change of at least a material on a surface of the 
object, a sensor for detecting a physical change generated from the object 
in response to the electric field controlled by the potential control 
means, upon exposure of the object to the electron beam with the 
acceleration voltage controlled by the potential control means, and image 
processing means for conducting inspection or measurement of the object on 
the basis of a signal representing a physical change detected from the 
sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for controlling an acceleration voltage of 
the electron beam and an electric field in neighborhood of the object 
according to a kind or a change of a section structure in an electron beam 
irradiation area on the object, a sensor for detecting a physical change 
generated from the object in response to the electric field controlled by 
the potential control means, upon exposure of the object to the electron 
beam with the acceleration voltage controlled by the potential control 
means, and image processing means for conducting inspection or measurement 
of the object on the basis of a signal representing a physical change 
detected from the sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for effecting control so as to attain a 
proper acceleration voltage of the electron beam and a proper electric 
field in neighborhood of the object so as to correspond to a charge-up 
phenomenon on a surface of the object, a sensor for detecting a physical 
change generated from the object in response to the electric field 
controlled by the potential control means, upon exposure of the object to 
the electron beam with the acceleration voltage controlled by the 
potential control means, and image processing means for conducting 
inspection or measurement of the object on the basis of a signal 
representing a physical change detected from the sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, potential control means for effecting control so as to attain a 
proper acceleration voltage of the electron beam and a proper electric 
field in neighborhood of the object so as to correspond to a charge-up 
phenomenon on a surface of the object according to a kind or a change of a 
section structure on the surface of the object, a sensor for detecting a 
physical change generated from the object in response to the electric 
field controlled by the potential control means, upon exposure of the 
object to the electron beam with the acceleration voltage controlled by 
the potential control means, and image processing means for conducting 
inspection or measurement of the object on the basis of a signal 
representing a physical change detected from the sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, control means for controlling an acceleration voltage of an 
electron beam on a sample, an electric field on the sample, a beam 
current, a beam diameter, an image detection rate, image dimensions, 
pre-charge, discharge or a combination of them, a sensor for detecting a 
physical change generated from the object, upon exposure of the object to 
the electron beam, and image processing means for conducting inspection or 
measurement of the object on the basis of a signal representing a physical 
change detected from the sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, control means for controlling an acceleration voltage of an 
electron beam on a sample, an electric field on the sample, a beam 
current, a beam diameter, an image detection rate, image dimensions, 
pre-charge, dis-charge, or a combination of them so as to correspond to a 
kind or a change of a section structure on a surface of the object, a 
sensor for detecting a physical change generated from the object, upon 
exposure of the object to the electron beam, and image processing means 
for conducting inspection or measurement of the object on the basis of a 
signal representing a physical change detected from the sensor. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, a sensor for detecting a physical change generated from the 
object, upon exposure of the object to the electron beam, inspection 
condition creation means for creating inspection conditions corresponding 
to a charge-up phenomenon on a surface of the object, image processing 
means for conducting inspection or measurement of the object on the basis 
of a signal representing a physical change detected from the sensor, under 
the inspection conditions created by the inspection condition creation 
means. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, a sensor for detecting a physical change generated from the 
object, upon exposure of the object to the electron beam, inspection 
condition creation means for creating inspection conditions corresponding 
to a charge-up phenomenon on a surface of the object according to a kind 
or a change of a section structure on the surface of the object, image 
processing means for conducting inspection or measurement of the object on 
the basis of a signal representing a physical change detected from the 
sensor, under the inspection conditions created by the inspection 
condition creation means. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, a sensor for detecting a physical change generated from the 
object, upon exposure of the object to the electron beam, feature 
extraction parameter creation means for creating a feature extraction 
parameter corresponding to a charge-up phenomenon on a surface of the 
object, and image processing means for extracting a structural feature of 
the object from a signal representing the physical change detected from 
the sensor, on the basis of a feature extraction parameter created by the 
feature extraction parameter creation means. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, means for providing a surface of the object with pre-charge or 
discharge, a sensor for detecting a physical change generated from the 
object, upon exposure of the object to the electron beam, and image 
processing means for conducting inspection or measurement of the object on 
the basis of a signal representing a physical change detected from the 
sensor under inspection conditions. 
In accordance with the present invention, an electron beam inspection 
apparatus includes an electron source, a beam deflector for deflecting an 
electron beam emitted from the electron source, an objective lens for 
focusing the electron beam emitted from the electron source upon an 
object, means for providing a surface of the object with pre-charge or 
discharge, a sensor for detecting a physical change generated from the 
object, upon exposure of the object to the electron beam, and image 
processing means for extracting a structural feature of the object from a 
signal representing the physical change detected from the sensor, on the 
basis of a feature extraction parameter. 
In accordance with the present invention, a semiconductor fabrication line 
includes a plurality of processing systems for processing substrates, a 
control system for controlling the plurality of processing systems, an 
electron beam inspection system for conducting inspection on the basis of 
an image signal, the image signal being obtained by exposing a substrate 
processed by a predetermined processing system to an electron beam, the 
processing systems being controlled by the control system on the basis of 
an inspection result obtained from the electron beam inspection system. 
In accordance with the present invention, a semicondutor fabrication method 
includes the steps of controlling an acceleration voltage of an electron 
beam and an electric field in neighborhood of an object, exposing the 
object to the electron beam with the controlled acceleration voltage, 
detecting in a sensor a physical change generated from a semiconductor 
substrate in response to the controlled electric field, and conducting 
inspection or measurement of the semiconductor substrate on the basis of a 
signal representing the detected physical change and thereby fabricating 
the semiconductor substrate. 
In accordance with the present invention, a semicondutor fabrication method 
includes the steps of controlling an acceleration voltage of an electron 
beam on a sample, an electric field on the sample, a beam current, a beam 
diameter, an image detection rate, image dimensions, pre-charge, 
discharge, or a combination of them, exposing a semiconductor substrate to 
the electron beam, detecting in a sensor a physical change generated from 
the semiconductor substrate, and conducting inspection or measurement of 
the semiconductor substrate on the basis of a signal representing the 
detected physical change and thereby fabricating the semiconductor 
substrate. 
In accordance with the present invention, a semicondutor fabrication method 
includes the steps of exposing a semiconductor substrate to an electron 
beam, detecting in a sensor a physical change generated from the 
semiconductor substrate, and conducting inspection or measurement of the 
semiconductor substrate on the basis of a signal representing the detected 
physical change under inspection conditions corresponding to a charge-up 
phenomenon on a surface of the semiconductor substrate and thereby 
fabricating the semiconductor substrate. 
In accordance with the present invention, a result of the inspection or 
measurement is analyzed and fed back to a predetermined process, in the 
semicondutor fabrication method. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing a sample having a pattern formed on 
a surface thereof to an electron beam, controlling an acceleration voltage 
of the electron beam and an electric field in neighborhood of the sample 
according to the material in an area on the sample exposed to the electron 
beam, detecting secondary electrons or back-scattered electrons generated 
from the sample, and thereby inspecting the pattern on the sample. 
In accordance with the present invention, the acceleration voltage of the 
electron beam is controlled on the basis of a difference between the 
secondary electron yield ratio of the pattern and the secondary electron 
yield ratio of portions other than the pattern, in the electron beam 
inspection method. In accordance with the present invention, the electric 
field in the neighborhood of the sample surface is controlled on the basis 
of the secondary electron yield ratio of the pattern, in the electron beam 
inspection method. 
In accordance with the present invention, an electron beam inspection 
method includes the steps of exposing a sample having a pattern formed on 
a surface thereof to an electron beam, controlling an acceleration voltage 
of the electron beam and an electric field in neighborhood of the sample 
according to the material in an area on the sample exposed to the electron 
beam, counteracting charges stored on the sample surface, detecting 
secondary electrons or back-scattered electrons generated from the sample, 
and displaying an image of the detected secondary electrons or 
back-scattered electrons on a screen, and thereby inspecting the pattern 
on the sample. 
As heretofore described, the present invention makes it possible to reduce 
the charge-up phenomenon caused when an object is exposed to an electron 
beam, obtain a high-contrast signal representing a physical property by 
using secondary electrons or back-scattered electrons obtained from the 
object, and inspect a minute deffect at high speed and with high 
reliability. 
Furthermore, the present invention makes it possible to adapt the 
inspection condition to the charge-up phenomenon caused when an object is 
exposed to an electron beam, conduct inspection or measurement of the 
basis of an image signal representing a physical property by using 
secondary electrons or back-scattered electrons obtained from the object, 
and inspect a minute deffect at high speed and with high reliability. 
Furthermore, the present invention makes it possible to inspect minute 
resist patterns and insulator patterns which are apt to be charged, with 
high reliability. 
Furthermore, the present invention makes it possible to inspect minute 
pattern defects on a semiconductor substrate such as a semiconductor wafer 
with high reliability and improve the yield. 
Furthermore, the present invention makes it possible to inspect minute 
pattern defects on a semiconductor substrate such as a semiconductor wafer 
with high reliability and consequently makes it possible to inspect minute 
pattern defects on a wafer having minute pattern line widths in a 
fabrication line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of a pattern inspection method for inspecting pattern 
dimensions and defects on an object such as a semiconductor wafer by using 
an electron beam and of a fabrication method of a semiconductor wafer 
according to the present invention will now be described by referring to 
drawing. 
The case where a semiconductor wafer is used as an object will be 
described. The same holds true also for other objects such as a photomask, 
thin film multilayer substrate, printed circuit board or TFT substrate. 
By using an electron beam according to the present invention, a pattern on 
an object such as a semiconductor wafer is detected. An embodiment in 
which the pattern of the object is formed by a material A and a material B 
as shown in a sectional view of FIG. 3 will first be described. This 
object forms a solid section structure having a layer made of the material 
A and an upper layer made of the material B. In the case where an object 
thus forming a solid section structure having different materials is 
exposed to an electron beam, there is sometimes little contrast at a 
specific acceleration voltage. This will now be described by referring to 
FIG. 1. FIG. 1 shows the relation between the acceleration voltage E and 
the secondary electron yield ratio .eta. in the case of the material A1 
and the material B2. In the case where the acceleration voltage Eb is 
used, the secondary electron yield ratio of the material A1 is largely 
different from that of the material B2 as evident from FIG. 1. Therefore, 
a secondary electron image obtained from the material A1 and the material 
B2 has sufficient contrast as shown in FIG. 2A. Inspection including 
measurement as well (inspection of the dimension or defect) is thus 
possible. On the contrary, if a specific acceleration voltage Ea is used, 
then the secondary electron yield ratio of the material A1 is equal to 
that of the material B2, and there is little contrast in the secondary 
electron image obtained from the material A1 and the material B2. In this 
case, therefore, a resultant image has little contrast, and inspection 
including measurement as well (inspection of the dimension or defect) 
becomes thus impossible. The specific acceleration voltage Ea differs 
depending upon the material. According to the material of the object, 
therefore, the suitable acceleration voltage differs. 
By using an electron beam according to the present invention, a pattern on 
an object such as a semiconductor wafer is detected. An embodiment in 
which the pattern of the object is formed by a material A3 and a material 
B4 will now be described by referring to FIG. 3, FIGS. 4A, 4B and 4C, FIG. 
5, and FIGS. 6A, 6B, 6C, 6D and 6E. As shown in FIG. 3, an object having a 
solid section structure and including an upper layer made of the material 
A3 (such as a circuit pattern which is conductive) and a lower layer made 
of the material B4 (such as an interlayer insulator which is dielectric) 
is exposed to an electron beam. It is now assumed that such a condition 
that the material B4 is charged up so as to be negative is then satisfied. 
In other words, the secondary electron yield ratio .eta. is unity or less 
(which means that the irradiated electron beam is absorbed and 
consequently the yielded secondary electrons are significantly reduced as 
compared with the irradiation electron beam). In addition, it is also 
assumed that such a condition that the material A3 is charged up so as to 
be positive is satisfied. In other words, the secondary electron yield 
ratio .eta. is unity or more (which means that secondary electrons nearly 
equivalent to the irradiation electron beam are yielded). In the case 
where the degree of charge-up is low, a defect 7 of the material A3 
appears bright in detection, to say nothing of the material A3 as shown in 
FIG. 4A. The material B4 appears dark in detection, and a defect 7 of the 
material A3 forced out into the portion which should originally be the 
material B4 also appears bright in detection. In the case where the 
charge-up is intense, however, there is positive charge-up in the material 
A3 located in the upper layer. Therefore, secondary electrons 6 supplied 
from the defect 7 of the material A3 located in the lower layer are drawn 
toward the material A3 charged up so as to become positive and are not 
detected by a secondary electron detector 16 (11) which will be described 
later by referring to FIGS. 13, 14A through 14C, and 17. As shown in FIGS. 
4B or 4C, therefore, the defect appears small in detection or the defect 
cannot be detected at all. Since information of the inclined portion of 
the material B4 is lost in the same way, the pattern dimension which 
should be detected as shown in FIG. 5A appears small in detection as shown 
in FIG. 5B. 
Furthermore, this phenomenon differs depending upon the speed of ease of 
the charge-up of the object, i.e., the speed of diffusion of electric 
charge charged up so as to become positive or negative. If the ease of 
charge-up is fast, the phenomemon is complicated and the scan direction 
dependency of the electron beam becomes large. Depending upon whether the 
scan direction is X or Y, there occurs a difference in lost information. 
As a result, images as shown in FIGS. 6A and 6B are obtained. When a scan 
is conducted in the X direction, an influence tends to appear in the 
neighborhood of the pattern edge in the X direction. When a scan is 
conducted in the Y direction, an influence tends to appear in the 
neighborhood of the pattern edge in the Y direction. The diffusion differs 
depending upon the conductance of the lower layer pattern (material B). If 
the conductance is large, then the diffusion is extremely fast and the 
ease of the charge-up is fast. 
By using an electron beam according to the present invention, a pattern on 
an object such as a semiconductor wafer is detected. A third embodiment in 
which the pattern of the object is formed by a material A8 and a material 
B9 will now be described by referring to FIGS. 7, 8A, 8B and 8C. As shown 
in FIG. 7, an object having a solid section structure and including a 
lower layer made of the material B8 and an upper layer made of the 
material B4 is exposed to an electron beam 5. It is now assumed that such 
a condition that the material B9 is charged up so as to be positive is 
then satisfied. In other words, the secondary electron yield ratio .eta. 
is unity or more. In addition, it is also assumed that such a condition 
that the material A8 is charged up so as to be negative is satisfied. In 
other words, the secondary electron yield ratio .eta. is unity or less. In 
the case where the degree of charge-up is low, the material A8 appears 
dark in detection as shown in FIG. 8A. The material B9 appears bright in 
detection. In the case where the charge-up is intense, however, an 
electric field is formed under the influence of charge-up. The electric 
field formed in the neighborhood is illustrated. An equipotential line 73 
of 0 V and a negative equipotential line 72 are formed. When the material 
A8 is exposed to the electron beam 5 and consequently secondary electrons 
71 are generated, the secondary electrons 71 are put back by a repulsive 
force from the negative electric field. Therefore, the secondary electrons 
71 cannot arrive at a secondary electron detector 16 (11), and 
consequently information concerning the lower layer is lost. In a portion 
having a dense pattern density as shown in FIG. 8B, therefore, a portion 
which should appear bright in detection appears dark and a suspected 
pattern occurs on a boundary between different pattern densities. 
If charge-up occurs, the secondary electron yield ratio .eta. is changed in 
both cases by its own charge-up. As shown in FIGS. 9A and 9B, therefore, 
an image detected after detection of a plurality of times is changed from 
an image detected at the first time. 
In accordance with the present invention, therefore, charge-up is first 
prevented from occurring as far as possible at least in a pattern located 
in the upper layer (made of the material A) in an object 20. In other 
words, the degree of charge-up is lowered. In addition, from the pattern 
(material A) and a minute spacing of this pattern (material B), a proper 
contrast value .rho. is derived (so as to be high as far as possible). The 
condition of inspection including the measurement is made proper (is 
corrected) so as to detect images under such a condition. This will now be 
described in detail. In the object 20, charge-up is prevented from 
occurring as far as possible at least in the pattern located in the upper 
layer (the material A or B) having a characteristic of second electron 
yield ratio .eta. with respect to an acceleration voltage E for the 
electron beam used to irradiate the materials A and B as shown in FIG. 1. 
(The secondary electron yield ratio .eta. from the pattern (material A or 
B) located in the upper layer is set to a value belonging to a small 
permitted value range around unity.) In addition, it is attempted to 
achieve a proper value of contrast .rho.. (The secondary electron yield 
ratio .eta. from the material B or A located in the lower layer is set to 
a value belonging to a predetermined range such as a range of 0.7 to 1.2 
so as to make the difference from the secondary electron yield ratio of 
the material A or B located in the upper layer the greatest.) Instead of 
an image signal significantly influenced by the charge-up as shown in FIG. 
8B, therefore, an image signal reduced in influence of the charge-up and 
having a proper contrast value .rho. as shown in FIGS. 4A, 5A or 8A can be 
detected by the sensor 11. For preventing charge-up from occurring at 
least in the pattern located in the upper layer (material A or B) of the 
object 20 as far as possible, there can be used a method of reducing the 
quantity of the electron beam stored on the object 20 or a method of 
exposing the object to an electron shower or an ion shower for 
counteraction. 
The method of reducing the quantity of the electron beam stored on the 
object 20 can be implemented by providing proper acceleration voltage 
(E.sub.0 -E.sub.2) for accelerating the electron beam emitted from an 
electron source 14 is provided between the object 20 or voltage providing 
means 19 such as a grid passing the electron beam disposed over the object 
20 and the electron source 14 (which will be described later by referring 
to FIG. 13 and succeeding drawing) and by providing a proper potential 
difference (E.sub.0 -E.sub.1) proportionate to an electric field .alpha. 
on the object between the voltage providing means 19 such as a grid and 
the object 20. However, the phenomenon of charge-up in the pattern located 
in the upper layer changes if the constituent material (material) and 
section structure of the pattern located in the upper layer are changed. 
Therefore, it is necessary to set especially the acceleration voltage E of 
the electron beam used to irradiate the object and the electric field 
.alpha. on the object at proper values with due regard to the constituent 
material (material) and the section structure of the pattern located in 
the upper layer (such as the relation between the constituent material 
[material] of the upper layer and the constituent material [material] of 
the lower layer, and the shape of the pattern [including the pattern width 
and pattern density] and thickness of the pattern). Because the charge-up 
phenomenon changes and consequently the second electron yield ratio .eta. 
changes according to the constituent material (material) and the section 
structure of the pattern located in the upper layer (such as the shape of 
the pattern [including the pattern width and pattern density] and 
thickness of the pattern and the relation with respect to the constituent 
material [material] of the lower layer). In FIG. 1, the secondary electron 
yield ratio .eta. is shown as a function of the acceleration voltage E for 
different materials. 
Furthermore, since the charge-up ease phenomenon (diffusion phenomenon of 
electric charge charged up) occurs in the pattern especially located in 
the upper layer, there occurs a difference in the image signal detected by 
the sensor 11 according to whether the scan direction of the electron beam 
is the X direction or Y direction as shown in FIGS. 6B and 6C. Therefore, 
it is necessary to set especially the acceleration voltage E of the 
electron beam used to irradiate the object and the electric field .alpha. 
on the object at proper values so as to reduce as far as possible the 
difference between an image signal detected by the sensor 11 when the scan 
direction of the electron beam with respect to the object 20 is the X 
direction and that when the scan direction of the electron beam is the Y 
direction. 
Furthermore, in order to inspect the dimension or faults for the pattern 
located in the upper layer, it is necessary to set especially the 
acceleration voltage E of the electron beam used to irradiate the object 
and the electric field .alpha. on the object at proper values so that the 
pattern located in the upper layer may be detected with a proper contrast 
value .rho. as the image signal detected by the sensor 11. 
By the way, the potential difference (E.sub.0 -E.sub.2) represents a 
potential difference between the electron source 14 and the object 20 as 
described later. The potential difference (E.sub.0 -E.sub.2) is the 
acceleration voltage E shown in FIG. 1. By controlling this potential 
difference (E.sub.0 -E.sub.2), i.e., the acceleration voltage E, it is 
possible to change the charge-up phenomenon especially for the pattern 
located in the upper layer (the material A or B), and consequently change 
the secondary electron yield ratio .eta.. In the case where the electric 
field .alpha. is positive, i.e., the secondary electrons are decelerated, 
secondary electrons become difficult to be yielded, resulting in a reduced 
secondary electron yield ratio. On the other hand, in the case where the 
electric field .alpha. is negative, i.e., the secondary electrons are 
accelerated, secondary electrons become easy to be yielded, resulting in 
an increased secondary electron yield ratio .eta.. 
Furthermore, the charge-up phenomenon can be changed and the detected image 
signal can be made proper also by controlling the beam current on the 
object, beam diameter, image detection rate (which is the clock frequency 
for reading image signals and which changes the beam current density), or 
the image dimension (which is changed by changing the scan rate of the 
electron beam and consequently the beam current density). 
As heretofore described, according to the material and the section 
structure of the pattern of the object (such as the shape of the pattern 
[including the pattern width and pattern density] and thickness of the 
pattern and the relation with respect to the constituent material 
[material] of the lower layer), two parameters, for example, (the 
acceleration voltage E of the electron beam used to irradiate the object 
and the electric field .alpha. on the object) are controlled according to 
a predetermined relation. Thereby, the secondary electron yield ratio 
.eta. especially from the pattern located in the upper layer is set in a 
range (approximately unity) permissible with respect to unity. Thereby, 
the charge-up occurring in the pattern located in the upper layer is 
reduced to become less than a predetermined value so as to hardly occur. 
By putting the secondary electron yield ratio .eta. from the material 
located in the lower layer into a predetermined range (such as the range 
of 0.7 to 1.2), the charge-up is reduced as far as possible also for the 
material located in the lower layer. In addition, by making the difference 
in secondary electron yield ratio .eta. between the pattern located in the 
upper layer and the pattern spacing which is not located in the upper 
layer large as far as possible, the contrast .rho. can be made proper. 
Under such a condition that the charge-up is not caused especially for the 
pattern located in the upper layer, therefore, an image having a 
sufficient contrast value can be detected by the sensor 11 and inspection 
of the dimension and defects in the pattern having a finer pattern width 
can be realized with high reliability. In other words, with due regard to 
various factors according to the material and the section structure of the 
pattern of the object (such as the shape of the pattern [including the 
pattern width and pattern density] and thickness of the pattern and the 
relation with respect to the constituent material [material] of the lower 
layer), inspection of the dimension and defects in the fine pattern on the 
semiconductor wafer having a finer pattern width can be realized with high 
reliability. Even in a chip formed on a semiconductor wafer, the material 
and the section structure of the pattern of the object (such as the shape 
of the pattern [including the pattern width and pattern density] and 
thickness of the pattern and the relation with respect to the constituent 
material [material] of the lower layer) change in some cases. Even in a 
chip formed on a semiconductor wafer, therefore, it becomes necessary to 
control the two parameters (the acceleration voltage E of the electron 
beam used to irradiate the object and the electric field .alpha. on the 
object) according to a predetermined relation. If the material and the 
section structure of the surface pattern to be inspected as to the 
dimension and defects change in the object, it is a matter of course that 
it becomes necessary to control the two parameters (the acceleration 
voltage E of the electron beam used to irradiate the object and the 
electric field .alpha. on the object) according to a predetermined 
relation. In any case, it will suffice that the condition of two 
parameters (the acceleration voltage E of the electron beam used to 
irradiate the object and the electric field .alpha. on the object) 
suitable for the material and the section structure of the surface pattern 
can be set until the time immediately before inspecting the surface 
pattern of the object. 
Even if the acceleration voltage E of the electron beam used to irradiate 
the object and the electric field .alpha. on the object are made proper, 
it is impossible to almost get rid of the charge-up phenomenon and the 
charge-up ease phenomenon (diffusion phenomenon of the electric charge 
charged up) especially for the pattern located in the upper layer. In the 
case where a defect inspection, for example, is to be conducted for the 
pattern located in the upper layer on the basis of the image signal 
detected by the sensor 11, therefore, a parameter for extracting a 
structural feature of defects and a defect judgment standard (inspection 
standard) for comparison are determined with due regard to the charge-up 
phenomenon and the charge-up ease phenomenon (diffusion phenomenon of the 
electric charge charged up) for the pattern located in the upper layer. By 
doing so, false detection based upon the charge-up phenomenon and the 
charge-up ease phenomenon for the pattern located in the upper layer can 
be eliminated and the inspection of the dimension and defects in a fine 
pattern on a semiconductor wafer having a finer pattern width can be 
realized with high reliability. If the material and the section shape of 
the pattern of the object (including the pattern width and pattern 
density) are changed, the charge-up phenomenon and the charge-up ease 
phenomenon (diffusion phenomenon of the electric charge charged up) for 
the pattern located in the upper layer also change. Therefore, the 
parameter for extracting the structural feature of defects and the defect 
judgment standard for comparison may be chosen according to the material 
and the section shape of the pattern of the object (including the pattern 
width and pattern density). Alternatively, the charge-up phenomenon and 
the charge-up ease phenomenon (diffusion phenomenon of the electric charge 
charged up) for the pattern located in the upper layer may be detected and 
the parameter for extracting the structural feature of defects and the 
defect judgment standard for comparison may be chosen according to the 
detected charge-up phenomenon and the charge-up ease phenomenon (diffusion 
phenomenon of the electric charge charged up) for the pattern located in 
the upper layer. 
A first embodiment of a system for detecting a pattern on an object such as 
a semiconductor wafer by using an electron beam according to the present 
invention will now be described by referring to FIG. 13. The present 
system includes an electron source 14 having a potential E.sub.2 with 
respect to the ground and generating an electron beam, a beam deflector 15 
for effecting a scan with the electron beam and conducting imaging, an 
objective lens 18 for focusing the electron beam upon an object 20, and a 
potential providing device 19. The potential providing device 19 is 
disposed between the objective lens 18 and the object 20 such as a 
semiconductor wafer. The potential providing device 19 has a potential 
E.sub.1 with respect to the grid and provides a grid or the like with a 
potential. The present system further includes a wafer holder 21. The 
object 20 is mounted on the wafer holder 21. The wafer holder 21 is 
capable of holding the object 20 at a potential E.sub.0 with respect to 
the ground, and has an X-Y stage. The present system further includes a 
sensor 11 for detecting a physical change of secondary electrons generated 
by the object 20 and back-scattered electrons, a height sensor 13 for 
detecting the height of the object 20, and a potential controller 23 for 
controlling the potential values E.sub.0, E.sub.1 and E.sub.2 of 
respective portions which in turn determine the acceleration voltage of 
the electron beam for the object 20. The present system further includes a 
focus controller 22 for controlling the objective lens 18 on the basis of 
the height of the object 20 detected by the height sensor 13 to effect 
focus control, an A/D converter 24 for converting a waveform or image 
signal representing the physical property of the object detected by the 
sensor 11 to a digital signal, and an image processor 25 for conducting 
image processing on the digital signal obtained from the A/D converter 24 
and conducting inspection including the dimension measurement of a pattern 
located on the object. The present system further includes an inspection 
condition corrector 27. On the basis of the digital signal obtained from 
the A/D converter 24 so as to correspond to a process index and an object 
index representing the surface section structure of the object 20, the 
inspection condition corrector 27 corrects inspection conditions (such as 
conditions of the above described two parameters [the acceleration voltage 
E of the electron beam for the object which is given as a potential 
difference (E.sub.0 -E.sub.2), and the electric field .alpha. on the 
object which is given by a nearly proportionate relation as a potential 
difference (E.sub.0 -E.sub.1)] or the charge-up phenomenon to the pattern 
located in the upper layer and charge-up ease phenomenon [diffusion 
phenomenon of the electric charge charged up]). The present system further 
includes an inspection condition setter 28. By specifying a process index 
and an object index representing the surface section structure of the 
object 20, the inspection condition setter 28 stores the inspection 
conditions (such as conditions of the above described two parameters [the 
acceleration voltage E of the electron beam for the object which is given 
as a potential difference (E.sub.0 -E.sub.2), and the electric field 
.alpha. on the object which is given by a nearly proportionate relation as 
a potential difference (E.sub.0 -E.sub.1)] or the charge-up phenomenon to 
the pattern located in the upper layer and charge-up ease phenomenon 
[diffusion phenomenon of the electric charge charged up]) for each group 
of objects (for every objects having the same surface structure). The 
inspection condition setter 28 thus sets inspection conditions. The 
present system further includes a deflection controller 47 for controlling 
the beam deflector 15, a stage controller 50 for controlling the wafer 
holder 21, and a whole controller 26 for controlling the whole of them. 
As the sequence of this system, three ways as shown in FIGS. 14A, 14B and 
14C can be considered. 
In a first scheme, the inspection conditions (such as conditions of the 
above described two parameters [the acceleration voltage E of the electron 
beam for the object which is given as a potential difference (E.sub.0 
-E.sub.2), and the electric field .alpha. on the object which is given by 
a nearly proportionate relation as a potential difference (E.sub.0 
-E.sub.1)]) are set at the time of inspection as shown in FIG. 14A. At 
step 31a, the object 20 is loaded. At step 32a, the object 20 is aligned. 
From the relation of the charge-up phenomenon based on the secondary 
electron yield ratio .eta. which is in turn extracted on the basis of the 
waveform or image signal representing the physical property of the object 
20 detected by the sensor 11, and the charge-up ease phenomenon based upon 
a signal change detected by a plurality of scans of the electron beam, an 
operator then judges and the inspection condition corrector 27 corrects 
and stores the inspection conditions at step 33a. With respect to the 
corrected inspection conditions stored in the inspection condition 
corrector 27, the inspection condition setter 28 stores and sets desired 
inspection conditions at step 34a. At step 35a, the whole controller 26 
controls potential values E.sub.0, E.sub.1 and E.sub.2 of respective 
portions by using the potential controller 23 on the basis of the desired 
inspection conditions preset in the inspection condition setter 28, 
focuses an electron beam yielded from the electron source 14 upon the 
object 20 by using the objective lens 18, causes a scan by using the beam 
deflector 15, detects the physical change of the secondary electrons and 
back-scattered electrons generated by the object 20 by using the sensor 
11, and obtains the waveform or image signal representing the detected 
physical property of the object. On the basis of this signal, an 
inspection of the dimension or defects is conducted in the image processor 
25. At step 36a, the object 20 is unloaded. 
In a second scheme, the inspection conditions (such as the above described 
two parameters [the acceleration voltage E of the electron beam for the 
object which is given as a potential difference (E.sub.0 -E.sub.2), and 
the electric field .alpha. on the object which is given by a nearly 
proportionate relation as a potential difference (E.sub.0 -E.sub.1)]) are 
set before inspection as shown in FIG. 14B. At step 31b, objects having 
different surface structures are loaded beforehand for each group of 
objects such as each lot (i.e., for every objects having the same surface 
structure). At step 32b, the object is aligned. From the relation of the 
charge-up phenomenon based on the secondary electron yield ratio .eta. 
which is extracted on the basis of the waveform or image signal 
representing the physical property of the object 20 detected by the sensor 
11, and the charge-up ease phenomenon based upon a signal change detected 
by a plurality of scans of the electron beam, the inspection condition 
corrector 27 corrects and stores the inspection conditions at step 33b. At 
step 36b, each object 20 is unloaded. At step 31c, an object 20 to be 
subsequently inspected is then loaded. At step 32c, the object is aligned. 
From the corrected inspection conditions for each object having the same 
surface structure stored in the inspection condition corrector 27, the 
inspection condition setter 28 selects, stores and sets desired inspection 
conditions corresponding to the object to be actually inspected at step 
34c. At step 35c, the whole controller 26 controls potential values 
E.sub.0, E.sub.1 and E.sub.2 of respective portions by using the potential 
controller 23 on the basis of the desired inspection conditions preset in 
the inspection condition setter 28, focuses an electron beam yielded from 
the electron source 14 upon the object 20 by using the objective lens 18, 
causes a scan by using the beam deflector 15, detects the physical change 
of the secondary electrons and back-scattered electrons generated by the 
object 20 by using the sensor 11, and obtains the waveform or image signal 
representing the detected physical property of the object. On the basis of 
this signal, an inspection of the dimension or defects is conducted in the 
image processor 25. At step 36c, the object 20 is unloaded. 
A third scheme is shown in FIG. 14C. On the basis of the relation of the 
charge-up phenomenon and the charge-up ease phenomenon based upon the 
secondary electron yield ratio .eta. which can be theoretically or 
empirically calculated from the information of the object, the inspection 
conditions (such as conditions of the above described two parameters [the 
acceleration voltage E of the electron beam for the object which is given 
as a potential difference (E.sub.0 -E.sub.2), and the electric field 
.alpha. on the object which is given by a nearly proportionate relation as 
a potential difference (E.sub.0 -E.sub.1)]) are stored and set in the 
inspection condition setter 28 before inspection at step 37d. At step 31d, 
an object 20 to be subsequently inspected is then loaded. At step 32d, the 
object 20 is aligned. From the inspection conditions stored and set 
beforehand in the inspection condition setter 28, desired inspection 
conditions are stored and set at step 34d. At step 35d, the whole 
controller 26 controls potential values E.sub.0, E.sub.1 and E.sub.2 of 
respective portions by using the potential controller 23 on the basis of 
the preset desired inspection conditions, focuses an electron beam yielded 
from the electron source 14 upon the object 20 by using the objective lens 
18, causes a scan by using the beam deflector 15, detects the physical 
change of the secondary electrons and back-scattered electrons generated 
by the object 20 by using the sensor 11, and obtains the waveform or image 
signal representing the detected physical property of the object. On the 
basis of this signal, an inspection of the dimension or defects is 
conducted in the image processor 25. At step 36d, the object 20 is 
unloaded. The inspection condition setting into the inspection condition 
setter 28 at step 37d may be conducted even after the loading so long as 
it is conducted before the inspection. 
Besides the above described two parameters, the beam current on the object, 
beam diameter, image detection rate (which is the clock frequency for 
reading image signals and which changes the beam current density), or the 
image dimension (which is changed by changing the scan rate of the 
electron beam and consequently the beam current density) can be considered 
as the inspection conditions. 
Correction of the inspection conditions forming components of these 
systems, setting the inspection conditions based on information from the 
object, and setting the corrected inspection conditions will now be 
described. In other words, it suffices that the relations shown in FIGS. 1 
and 10 are derived beforehand. If in the section structure (such as the 
materials A and B) of the object 20 the dependence of the secondary 
electron yield ratio .eta. upon the acceleration voltage (E=E.sub.0 
-E.sub.2) between the electron source 14 and the object 20 and the 
potential difference (E.sub.0 -E.sub.1) proportionate to the electric 
field .alpha. on the object is known, i.e., these relation tables are 
created, then a proper contrast value .rho. (given by a difference between 
the secondary electron yield ratio .eta. from the upper layer pattern and 
the secondary electron yield ratio .eta. from the lower layer pattern) 
indicated by a difference in brightness of image signal between the upper 
layer pattern and the lower layer pattern can be chosen so as to prevent 
the charge-up from occurring with respect to the upper layer pattern 
within a certain permissible range (i.e., so as to attain a small 
permissible value range of the secondary electron yield ratio .eta. from 
the upper layer pattern around unity) and so as to suppress the charge-up 
as far as possible for the lower layer pattern as well (i.e., so as to 
attain a large permissible value range [such as a range of 0.7 to 1.2] of 
the secondary electron yield ratio .eta. from the lower layer pattern 
around unity). 
In other words, a proper acceleration voltage Ec is chosen as shown in FIG. 
11 so as to make large the difference (contrast .rho.) between the 
secondary electron yield ratio .eta. (illustrated by solid lines) from the 
upper layer pattern (material A) and the secondary electron yield ratio 
.eta. (illustrated by broken lines) from the lower layer pattern (material 
B). Thereafter, a potential difference (E.sub.0 -E.sub.1) proportionate to 
the electric field .alpha. on the object is chosen so as to put the 
secondary electron yield ratio .eta. from the upper layer pattern 
(material A) into a small permissible value range around unity. If at that 
time the secondary electron yield ratio .eta. from the lower layer pattern 
(material B) does not come in a large permissible value range around 
unity, then proper inspection conditions can be chosen by finely adjusting 
the acceleration voltage Ec. 
Furthermore, a proper acceleration voltage Ec is chosen as shown in FIG. 12 
so as to make large the difference (contrast .rho.) between the secondary 
electron yield ratio .eta. (illustrated by broken lines) from the upper 
layer pattern (material B) and the secondary electron yield ratio .eta. 
(illustrated by solid lines) from the lower layer pattern (material A). 
Thereafter, a potential difference (E.sub.0 -E.sub.1) proportionate to the 
electric field .alpha. on the object is chosen so as to put the secondary 
electron yield ratio .eta. from the upper layer pattern (material A) into 
a small permissible value range around unity. If at that time the 
secondary electron yield ratio .eta. from the lower layer pattern 
(material A) does not come in a large permissible value range around 
unity, then proper inspection conditions can be chosen by conducting fine 
adjustment so as to cause a shift from the acceleration voltage Ec to an 
acceleration voltage Ed. 
In FIGS. 11 and 12, each of lines of the materials A and B illustrated with 
leader lines represents secondary electron yield ratio values obtained 
when the electric field is 0. Each of lines of the materials A and B which 
are not illustrated with leader lines represents secondary electron yield 
ratio values obtained when the electric field is changed. In other words, 
the secondary electron yield ratio of the upper layer (A in FIG. 11 and B 
in FIG. 12) is kept in the neighborhood of unity. For the purpose of 
keeping the difference in secondary electron yield ratio between the 
materials A and B at an appropriate value, the electric field is changed 
to change the line of secondary electron yield ratio. 
FIG. 15 shows a concrete configuration of an embodiment of the inspection 
condition corrector 27 (27a, 27b) and the inspection condition setter 28. 
Numeral 131 denotes a CPU. Numeral 132 denotes a ROM for storing an 
inspection condition correction processing program. Numeral 133 denotes an 
image memory for storing digital images obtained from the A/D converter 
24. Numeral 134 denotes a RAM for storing various data, corrected 
information of the inspection conditions, and preset inspection 
conditions. Numeral 135 denotes an input device including a keyboard and a 
mouse. Numeral 136 denotes a display device such as a display. Numeral 137 
denotes an external storage device for storing information concerning the 
object such as CAD data. Numeral 138 denotes design information including 
CAD data obtained from the design system. Numerals 139 through 144 denote 
interface (I/F) circuits. Numeral 145 denotes a bus interconnecting the 
components. 
By a command issued by the whole controller 26, respective components shown 
in FIG. 13 are initialized and the stage controller 50 is controlled so as 
to move the object 20 to a predetermined location or a location specified 
by the user. According to a command issued by the whole controller 26, 
predetermined potential values E.sub.0, E.sub.1 and E.sub.2 are set by the 
potential controller 23. A focus position determined by that condition is 
set by the focus controller 22. The object 20 is exposed to an electron 
beam yielded by the electron source 14 via the objective lens 18 while the 
electron beam is being deflected by the beam deflector 15 based on control 
of the deflection controller 47. Physical changes of secondary electrons 
and back-scattered electrons generated in the object 20 are detected by 
the sensor 11. A waveform or image signal representing the physical 
property of the object is thus detected and converted to a digital image 
signal by the A/D converter 24. The inspection condition corrector 27 
stores the digital image signal supplied from the A/D converter 24 in the 
image memory 133 and displays this stored digital image signal on the 
display 136. For an area having a repeated pattern of the displayed 
digital image signal as shown in FIGS. 2, 4, 6, and 8, the user specifies 
a pattern located in the upper layer (material A or B) by using the input 
device 135. On the basis of this specification, the CPU 131 extracts an 
outline of the above described pattern (material A or B) from the detected 
digital image signal, stores the shape of the pattern (material A or B) in 
the external storage device (reference) 137, for example, and stores the 
quantity (such as dose quantity) of the electron beam used to irradiate 
the object 20 as well in the RAM 134, for example, by using the input 
device 135. As for the shape of the pattern (material A or B), it is not 
necessary to extract and derive the outline of the above described pattern 
(material A or B) from the detected digital image signal, and it is 
possible to specify an area on the basis of design information obtained as 
the CAD data 138. Furthermore, since information especially concerning the 
upper layer pattern (such as the shape [including the pattern width and 
pattern spacing] and thickness) is obtained from the CAD data 138, proper 
inspection conditions may be chosen by using this information. 
In order to position a new area which is located on the object 20 and which 
is not subjected to exposure to the electron beam and charge-up, potential 
values E.sub.0, E.sub.1 and E.sub.2 are subjected to change control with a 
constant pitch, for example, in the potential controller 23 for an area of 
each of specified repeated patterns while the stage of the wafer holder 21 
is being scanned on the basis of the stage controller 50. An acceleration 
voltage (E.sub.0 -E.sub.2) between the electron source 14 and the object 
20, and a potential difference (E.sub.0 -E.sub.1) proportionate to the 
electric field .alpha. on the object are thus controlled. A waveform or 
image signal representing the physical change of secondary electrons or 
back-scattered electrons generated from the area of each of specified and 
repeated patterns on the object 20 is detected by the sensor 11, converted 
to a digital image signal by the A/D converter 24, and stored in the image 
memory 133. In addition, data of potential values E.sub.0, E.sub.1 and 
E.sub.2 subjected to change control in the potential controller 23 are 
received via the whole controller 26 and stored in the RAM 134, for 
example. For the digital image signal stored in the image memory 33, the 
CPU 131 calculates an image quality such as a secondary electron yield 
ratio .eta. in a place having an outside shape coinciding with that of a 
pattern (material A or B) stored (registered) in the external storage 
device (reference) 137 and a contrast .rho. of the entire image (given by 
a difference in brightness of digital image signal corresponding to the 
secondary electron yield ratio values .eta. of the materials A and B), and 
stores the calculated image quality in the RAM 134, for example. Out of 
image qualities stored in the RAM 134, for example, the CPU 131 derives 
potential values E.sub.0, E.sub.1 and E.sub.2 existing in a small 
permissible value range of the secondary electron yield ratio .eta. around 
unity (existing in such a state that charge-up is suppressed to the utmost 
for the upper layer pattern) and having the highest image contrast .rho.. 
The CPU 131 stores the derived potential values E.sub.0, E.sub.1 and 
E.sub.2 in the inspection condition storage (the RAM 134 or the external 
storage device 137) as proper inspection conditions. By the way, the 
secondary electron yield ratio .eta. is defined as a ratio of yielded 
secondary electrons to the irradiation electron beam. The quantity of the 
irradiation electron beam (quantity of dose) is stored beforehand in the 
RAM 134, for example, and is already known. From the strength (brightness) 
of a digital image signal correlative to the yielded secondary electrons 
detected by the sensor 11 in a place coinciding with the outside shape of 
a pattern (material A or B), therefore, the CPU 131 can calculate the 
secondary electron yield ratio .eta. as the ratio to the quantity of 
irradiation electron beam. In this way, the secondary electron yield ratio 
.eta. can be calculated as the ratio of the yielded secondary electrons 
detected by the sensor 11 to the quantity of the irradiation electron 
beam. 
Furthermore, the contrast .rho. in the entire image is given by the ratio 
of brightness intensity averaged over the lower layer pattern to 
brightness intensity averaged over the upper layer pattern (in a small 
permissible value of secondary electron yield ratio .eta. around unity). 
In other words, the contrast .rho. of the entire image is given from the 
intensity (brightness) of the digital image signal correlative to the 
yielded secondary electrons detected by the sensor 11 in the upper layer 
pattern (material A) area and its peripheral area (its neighboring area, 
i.e., lower layer pattern area) (material B) as shown in FIG. 8B, for 
example. In this case, the contrast .rho. of the entire image is given as 
the ratio of bright intensity averaged over a plurality of peripheral 
areas (neighboring areas) to dark intensity (in a small permissible value 
range of secondary electron yield ratio .eta. around unity) averaged over 
a plurality of pattern (material A) areas. Since the charge-up is affected 
by the scan of the electron beam as shown in FIGS. 6B and 6C, it is 
necessary to calculate the contrast .rho. of the entire image with due 
regard to this point. In other words, the contrast .rho. of the entire 
image is given as the ratio of bright intensity (in a small permissible 
value range of secondary electron yield ratio .eta. around unity) averaged 
over a portion of a plurality of upper layer pattern areas (material A) 
affected by the scan to dark intensity averaged over a plurality of 
peripheral areas of the upper layer pattern (material A). As a matter of 
course, it is apparent that the contrast .rho. of the portions which are 
included in a plurality of upper layer pattern areas (material A) and 
which are not affected by the scan becomes better. As shown in FIG. 8B or 
FIGS. 6B and 6C, therefore, the CPU 131 can calculate the contrast .rho. 
of the entire image from the intensity (brightness) of a digital image 
signal correlative to the yielded secondary electrons detected by the 
sensor 11 in the pattern (material A) area and its peripheral area 
(neighboring area). 
If this concept is expanded so as to be defined as the sum total of the 
electron beam quantity which is not stored in the object due to 
back-scattering of the electron beam used to irradiate the object 20, and 
irradiation, transmittance, leak, etc. of secondary electrons, then a 
plurality of sensors may be used instead of a single sensor 11 to measure 
terms other than secondary electrons and the measured value may be used in 
the case where the terms other than secondary electrons cannot be 
neglected. 
A method for setting optimum inspection conditions will now be described. A 
two-dimensional image obtained by scanning in the Y direction at low speed 
while repetitively scanning with an electron beam in the X direction at 
high speed is compared with a two-dimensional image obtained by scanning 
in the X direction at low speed while repetitively scanning in the Y 
direction at high speed. The sum .sigma. of pixel contrast difference 
values over the entire image for each image, and the image contrast .rho. 
between the upper layer pattern and the lower layer pattern (i.e., spacing 
between upper layer patterns) in either of the images are calculated. They 
are stored as the image quality. (A small value of the sum .sigma. means 
that charge-up scarcely occurs in such a direction that a scan is effected 
with an electron beam at high speed as shown in FIG. 6A [i.e., it means 
that the secondary electron yield ratio .eta. is approximately unity]. On 
the contrary, a large value of the sum .sigma. means that charge-up occurs 
in such a direction that a scan is effected with an electron beam at high 
speed as shown in FIGS. 6B and 6C.) Among stored image qualities, 
potential values E.sub.0, E.sub.1 and E.sub.2 having the sum .sigma. of 
pixel contrast difference values over the entire image which is equal to 
or less than a fixed permissible value (which means that charge-up 
scarcely occurs as shown in FIG. 6A) and having the highest value of the 
image contrast .rho. may be stored as corrected inspection conditions. 
An alternative method for setting optimum inspection conditions will now be 
described. The same place is scanned with an electron beam to detect an 
image a plurality of times. Those images are compared. The sum .sigma. of 
pixel contrast difference values over the entire image, and the image 
contrast .rho. between the upper layer pattern and the lower layer pattern 
(i.e., spacing between upper layer patterns) in one of the images are 
calculated. They are stored as the image quality. (A small value of the 
sum .sigma. means that charge-up scarcely occurs even if the same place is 
scanned with an electron beam [i.e., it means that the secondary electron 
yield ratio .eta. is approximately unity]). Among stored image qualities, 
potential values E.sub.0, E.sub.1 and E.sub.2 having the sum .sigma. of 
pixel contrast difference values over the entire image which is equal to 
or less than a fixed permissible value (which means that charge-up 
scarcely occurs) and having the highest value of the image contrast .rho. 
or having a minimum change of an average secondary electron yield ratio 
.eta. over the entire image may be stored as corrected inspection 
conditions. 
Instead of setting the optimum inspection conditions wholly in an automatic 
manner, a calculation result of information required for determining the 
inspection conditions or the detected image itself may be presented to an 
operator. From the presented information, the operator determines the 
optimum inspection conditions. Even when this method is used, a similar 
effect can be achieved. The evaluation parameters of the image quality and 
the method for selecting the optimum inspection conditions are not limited 
to those of the above described embodiment. 
The method for setting the inspection conditions on the basis of the 
information of the object will now be described. Beforehand, relations of 
the secondary electron yield ratio .eta. to the acceleration voltage E on 
the object of each material and the electric field .alpha. on the object 
as shown in FIGS. 1 and 10 are derived and stored in the external storage 
device 137 or the RAM 134 of the inspection condition corrector 27 shown 
in FIG. 15. At this time, a waveform or image signal representing a 
physical change of secondary electrons and back-scattered electrons 
generated from areas of each of specified and repeated patterns on the 
object 20 is detected by the sensor 11, converted to a digital image 
signal by the A/D converter 24, and stored in the image memory 133, and 
the secondary electron yield ratio .eta. is calculated from this stored 
digital image signal, as described above with reference to the embodiment. 
Instead of this method, calculation may be effected by using a theoretical 
analysis method. 
So as to correspond to the process index or object index representing the 
surface structure of the object 20, the material (i.e., material of the 
upper layer pattern) located in the upper layer of a section structure 
including a plurality of materials and forming the object (i.e., object to 
be inspected), the material (i.e., material of the lower layer pattern) 
located in the lower layer, the layer thickness and shape of the upper 
layer pattern, and the scan condition of the electron beam are specified 
by using the input device 135. The CPU 131 selects inspection conditions 
(such as potential values E.sub.0, E.sub.1 and E.sub.2) suitable for the 
surface structure of the specified object 20 from the above described 
relation table stored in the external storage device 137 or the RAM 134, 
stores the inspection conditions (such as potential values E.sub.0, 
E.sub.1 and E.sub.2) in the RAM 134 and the like in association with the 
process index or object index representing the surface structure of the 
object 20. The selection of inspection conditions is conducted by looking 
for such conditions that the electron yield ratio .eta. from the material 
located in the upper layer (upper layer pattern) is approximately unity, 
the second electron yield ratio .eta. from the material located in the 
lower layer (lower layer pattern) is in a predetermined range of 0.7 to 
1.2, for example, and has a difference of some degree with respect to the 
electron yield ratio .eta. from the material located in the upper layer 
(upper layer pattern), and deriving potential values E.sub.0, E.sub.1 and 
E.sub.2 associated with such conditions. It is a matter of course that the 
inspection conditions must be chosen with due regard to the layer 
thickness and shape of the upper layer pattern and the scan condition of 
the electron beam. It is because the charge-up characteristic especially 
for the upper layer pattern changes. 
Inspection condition setting in the inspection condition setter 28 will now 
be described. The inspection conditions chosen beforehand in the 
inspection condition corrector 27 are stored in the RAM 134. In the 
inspection condition setter 28, therefore, the process index or object 
index representing the surface structure of the object 20 is inputted by 
using the input device 135. Thereby, corrected inspection condition 
(potential values E.sub.0, E.sub.1 and E.sub.2) can be read out from the 
RAM 134 and set in the potential controller 23 via the whole controller 
26. 
On the basis of the inspection conditions (potential values E.sub.0, 
E.sub.1 and E.sub.2) set in the inspection condition setter 28, the 
potential controller 23 controls the potential E.sub.0 for the object 20, 
the potential E.sub.1 for the voltage providing device 19 for providing 
the electric field .alpha. on the object, and the the potential E.sub.2 
for the electron source 14. The value (E.sub.0 -E.sub.2) represents the 
potential difference from the electron source 14 to the object (sample) 
20, and it is the acceleration voltage E shown in FIG. 1. Furthermore, 
(E.sub.0 -E.sub.1) is proportionate to the electric field .alpha. on the 
object (sample) surface. FIG. 12 shows the secondary electron yield ratio 
.eta. obtained when the electric field .alpha. (proportionate to (E.sub.0 
-E.sub.1)) is changed. If the electric field .alpha. is positive, i.e., 
secondary electrons are decelerated, then the secondary electrons become 
difficult to be yielded, resulting in a decreased secondary electron yield 
ratio .eta.. On the other hand, if the electric field .alpha. is negative, 
i.e., secondary electrons are accelerated, then the secondary electrons 
become easy to be yielded, resulting in an increased secondary electron 
yield ratio .eta.. By controlling these two parameters in the potential 
controller 23 according to a predetermined relation, it is possible to 
attain such a state that the secondary electron yield ratio .eta. is 
approximately unity (i.e., is in a small permissible value range around 
unity) for the material located in the upper layer (upper layer pattern) 
and the charge-up can be thus suppressed to the utmost for the upper layer 
pattern. Thus the image contrast .rho. between the material located in the 
upper layer (upper layer pattern) and the material which is not located in 
the upper layer (lower layer pattern) can be corrected. Under such a 
condition that charge-up is not caused for the upper layer pattern, 
therefore, an image having sufficient contrast can be detected. 
Furthermore, owing to them, minute defects and dimensions can be inspected 
with high reliability in association with the surface structure of the 
object. As a result, it became possible to inspect minute pattern defects 
and dimensions of a wafer having a finer pattern width in a fabrication 
line. Especially by using an electron beam, defects and dimensions in a 
pattern such as an optically transparent oxide film or resist can be 
inspected with high reliability. 
A second embodiment of a system for detecting a pattern on an object such 
as a semiconductor wafer by using an electron beam according to the 
present invention will now be described by referring to FIG. 16. The 
present system (inspection apparatus) includes an electron source 14 for 
generating an electron beam, a beam deflector 15 for effecting a scan with 
the electron beam and conducting imaging, an objective lens (electric 
optics) 18 for focusing the electron beam on a wafer 20 which is the 
object, a potential providing device 19 such as a grid disposed between 
the objective lens 18 and the wafer (object) 20, a wafer holder 21 for 
holding the wafer 20 mounted thereon, a stage 46 for scanning and 
positioning the wafer holder 21, an E.times.B (a device provided with an 
electric field E and a magnetic field B) 17 for collecting secondary 
electrons generated from the surface of the wafer 20 to a secondary 
electron detector 16, a height sensor 13, a focus controller 22 for 
adjusting the focus position of the objective lens 18 on the basis of the 
height information of the wafer surface obtained from the height sensor 
13, a deflection controller 47 for controlling the beam deflector 15 to 
conduct scanning with the electron beam, a potential controller 21 
including a wafer holder potential adjuster 49 for adjusting the potential 
E.sub.0 of the wafer holder 21, a grid potential adjuster 48 for 
controlling the potential E.sub.1 of the voltage providing device 19 such 
as a grid, and an electron source potential adjuster 51 for controlling 
the voltage E.sub.2 of the electron source 14, an A/D converter 24 for 
conducting A/D conversion on a signal supplied from the secondary electron 
detector 16, an image processor 25 including an image memory 52 and an 
image comparator 53 to process the digital image subjected to A/D 
conversion in the A/D converter 24, an inspection condition corrector 27a 
for correcting the inspection conditions on the basis of the digital image 
subjected to A/D conversion, an inspection condition setter 28 for setting 
and storing inspection conditions corrected and chosen by the inspection 
condition corrector 27a, a stage controller 50 for controlling the stage 
46, a whole controller 26 for controlling the whole of them, and an 
inspection vacuum chamber 45 for housing the electron source 14, the beam 
deflector 15, the objective lens (electric optics) 18, the voltage 
providing device 19 such as the grid, and the wafer 20 which is the object 
(sample). 
The sequence of the present system is shown in FIG. 14B. In this scheme, 
inspection conditions are preset before inspection. For each of kinds 
having changed surface section structures, a sample (wafer) 20 is loaded 
(step 31b). (The surface section structure changes from lot to lot and 
from process to process. The surface section structure of the object to be 
inspected might be a resist pattern completed by exposure development, an 
insulator pattern having through-holes connecting the upper layer wiring 
and lower layer wiring between wiring layers, or an insulator pattern, for 
example.) The object is aligned (step 32b). In the inspection condition 
corrector 27a, inspection conditions are then corrected (step 33b). Each 
object is unloaded (step 36b). 
The correction processing of the inspection conditions conducted in the 
inspection condition corrector 27a (step 33b) will now be described. A 
command is issued to the whole controller 26 by the CPU 131. A command 
supplied from the whole controller 26 initializes the components, drives 
and moves the stage 46 to a place specified by the user, and sets the 
focus position of the objective lens 18 by using the focus controller 22 
so as to focus on the height of the sample (wafer) 20 detected by the 
height sensor 13. The CPU 131 displays predetermined menus stored in the 
external storage device 137 and the RAM 134 on the display device 136. Out 
of these menus, the user selects a menu closest to the solid structure 
(section structure) of the sample surface (such as especially the material 
of the upper layer pattern and the material of the lower layer pattern) by 
specifying it with the input device 135 such as a mouse. The CPU 131 sets 
the potential E.sub.2 of the electron source 14, the potential E.sub.1 of 
the voltage providing device 19 such as the grid, and the potential 
E.sub.0 of the wafer holder 21 registered in that menu respectively for 
the electron source potential adjuster 51, the grid potential adjuster 48, 
and the wafer holder potential adjuster 48 included in the potential 
controller 23 via the whole controller 26. By issuing a command via the 
whole controller 26, the CPU 131 sets the focus position determined by the 
inspection conditions by using the focus controller 22. By issuing a 
command via the whole controller 26, the CPU 131 exposes the wafer 20 to 
an electron beam from the electron source 14 via the objective lens 18. 
Secondary electrons generated from the surface of the sample (wafer) 20 
are collected by the E.times.B 17. An image is detected by the secondary 
electron detector 16 and converted to a digital image signal by the A/D 
converter 24. The CPU 131 stores the digital image signal obtained from 
the A/D converter 24 in the image memory 133 temporarily and displays it 
on the display device 135. Out of this displayed digital image, the user 
specifies a pattern having repetition and located in the upper portion by 
using the input device 135 such as a mouse. By extracting the outline of 
that pattern, the shape information of the pattern is calculated and 
stored in the RAM 134 or the external storage device 137. In this way, the 
pattern shape information inclusive of the repetition pitch is information 
depending upon the object to be inspected. Therefore, the pattern shape 
information may be directly obtained from the CAD data 138 and stored in 
the RAM 134 or the external storage device 137. By specification with 
respect to an image detected from the secondary electron detector 16 on 
the basis of the pattern shape information stored in the RAM 134 or the 
external storage device 137, therefore, the secondary electron yield ratio 
.eta. obtained from an area of the upper layer pattern or an area of the 
lower layer pattern can be calculated. 
In other words, by specifying a partial area of a detected image coinciding 
with the pattern shape of the upper layer pattern specified beforehand by 
some means, an image of the upper layer area and an image of the lower 
layer area are discriminated in the image, and the second electron yield 
ratio is specified from the image data. 
In response to a command given from the CPU 131, an area on the wafer 
subjected to exposure to an electron beam is then made a new surface area 
on which charge-up does not occur. For this purpose, the stage controller 
50 is driven and controlled via the whole controller 26. While the stage 
46 having the wafer holder 21 installed thereon is thus being scanned, the 
potential controller 23 is controlled via the whole controller 26 so as to 
change the potential values E.sub.0, E.sub.1 and E.sub.2 with a 
predetermined pitch. In response to a command given via the whole 
controller 26, focus offset determined by the condition is set in the 
focus controller 22. In response to a command given via the whole 
controller 26, the wafer 20 is exposed to an electron beam from the 
electron source 14 via the objective lens 18. According to the changes in 
the potential values E.sub.0, E.sub.2 and E.sub.2, secondary electrons 
generated from the surface area of the repeated upper layer pattern and 
lower layer pattern on the wafer 20 are collected by the E.times.B 17. An 
image is thus detected by the secondary electron detector 16 and converted 
to a digital image signal by the A/D converter 24. According to the 
changes in the potential values E0, E1 and E2 obtained by the A/D 
converter 24, the CPU 131 stores the digital image obtained from the 
surface area of the repeated upper layer pattern and lower layer pattern 
on the wafer 20 in the image memory 133. In the digital image according to 
the changes in the stored potential values E.sub.0, E.sub.2 and E.sub.2, 
it is specified whether the area is an area of the upper layer pattern or 
an area of the lower layer pattern on the basis of the shape information 
of the pattern stored in the RAM 134 or the external storage device 137. 
Thereby, the secondary electron yield ratio .eta. in the area of the upper 
layer pattern and the area of the lower layer pattern according to changes 
of the potential values E.sub.0, E.sub.1 and E.sub.2, and the image 
quality such as the contrast .rho. in the entire image are calculated and 
stored in the external storage device 137 or the like. (The contrast .rho. 
is represented by a difference between the secondary electron yield ratio 
.eta. in the area of the upper layer pattern and the secondary electron 
yield ratio .eta. in the area of the lower layer pattern.) As shown in 
FIGS. 11 and 12, the CPU 131 derives the potential values E.sub.0, E.sub.1 
and E.sub.2 existing in a small permissible value range of the secondary 
electron yield ratio .eta. from the upper layer pattern around unity 
(nearly approximated to unity) (existing in such a state that charge-up is 
suppressed to the utmost for the upper layer pattern), existing in a large 
permissible value range of the secondary electron yield ratio .eta. from 
the lower layer pattern around unity (existing in such a state that 
charge-up is suppressed as far as possible for the lower layer pattern), 
and yielding a proper image contrast value .rho.. The CPU 131 stores the 
derived potential values E.sub.0, E.sub.2 and E.sub.2 in the external 
storage device 137 or the like as inspection conditions (potential values 
E.sub.0, E.sub.1 and E.sub.2) in association with a kind of a change of 
the surface section structure of the object to be inspected (including the 
process). At the time of image detection, the focus controller 22 causes 
follow-up control to a focus position obtained by adding the focus offset 
to the output of the height sensor 13. Furthermore, on the basis of 
actually inspected defect information (especially false detection 
information) obtained from the image comparator 53, for example, included 
in the image processor 25 or the inspection judgment standard (defect 
judgment standard) in the image comparator 53, the CPU 131 calibrates 
(adjusts) the small permissible value range around unity preset for the 
secondary electron yield ratio .eta. obtained from the upper layer pattern 
and the large permissible value range around unity preset for the 
secondary electron yield ratio .eta. obtained from the lower layer 
pattern. Thereby, the CPU 131 amends the inspection conditions (potential 
values E.sub.0, E.sub.1 and E.sub.2). In the inspection condition setter 
28, the inspection conditions (potential values E.sub.0, E.sub.2 and 
E.sub.2) are thus reset. In this way, false detection can be prevented in 
actual inspection conducted in the image processor 25. Because the 
permissible value for the secondary electron yield ratio .eta. relates to 
the inspection judgment standard (defect judgment standard) in the image 
comparator 53. As a matter of course, the CPU 131 may directly calibrate 
the inspection conditions (potential values E.sub.0, E.sub.1 and E.sub.2) 
on the basis of history associated with the surface section structure of 
the object to be inspected concerning the actually inspected defect 
information (especially false detection information) obtained from the 
image comparator 53, for example, included in the image processor 25. 
Furthermore, when calculating the secondary electron yield ratio .eta. 
obtained from the upper layer pattern, or when setting a value in a small 
permissible value range around unity for this secondary electron yield 
ratio .eta., the CPU 131 can select more proper inspection conditions by 
conducting adjustment on the basis of information such as the shape 
(including the pattern width and pattern spacing) and thickness of the 
upper layer pattern obtained from the CAD data 138. 
Inspection processing conducted on the object to be actually inspected 
(wafer) 20 will now be described. Before loading the object to be actually 
inspected (wafer) 20, a kind of a change of the surface section structure 
of the object to be actually inspected (including the process) is inputted 
to the inspection condition setter 28 by using the input device 135. 
Thereby, inspection conditions (potential values E.sub.0, E.sub.1 and 
E.sub.2) corresponding to the object to be actually inspected stored in 
the external storage device 137 are chosen, and set and stored in the RAM 
134. Subsequently, the object to be actually inspected (wafer) 20 is 
loaded on the basis of a command issued by the whole controller 26 (step 
31c). Alignment is conducted (step 32c). In accordance with inspection 
conditions (potential values E.sub.0, E.sub.1 and E.sub.2) corresponding 
to the kind of the object to be actually inspected (variety and process of 
the wafer) which is set and stored beforehand in the RAM 134 of the 
inspection condition setter 28, the electron source potential adjuster 51, 
the grid potential adjuster 48, and the wafer holder potential adjuster 48 
forming the potential controller 23 are controlled so as to obtain the 
potential values E.sub.0, E.sub.1 and E.sub.2 (step 34c). The focus offset 
determined by the conditions is set by the focus controller 22. After 
setting, the stage 46 is driven and run in the Y direction at a constant 
speed under the control of the stage controller 50 on the basis of a 
command given from the whole controller 26. While the stage 46 is being 
thus run, scanning is repetitively conducted in the X direction at high 
speed with the electron beam supplied from the electron source 14 by using 
the beam deflector 15 under the control of the deflection controller 47. 
Secondary electrons obtained from the surface of the object 20 to be 
inspected are collected into the secondary electron detector 16 by the 
E.times.B 17. Two-dimensional secondary electron images are consecutively 
detected by the secondary electron detector 16, and converted to 
two-dimensional digital secondary electron image signals by the A/D 
converter 24. The two-dimensional digital secondary electron image signals 
are stored in the image memory 52 included in the image processor 25. 
Among detected two-dimensional digital secondary electron image signals 
and two-dimensional digital secondary electron image signals stored in the 
image memory 52, image signals expected to be originally the same patterns 
such as image signals of each chip are compared with each other by the 
image comparator 53. Different portions are detected as defects. 
Information concerning defects including coordinates of positions where 
defects have occurred is stored in a memory of the image processor 25 or 
the whole controller 26 (step 35c). If all places to be inspected have 
been inspected, the object 20 to be inspected is unloaded from the wafer 
holder 21 (step 36c). 
Variants different from the above described correction processing of the 
inspection conditions in the inspection condition corrector 27a will now 
be described. 
In a first variant of the present embodiment, the CPU 131 calculates an 
average secondary electron yield ratio .eta. of a range registered and 
specified beforehand in the reference instead of calculating the secondary 
electron yield ratio .eta. of the place registered and specified 
beforehand in the reference. From the secondary electron yield ratio .eta. 
in an area of the upper layer pattern and an area of the lower layer 
pattern according to changes in the potential values E.sub.0, E.sub.2 and 
E.sub.2, the CPU 131 calculates an average secondary electron yield ratio 
.eta. of a range registered and specified beforehand in the external 
storage device (reference) 137 (a range including a plurality of 
repetitions of an area of the upper layer pattern and an area of the lower 
layer pattern). The CPU 131 selects such inspection conditions (potential 
values E.sub.0, E.sub.2 and E.sub.2) that this calculated average 
secondary electron yield ratio .eta. comes in a small value range around 
unity (i.e., it becomes a value which can be nearly approximated to 
unity). Thereby, the contrast .rho. falls to some degree. Since charge-up 
does not occur in an average manner on the surface of the object to be 
inspected, however, stable inspection can be conducted for a long time. 
In a second variant of the present embodiment, the CPU 131 calculates the 
average secondary electron yield ratio .eta. of the range registered and 
specified beforehand in the reference besides the calculation of the 
secondary electron yield ratio .eta. of a place registered and specified 
beforehand in the reference, and selects such inspection conditions that 
the weighted average of them is close to unity. In other words, the CPU 
131 calculates the secondary electron yield ratio .eta. obtained from an 
area of the upper layer pattern according to changes of the potential 
values E.sub.0, E.sub.2 and E.sub.2 and the secondary electron yield ratio 
.eta. over the above described range, and selects such inspection 
conditions (potential values E.sub.0, E.sub.1 and E.sub.2) that the 
weighted average of them is close to unity. Thereby, the charge-up of the 
upper layer pattern and the average charge-up can be optimized, and stable 
inspection can be conducted for a long time. 
In a third variant of the present embodiment, the CPU 131 calculates the 
secondary electron yield ratio .eta. of a place specified by an operator 
instead of calculating the secondary electron yield ratio .eta. of the 
place registered and specified beforehand in the reference. In other 
words, an area on the wafer subjected to exposure to an electron beam is 
then made a new surface area on which charge-up does not occur, in 
response to a command given from the CPU 131. For this purpose, the stage 
controller 50 is driven and controlled via the whole controller 26. While 
the stage 46 having the wafer holder 21 installed thereon is thus being 
scanned, the potential controller 23 is controlled via the whole 
controller 26 so as to change the potential values E.sub.0, E.sub.1 and 
E.sub.2 with a predetermined pitch. In response to a command given via the 
whole controller 26, focus offset determined by the condition is set in 
the focus controller 22. In response to a command given via the whole 
controller 26, the wafer 20 is exposed to an electron beam from the 
electron source 14 via the objective lens 18. According to the changes in 
the potential values E.sub.0, E.sub.1 and E.sub.2, secondary electrons 
generated from the surface area of the repeated upper layer pattern and 
lower layer pattern on the wafer 20 are collected by the E.times.B 17. An 
image is thus detected by the secondary electron detector 16 and converted 
to a digital image signal by the A/D converter 24. According to the 
changes in the potential values E.sub.0, E.sub.1 and E.sub.2 obtained by 
the A/D converter 24, the CPU 131 stores the digital image obtained from 
the surface area of the repeated upper layer pattern and lower layer 
pattern on the wafer 20 in the image memory 133. The digital image 
according to the changes in the stored potential values E.sub.0, E.sub.1 
and E.sub.2 is displayed on the screen of the display device 136. For the 
digital image according to the changes in the stored potential values 
E.sub.0, E.sub.1 and E.sub.2, a place (area) where the secondary electron 
yield ratio .eta. is to be calculated is specified by using the input 
device 135. Thereby, the secondary electron yield ratio .eta. and the 
contrast .rho. can be calculated in this specified place (area). As a 
result, registration into the reference is not needed. Even for a pattern 
which does not necessarily have repetitions, inspection conditions can be 
chosen. While specifying the potential values E.sub.0, E.sub.1 and E.sub.2 
by using the input device 135 and observing the digital image according to 
changes of the potential values E.sub.0, E.sub.2 and E.sub.2 displayed on 
the screen of the display device 136, such inspection conditions 
(potential values E.sub.0, E.sub.1 and E.sub.2) that charge-up is not seen 
in the upper layer pattern and proper contrast .rho. is obtained can be 
directly chosen and stored in the external storage device 137 so as to be 
associated with the kind of the object to be inspected (section structure 
of the surface) without calculating the secondary electron yield ratio 
.eta. and the contrast .rho.. In the case where the CPU 131 attempts to 
correct the inspection conditions (potential values E.sub.0, E.sub.1 and 
E.sub.2) by calculating the secondary electron yield ratio .eta. and the 
contrast .rho., correction of the inspection conditions can be confirmed 
by displaying the corrected digital image on the screen of the display 
device 136. 
In a fourth variant of the present embodiment, the CPU 131 calculates an 
average secondary electron yield ratio .eta. of the entire image or in a 
range specified by the operator instead of calculating the secondary 
electron yield ratio .eta. of the place registered and specified 
beforehand in the reference. As a result, registration into the reference 
is not needed. Even for a pattern which does not necessarily have 
repetitions, inspection conditions (potential values E.sub.0, E.sub.1 and 
E.sub.2) can be chosen, and charge-up does not occur in an average manner. 
Therefore, stable inspection can be conducted for a long time. 
In a fifth variant of the present embodiment, the CPU 131 does not 
calculate the secondary electron yield ratio .eta. of the place registered 
and specified beforehand in the reference. Instead, the CPU 131 detects a 
digital image using secondary electrons in a plurality of scan methods 
(such as a method of changing the scan direction as shown in FIGS. 6B and 
6C or a method of scanning the same place a plurality of times in 
succession), calculates the degree of coincidence between them (i.e., the 
degree of absence of difference between digital images), and selects 
inspection conditions (potential values E.sub.0, E.sub.1 and E.sub.2) 
having a high degree of coincidence. In the case where charge-up occurs on 
the surface of the object to be inspected, a change should occur in the 
charge-up phenomenon by conducting scanning with an electron beam a 
plurality of times during a comparatively short time even if there is a 
charge-up ease phenomenon. In the case where a change is not seen (i.e., 
the degree of coincidence is high) between detected digital images, 
therefore, it is indicated that charge-up does not occur on the surface of 
the object to be inspected. Furthermore, as for the contrast .rho., it can 
be calculated from the detected digital image. Owing to this, inspection 
conditions can be chosen without a registered reference or specification 
by the operator. On the basis of a difference (change) between detected 
digital images, the charge-up phenomenon on the surface of the object to 
be inspected, on the contrary, can be grasped. 
In a sixth variant of the present embodiment, the CPU 131 does not 
calculate the secondary electron yield ratio .eta. of the place registered 
and specified beforehand in the reference. Instead, a pattern which can be 
detected as the same digital image signal even if the scan direction is 
changed by 180 degrees on the object is registered beforehand in the 
reference. By specifying a position of the pattern, an electron beam 172 
used to irradiate the pattern 171 is aligned via the whole controller 26 
as shown in FIG. 17. Thereafter, the scan direction of the electron beam 
is changed with respect to the pattern 171 by 180 degrees. Reciprocating 
scanning is thus conducted with the electron beam 172 as represented by 
173 and 174. A digital image signal obtained from one of scan lines is 
inverted by 180 degrees so as to form a mirror image. This inverted 
digital image signal is compared with a digital image signal obtained from 
the other scan line, and the degree of their coincidence is calculated. 
Inspection conditions (potential values E.sub.0, E.sub.1 and E.sub.2) 
having a high degree of coincidence and proper contrast .rho. calculated 
on the basis of a detected digital image are chosen. 
FIG. 17 shows an example of a pattern which should provide the same pattern 
when inverted by 180 degrees so as to form a mirror image. 
With respect to this pattern, an image obtained by scanning in the 
direction 173 and an image obtained by scanning in the direction 174 are 
acquired. One of the two images is inverted so as to form a mirror image, 
and comparison is effected. Originally, this pattern is a pattern which 
should provide the same pattern when inverted by 180 degrees so as to form 
a mirror image. If the degree of pattern coincidence is high, therefore, 
it can be said that pattern detection is accomplished normally. Otherwise, 
it is meant that the pattern detection is not proper. 
In the case where charge-up has occurred in the pattern 171, a tail 175 
appears in the downstream of the scan line in the pattern 171 as the 
digital image in each of the reciprocating scan lines 173 and 174. By 
comparing a digital image signal obtained by inverting a digital image 
obtained from one of the scan lines by 180 degrees with a digital image 
signal obtained from the other of the scan lines, therefore, the tail 175 
appears on both sides of the pattern 171 as noncoincidence (difference) in 
the case where charge-up has occurred in the pattern 171. If charge-up 
does not occur in the pattern 171, then the tail 175 does not appear in 
the downstream of the scan line in the pattern 171 as the digital image in 
each of the reciprocating scan lines 173 and 174, resulting in a high 
degree of coincidence. In other words, inspection conditions (potential 
values E.sub.0, E.sub.2 and E.sub.2) which do not cause the charge-up in 
the pattern 171 can be chosen. According to this variant, proper 
inspection conditions can be chosen without information of the section 
structure of the object to be inspected. By comparing a digital image 
signal obtained by inverting a digital image obtained from one of the scan 
lines by 180 degrees with a digital image signal obtained from the other 
of the scan lines and detecting the tail 175 appearing as noncoincidence 
(difference) on both sides of the pattern 171, the charge-up phenomenon 
which has appeared in the pattern 171 can be grasped. 
In a seventh variant of the present embodiment, the CPU 131 does not 
calculate the secondary electron yield ratio .eta. of the place registered 
and specified beforehand in the reference. Instead, a certain area on the 
object to be inspected is scanned with an electron beam a plurality of 
times to detect respective digital images as shown in FIGS. 9A and 9B. For 
example, a digital image detected in a first scan is compared with a 
digital image in a scan conducted a plurality of scans after, and the 
degree of coincidence between them is calculated. Inspection conditions 
(potential values E.sub.0, E.sub.2 and E.sub.2) having a high degree of 
coincidence and having proper contrast .rho. calculated on the basis of 
the detected digital image are chosen. If charge-up occurs in the upper 
layer pattern, a difference between a digital image detected in a first 
scan is compared with a digital image in a scan conducted a plurality of 
scans after, for example, becomes large. If on the contrary charge-up does 
not occur in the upper layer pattern, then the difference between a 
digital image detected in a first scan is compared with a digital image in 
a scan conducted a plurality of scans after, for example, is little and 
the degree of coincidence becomes high. Therefore, inspection conditions 
(potential values E.sub.0, E.sub.1 and E.sub.2) causing no charge-up in 
the upper layer pattern can be chosen. According to this variant, proper 
inspection conditions can be chosen without information of the surface 
section structure of the object to be inspected. In an eighth variant of 
the present embodiment, inspection conditions are not chosen 
automatically. Instead, the CPU 131 presents image quality evaluation 
parameters, such as the secondary electron yield ratio .eta. of a 
specified place, the degree of coincidence between digital images detected 
by using a plurality of scan methods, and contrast of digital images, to 
the operator by displaying them on the display device, for example. Thus, 
the operator selects inspection conditions. According to the present 
variant, proper inspection conditions can be chosen by using a simple 
configuration. 
In a ninth variant of the present embodiment, inspection conditions are not 
chosen automatically. Instead, the CPU 131 presents a digital image 
detected in association with changed potential values E.sub.0, E.sub.1 and 
E.sub.2 to the operator by displaying them on the display device 136, for 
example. Thus, the operator selects proper inspection conditions 
(potential values E.sub.0, E.sub.2 and E.sub.2) on the basis of the 
observed digital image. According to the present variant, proper 
inspection conditions can be chosen without information of the surface 
section structure of the object to be inspected and with a simple 
configuration. 
Furthermore, it is apparent that a plurality of variants heretofore 
described may be applied to select proper inspection conditions (potential 
values E.sub.0, E.sub.1 and E.sub.2). 
As heretofore described, the present embodiment makes it possible to 
inspect wafers (objects to be inspected) of various varieties and 
processes under proper inspection conditions (potential values E.sub.0, 
E.sub.2 and E.sub.2). In addition, it can be realized to inspect defects 
and dimensions of patterns on wafers (objects to be inspected) having 
various surface section structures not only of a specific variety but also 
of a plurality of processes. As a result, the present embodiment can be 
used as a fabrication pattern inspection system 216 as shown in FIG. 18. 
It can be realized to conduct on-line inspection on minute defects and 
dimensions in a resist pattern or an insulator pattern having a surface 
section structure which cannot be optically inspected in the middle of the 
flow of the fabrication process. As a matter of course, the inspection can 
be realized off-line. 
FIG. 18 shows the schematic configuration of a fabrication system using the 
embodiment of FIG. 16 as the fabrication pattern inspection system 216. In 
the fabrication system, wafers (semiconductor substrates) 212 are thrown 
into a fabrication line 211 and fabrication is conducted by using a large 
number of fabrication facilities 1 through n. Numeral 213 denotes a 
quality control network for controlling various fabrication conditions 
(including fabrication lots) inputted from terminals 2141 through 214n 
installed in association with a large number of fabrication facilities 1 
through n forming the fabrication line, and quality data inspected by a 
quality inspection system 215, a fabrication pattern inspection system 
216, and a probe tester 217. The quality control network 213 is connected 
to a quality control computer (not illustrated). Controllers installed in 
the fabrication facilities may be directly connected to the quality 
control network 213. 
The quality inspection system 215 is an inspection system for inspecting 
foreign particles and conducting line width measurements on the wafer 212 
fabricated as far as a desired fabrication system by taking at least a lot 
as the unit. As the quality inspection system 215, an inspection system 
for conducting optical inspection and an inspection system using an 
electron beam according to the present invention can be used. The quality 
inspection system 215 may conduct inspection on-line for the wafer 212 
fabricated as far as a desired fabrication system by taking at least a lot 
as the unit. By applying also an inspection system using an electron beam 
according to the present invention to measurement of dimensions of a 
resist pattern (having transparency with respect to light) subjected to 
exposure development, measurement and inspection results having higher 
precision as compared with the optical system can be obtained. 
By taking at least a lot as the unit for the wafer 212 fabricated as far as 
a desired fabrication system, the fabrication pattern inspection system 
216 inspects a circuit pattern formed on the surface of a wafer or an 
insulator pattern having through-holes formed therin. As the fabrication 
pattern inspection system 216, an inspection system for conducting optical 
inspection and an inspection system using an electron beam according to 
the present invention can be used. The fabrication pattern inspection 
system 216 may conduct inspection on-line for the wafer 212 fabricated as 
far as a desired fabrication system by taking at least a lot as the unit 
in the same way as the quality inspection system 215. By applying also an 
inspection system using an electron beam according to the present 
invention to defect inspection of an insulator pattern having 
through-holes formed therein, measurement and inspection results having 
higher precision as compared with the optical system can be obtained. 
The probe tester 217 is a device for inspecting all IC chips formed on a 
completed wafer for electric characteristics. From the probe tester 217, 
therefore, defect items are detected for each of chips on the wafer. 
The quality control computer analyzes inspection results obtained from the 
quality inspection system 215, the fabrication pattern inspection system 
216, and the probe tester 217 via the quality control network 213, thereby 
estimates the cause of the defect, and determines the fabrication process 
(fabrication system) giving rise to the defect cause. The information is 
reported to the terminal of the fabrication system. Manufacturing 
conditions are altered and amended so as to prevent the defect from 
occurring. 
A semiconductor is fabricated on a semiconductor substrate (wafer) via a 
film forming dry process for forming an insulator film such as an 
interlayer insulator film or a guard film and a wiring metal film, an 
etching dry process for forming an insulator film pattern having a circuit 
pattern and through-holes, an exposure development process for conducting 
resist coating and exposure development and forming a resist pattern, a 
resist removing process, a planarization process for planarizing the 
insulator film, and a cleaning process. Therefore, the semiconductor 
fabrication line is formed by disposing a large number of fabrication 
systems 1 through n having various processors for implementing the above 
described processes and controllers for controlling those processors. An 
electron beam inspection system according to the present invention is 
disposed between the above described desired fabrication systems. Patterns 
on wafers fabricated by a fabrication system are inspected by this 
inspection system. A result of pattern inspection is transmitted to the 
quality control computer via the quality control network 213. On the basis 
of this inspection data and past quality control data, the quality control 
computer inquires into the cause of the defect and reports it to the 
terminal of the fabrication facility giving rise to the cause of the 
defect. Upon receiving the report, the terminal conducts countermeasure 
control depending on the defect cause on the fabrication facility. In 
order to prevent occurrence of the defect, alteration and amendment 
(including cleaning) of the fabrication conditions (process processing 
conditions), i.e., control is effected. 
A third embodiment of a system for detecting a pattern on an object such as 
a semiconductor wafer by using an electron beam according to the present 
invention will now be described by referring to FIG. 19. The present 
system (apparatus) includes an electron source 14 for generating an 
electron beam, a beam deflector 15 for effecting a scan with the electron 
beam and conducting imaging, an objective lens 18 for focusing the 
electron beam on a wafer 20 which is the object to be inspected, a 
potential providing device 19 such as a grid disposed between the 
objective lens 18 and the wafer 20, a wafer holder 21 for holding the 
wafer 20 mounted thereon, a stage 46 for scanning and positioning the 
wafer holder 21, an E.times.B (a device provided with an electric field E 
and a magnetic field B) 17 for collecting secondary electrons generated 
from the surface of the wafer to a secondary electron detector 16, a 
height sensor 13, a focus controller 22 for adjusting the focus position 
of the objective lens 18 on the basis of the height information of the 
wafer surface obtained from the height sensor 13, a deflection controller 
47 for controlling the beam deflector 15 to conduct scanning with the 
electron beam, a potential controller 21 including a wafer holder 
potential adjuster 49 for adjusting the potential E.sub.0 of the wafer 
holder 21, a grid potential adjuster 48 for controlling the potential 
E.sub.1 of the voltage providing device 19 such as a grid, and an electron 
source potential adjuster 51 for controlling the voltage E.sub.2 of the 
electron source 14, an A/D converter 24 for conducting A/D conversion on a 
signal supplied from the secondary electron detector 16, an image 
processor 25 including an image memory 52 and an image comparator 53 to 
process the digital image subjected to A/D conversion in the A/D converter 
24, an inspection condition corrector 27b for correcting the inspection 
conditions on the basis of the surface section structure of the object 
obtained from the design information, an inspection condition setter 28 
for setting and storing inspection conditions corrected and chosen by the 
inspection condition corrector 27b, a stage controller 50 for controlling 
the stage 46, a whole controller 26 for controlling the whole of them, and 
an inspection vacuum chamber 45 for housing the electron source 14, the 
beam deflector 15, the objective lens (electric optics) 18, the voltage 
providing device 19 such as the grid, and the wafer 20 which is the object 
(sample). FIG. 19 differs from FIG. 16 in existence of the inspection 
condition corrector 27b. 
The sequence of the present system is shown in FIG. 14C. In this scheme, 
inspection conditions are preset on the basis of a plurality of materials 
forming the object 20 to be inspected. 
The correction of the inspection conditions conducted in the inspection 
condition corrector 27b will now be described. As shown in FIGS. 1 and 10, 
the CPU 131 theoretically calculates dependence of the secondary electron 
yield ratio .eta. upon the acceleration voltage E on the sample and the 
electric field .alpha. on the sample for a plurality of materials forming 
the surface section structure over the kinds of the object on the basis of 
experimental values inputted by using the input device 135, and stores the 
dependence in the external storage device 137. Subsequently, a plurality 
of materials (a material located in the upper layer and a material located 
in the lower layer) forming the surface section structure according to the 
kind of the object to be inspected are specified by using the input device 
135. The CPU 131 searches for inspection conditions (potential values 
E.sub.0, E.sub.1 and E.sub.2) having a value contained in a small 
permissible value range around unity (i.e., having a value equal to 
approximately unity) as the secondary electron yield ratio .eta. of the 
specified material located in the upper layer, having a value contained in 
a predetermined permissible value range such as the range of 0.7 to 1.2 as 
the secondary electron yield ratio .eta. of the material located in the 
lower layer, and having a proper value as the difference (contrast .rho.) 
from the secondary electron yield ratio .eta. of the material located in 
the upper layer. The CPU 131 stores such inspection conditions (potential 
values E.sub.0, E.sub.1 and E.sub.2) in the external storage device 137 as 
proper inspection conditions (step 37d). As a matter of course, a group of 
proper inspection conditions according to the kind are stored in the 
external storage device 137 over kinds of the object to be inspected. 
Actual inspection of wafers will now be described. Before actually 
inspecting a wafer, inspection conditions corresponding to the kind 
(including the variety and process) of a wafer to be inspected are chosen 
out of the group of the inspection conditions (potential values E.sub.0, 
E.sub.1 and E.sub.2) stored in the external storage device 137 and stored 
in the RAM 134. Subsequently, the wafer to be actually inspected is loaded 
in response to a command issued by the whole controller 26 (step 31d). 
Alignment is conducted (step 32d). Thereafter, the inspection conditions 
stored in the inspection condition setter 28 are read out. Each of the 
potential values E.sub.0, E.sub.1 and E.sub.2 is thus controlled by the 
wafer holder potential adjuster 49, the grid potential adjuster 48, and 
the electron source potential adjuster 51 forming the potential controller 
23. The focus offset determined by the conditions is set by the focus 
controller 22 (step 34d). After this setting, the stage 46 is driven in 
the Y direction at a predetermined speed under the control of the stage 
controller 50 in response to a command given from the whole controller 26. 
(As for this scan in the Y direction, scanning using the beam deflector 15 
may be used together therewith.) While the stage 46 is being thus driven 
in the Y direction, scanning is conducted in the X direction with the 
electron beam supplied from the electron source 14 by using the beam 
deflector 15 under the control of the deflection controller 47. 
Consecutive two-dimensional image signals are detected from the second 
electron detector 16, and converted to two-dimensional digital image 
signals by the A/D converter 24. The two-dimensional digital image signals 
are stored in the image memory 52 included in the image processor 25. 
Among detected two-dimensional digital image signals and two-dimensional 
digital image signals stored in the image memory 52, image signals 
expected to be originally the same (such as image signals of each of 
repeated chips, blocks, or unit areas (which may include a pattern)) are 
compared with each other by the image comparator 53. Different portions 
are judged to be defective on the basis of the inspection standard 
(judgment standard) and recorded in a memory included in the image 
processor 25 or the whole controller 26 (step 35d). If all places to be 
inspected on a wafer 20 have been inspected, the wafer is unloaded (step 
36d). 
In a first variant of the present embodiment, inspection conditions 
(potential values E.sub.0, E.sub.1 and E.sub.2) obtained as a result of 
search using only the information of the object to be inspected are not 
applied as they are. Instead, calibration is conducted by using the scheme 
described before with reference to the second embodiment (correction of 
inspection conditions based upon digital image signals obtained by 
detecting secondary electrons generated from the surface of the object to 
be inspected) in the neighborhood of inspection conditions (potential 
values E.sub.0, E.sub.1 and E.sub.2) obtained by searching. Thereby, 
inspection conditions suitable for the surface section structure of an 
actual wafer can be calculated. In other words, the charge-up phenomenon 
not only depends on the material of the pattern in the surface section 
structure but also changes according to the shape or thickness of the 
upper layer pattern. According to the present variant, accurate inspection 
conditions can be set in the shortest time. 
In the present embodiment as well, working effects similar to those of the 
above described embodiment can be obtained. In other words, wafers of 
various varieties and processes can be inspected under optimum inspection 
conditions. The present embodiment can be applied not only to a specific 
variety but also to wafers obtained in a plurality of processes. 
A fourth embodiment of the system for detecting (observing) a pattern on 
the object such as a semiconductor wafer by using an electron beam 
according to the present invention will now be described by referring to 
FIG. 20. FIG. 20 is a schematic configuration diagram showing an 
embodiment of an observation SEM according to the present invention. The 
present system (apparatus) includes an electron source 14 for generating 
an electron beam, a beam deflector 15 for effecting a scan with the 
electron beam and conducting imaging, an objective lens 18 for focusing 
the electron beam on an object 20, a potential providing device 19 such as 
a grid disposed between the objective lens 18 and the object, a wafer 
holder 21 for holding the object 20 mounted thereon, a stage 46 for 
scanning and positioning the object 20, an E.times.B (a device provided 
with an electric field E and a magnetic field B) 17 for collecting 
secondary electrons generated from the surface of the object to a 
secondary electron detector 16, a height sensor 13, a focus controller 22 
for adjusting the focus position of the objective lens 18 on the basis of 
the height information of the object surface obtained from the height 
sensor 13, a deflection controller 47 for controlling the beam deflector 
15 to conduct scanning with the electron beam, a potential controller 21 
including a wafer holder potential adjuster 49 for adjusting the potential 
E.sub.0 of the wafer holder 21, a grid potential adjuster 48 for 
controlling the potential E.sub.1 of the voltage providing device 19 such 
as a grid, and an electron source potential adjuster 51 for controlling 
the voltage E.sub.2 of the electron source 14, an A/D converter 24 for 
conducting A/D conversion on a signal supplied from the secondary electron 
detector 16, an image display unit 54 for displaying digital images 
obtained by A/D conversion conducted in the A/D converter 24 on a monitor 
55 such as a display, an inspection condition corrector 27b for correcting 
the inspection conditions on the basis of the surface section structure of 
the object obtained from the design information, an inspection condition 
setter 28 for setting and storing inspection conditions corrected and 
chosen by the inspection condition corrector 27b, a stage controller 50 
for controlling the stage 46, a whole controller 26 for controlling the 
whole of them, and an inspection vacuum chamber 45 for housing the 
electron source 14, the beam deflector 15, the objective lens (electric 
optics) 18, the voltage providing device 19 such as the grid, and the 
wafer 20 which is the object (sample). FIG. 20 differs from FIGS. 16 and 
18 in that the image display unit 54 and the monitor 55 are provided 
instead of the image processor 25. Since the inspection condition 
corrector 27b also has the monitor (display device) 136 in addition to the 
function of the image display unit 54, the monitor (display device) 136 
can be used instead of the monitor 55. 
As shown in FIG. 14C, the sequence of the present system is similar to that 
of the third embodiment. However, the inspection at the step 35d is 
conducted as hereafter described. In accordance with an order given by the 
operator, the stage 46 is driven in the Y direction at a predetermined 
speed under the control of the stage controller 50 in response to a 
command given from the whole controller 26. (As for this scan in the Y 
direction, scanning using the beam deflector 15 may be used together 
therewith.) While the stage 46 is being thus driven in the Y direction, 
scanning is conducted in the X direction with the electron beam supplied 
from the electron source 14 by using the beam deflector 15 under the 
control of the deflection controller 47. Consecutive two-dimensional image 
signals are detected from the second electron detector 16, and converted 
to two-dimensional digital image signals by the A/D converter 24. The 
two-dimensional digital image signals are stored in the image memory 52 
installed in the image display unit 54. The image display unit 54 cuts out 
a specified image out of image signals stored in the image memory, and 
enlarges and displays the image on the monitor 55 to present the image to 
the operator. Therefore, the operator can observe a specific partial image 
on the surface of the object with enlargement. According to the present 
embodiment, the surface of the object can be observed under such a 
condition that charge-up is not caused at any time, irrespective of a 
change of the material of the surface of the object. 
A fifth embodiment of the system for detecting a pattern on the object such 
as a semiconductor wafer by using an electron beam according to the 
present invention will now be described by referring to FIG. 21. FIG. 21 
is a schematic configuration diagram showing an embodiment of an pattern 
length measuring apparatus for inspecting dimensions of a pattern 
according to the present invention. The present system (apparatus) 
includes an electron source 14 for generating an electron beam, a beam 
deflector 15 for effecting a scan with the electron beam and conducting 
imaging, an objective lens 18 for focusing the electron beam on an object 
20, a potential providing device 19 such as a grid disposed between the 
objective lens and the object, a wafer holder 21 for holding the object 
20, a stage 46 carrying the wafer holder 21 to scan and position the 
object 20, an E.times.B (a device provided with an electric field E and a 
magnetic field B) 17 for collecting secondary electrons generated from the 
surface of the object to a secondary electron detector 16, a height sensor 
13, a focus controller 22 for adjusting the focus position of the 
objective lens 18 on the basis of the height information of the object 
surface obtained from the height sensor 13, a deflection controller 47 for 
controlling the beam deflector 15 to conduct scanning with the electron 
beam, a potential controller 21 including a wafer holder potential 
adjuster 49 for adjusting the potential E.sub.0 of the wafer holder 21, a 
grid potential adjuster 48 for controlling the potential E.sub.1 of the 
voltage providing device 19 such as a grid, and an electron source 
potential adjuster 51 for controlling the voltage E.sub.2 of the electron 
source 14, an A/D converter 24 for conducting A/D conversion on a signal 
supplied from the secondary electron detector 16, an image processor 25 
including an image memory for storing a digital image obtained by the A/D 
conversion in the A/D converter 24 and an measurement processor 56 for 
measuring dimensions of a predetermined pattern on the basis of the 
digital image stored in the image memory, an inspection condition 
corrector 27a for correcting the inspection conditions so as to correspond 
to the surface section structure of the object on the basis of the digital 
image obtained from the A/D converter 24, an inspection condition setter 
28 for setting and storing inspection conditions corrected and chosen by 
the inspection condition corrector 27a, a stage controller 50 for 
controlling the stage 46, a whole controller 26 for controlling the whole 
of them, and an inspection vacuum chamber 45 for housing the electron 
source 14, the beam deflector 15, the objective lens (electric optics) 18, 
the voltage providing device 19 such as the grid, and the wafer 20 which 
is the object (sample). FIG. 21 differs from FIGS. 16 and 19 in that 
dimensions of the pattern on the object to be inspected are measured in 
the image processor 25. For measuring the dimensions of the pattern in the 
image processor 25, there are needed data of the deflection value (scan 
value) of the electron beam supplied from the deflection controller 47 to 
the beam deflector 15 and the displacement value (travel value) 
representing the value of the travel of the stage effected by the stage 
controller 50. Therefore, data (position information) 221 of the 
deflection value (scan value) of the electron beam supplied from the 
deflection controller 47 to the beam deflector 15 and the displacement 
value (travel value) representing the value of the travel of the stage 
effected by the stage controller 50 are inputted to the image processor 
25. 
As shown in FIG. 14B, the sequence of the present system is similar to that 
of the second embodiment. At the step 35c, however, the stage 46 is driven 
in the Y direction at a predetermined speed under the control of the stage 
controller 50 in response to a command given from the whole controller 26. 
While the stage 46 is being thus driven in the Y direction, scanning is 
repetitively conducted at high speed in the X direction with the electron 
beam supplied from the electron source 14 by using the beam deflector 15 
under the control of the deflection controller 47. Consecutive 
two-dimensional image signals are detected from the secondary electron 
detector 16, and converted to two-dimensional digital image signals by the 
A/D converter 24. The two-dimensional digital image signals are stored in 
the image memory installed in the image processor 25. By using the data 
(position information) 221 of the deflection value (scan value) of the 
electron beam supplied from the deflection controller 47 to the beam 
deflector 15 and the displacement value (travel value) representing the 
value of the travel of the stage effected by the stage controller 50, 
dimensions of a desired pattern formed on the surface of the object are 
measured on the basis of the image data stored in the above described 
image memory. The results are stored in the memory included in the image 
processor 25 or the whole controller 26 and outputted and presented to the 
operator as occasion demands. 
According to the present embodiment, patterns on wafers of various 
varieties and processes can be measured under proper inspection 
conditions. Dimensions of patterns on not only a wafer of a specific 
variety but also wafers obtained in a plurality of processes can be 
measured accurately. As a result, the present embodiment can be used as 
the quality inspection system shown in FIG. 18. In the midcourse of a 
fabrication process, fine widths of resist patterns and insulator patterns 
which cannot be optically measured can be accurately measured. As a 
result, quality inspection can be implemented. 
Sixth through tenth embodiments of the system for detecting a pattern on 
the object such as a semiconductor wafer by using an electron beam 
according to the present invention will now be described by referring to 
FIGS. 22 through 27. FIG. 22 is a diagram showing a characteristic portion 
of the sixth embodiment of the system for detecting a pattern on the 
object such as a semiconductor wafer by using an electron beam according 
to the present invention. It is now assumed that in the sixth embodiment 
charge-up has occurred on the surface of the object 20 to be inspected. 
For the charge-up phenomenon appearing in the digital image signal 
obtained by converting an image signal using secondary electrons, for 
example, representing the physical property of the object detected by the 
sensor 11 (16) as shown in FIGS. 4 through 6, FIG. 8, and FIG. 17, the 
inspection standard (judgment standard) is changed in the image processor 
25. In this way, the influence of this charge-up is mitigated, and 
inspection can be conducted accurately. 
Operation conducted in the inspection condition corrector 27a in the 
embodiment shown in FIG. 22 will now be described. On the basis of the 
digital image signal representing the physical property of the object and 
using secondary electrons, for example, detected by the sensor 11 (16) 
according to the high-speed scan direction with the electron beam and 
converted by the A/D converter 24, the CPU 131 extracts a change area of 
the digital image signal due to charge-up (a change area due to charge-up) 
as shown in FIGS. 6B or 6C and FIG. 8B, for example, so as to correspond 
to the high-speed scan direction with the electron beam, for each of kinds 
differing in surface section structure of object. As occasion demands, the 
CPU 131 conducts charge-up judgment by deriving average brightness in the 
above described change area. For each kind of the object to be inspected, 
the result is stored in the external storage device 137. The extraction of 
the change area of the digital image signal due to occurrence of charge-up 
can be implemented by, for example, using two threshold values eliminating 
the brightness of the upper layer pattern area and eliminating the 
brightness of the lower layer pattern area. Because the brightness of the 
change area due to the charge-up lies between the brightness of the upper 
layer pattern area and the brightness of the lower layer pattern area. In 
the inspection condition corrector 27a, therefore, two-dimensional mask 
data (mask signal) indicating the change area due to charge-up for each of 
repeated chips, blocks or unit areas (as shown in FIGS. 6D, 6E and 8C, for 
example) are formed in the external storage device 137 for each of kinds 
of the object so as to be associated with the scan direction of high-speed 
scan using the electron beam. However, it is desirable to conduct 
processing for expanding only the change area on the two-dimensional mask 
data (mask signal) representing the change area generated by charge-up and 
store it in the external storage device 137 as mask data (mask signal) 
222. Furthermore, in repeated chips, blocks or unit areas on the objects 
of the same kind, there are in some cases surface section structures of a 
plurality of kinds having different charge-up phenomena. Therefore, it is 
necessary to prepare two-dimensional mask data so as to accommodate them. 
Alternatively, the inspection standard (judgment standard) in the change 
area due to charge-up may be determined on the basis of the average 
brightness in the above described change area derived by the CPU 131. 
Furthermore, the inspection standard (judgment standard) in areas other 
than the above described change area may be determined on the basis of the 
image contrast .rho. between the upper layer pattern area and the lower 
layer pattern area. 
Actual inspection of the object to be inspected (wafer) will now be 
described. First of all, the inspection condition setter 28 reads out a 
mask signal corresponding to the kind of the object specified at the time 
of actual inspection from the external storage device 137, and sets and 
stores the mask signal in the RAM 134. Subsequently, the stage 46 is 
driven in the Y direction at a predetermined speed under the control of 
the stage controller 50 in response to a command given from the whole 
controller 26. While the stage 46 is being thus driven in the Y direction, 
scanning is conducted in the X direction with the electron beam supplied 
from the electron source 14 by using the beam deflector 15 under the 
control of the deflection controller 47. Consecutive two-dimensional image 
signals are detected from the sensor 11 (the second electron detector 16), 
and converted to two-dimensional digital image signals by the A/D 
converter 24. The two-dimensional digital image signals are stored in the 
image memory 52 included in the image processor 25. Among detected 
two-dimensional digital image signals and two-dimensional digital image 
signals stored in the image memory 52, image signals expected to be 
originally the same (such as image signals of each of repeated chips, 
blocks, or unit areas) are compared with each other by the image 
comparator 53. At this time, mask data 222 stored in the RAM 134 are read 
out. On the basis of data (position information) 221 of deflection value 
(scan value) of the electron beam supplied from the deflection controller 
47 to the beam deflector 15 and displacement value (travel value) 
representing the value of travel of the stage effected by the stage 
controller 50, the mask data 222 read out is aligned with the 
two-dimensional digital image signal to be compared. On the basis of the 
mask data 222, the inspection standard (judgment standard) is made 
different in the change area from other areas. A portion where the image 
signals differ from each other is judged to be defective and is recorded 
in the memory in the image processor 25 or the whole controller 26. In 
other words, when image signals expected to be originally the same (such 
as image signals of each of repeated chips, blocks, or unit areas) are 
compared with each other by the image comparator 53, the inspection 
standard (judgment standard) is made different in the change area from 
other areas (for example, the sensitivity is lowered in the change area 
due to charge-up) on the basis of the mask data 222. As a result, false 
detection can be prevented even if a change is caused in the detected 
digital image signal by charge-up. 
As shown in FIG. 6, the change area due to charge-up changes mainly in 
relation to the high-speed scan direction with the electron beam. 
Therefore, the object 20 to be inspected is rotated by 90 or 180 degrees 
by rotating the wafer holder 21 by 90 or 180 degrees, for example. The 
scan direction with the electron beam is thus changed. Consecutive 
two-dimensional image signals are thus detected again from the sensor 11 
(secondary electron detector 16), converted to two-dimensional digital 
image signals by the A/D converter 24, and inspected in the image 
processor 25. By doing so, all areas can be inspected with the same 
inspection standard (judgment standard). 
FIG. 23 is a diagram showing a seventh embodiment of a system for detecting 
a pattern on the object such as a semiconductor wafer by using an electron 
beam according to the present invention. In the seventh embodiment shown 
in FIG. 24, the object 20 (28) is loaded. In response to a command issued 
by the whole controller 26, the stage 46 is aligned under the control of 
the stage controller 50. Thereafter, a certain chip, block, or unit area 
(which may include a pattern) is scanned once with the electron beam. 
Consecutive first two-dimensional image signals are detected from the 
sensor 11 (secondary electron detector 16), converted to first 
two-dimensional digital image signals by the A/D converter 24, and stored 
in an image memory 232 included in the inspection condition corrector 27c 
and the image memory 52 included in the image processor 25. Subsequently, 
the same chip, block, or unit area (which may include a pattern) is 
scanned with the electron beam a plurality of times. (The high-speed scan 
direction may be changed.) Consecutive second two-dimensional image 
signals are detected from the sensor 11 (secondary electron detector 16), 
and converted to second two-dimensional digital image signals by the A/D 
converter 24. In a charge-up decision unit 233 formed by a CPU and 
included in the inspection condition corrector 27c, difference values 
between the first two-dimensional digital image signals stored in the 
image memory 232 (133) and the second two-dimensional digital image 
signals are calculated. Two-dimensional mask data (mask signal) 
representing the change area due to charge-up (as shown in FIGS. 6D, 6E 
and 8C, for example) are formed and stored in a memory 234. However, it is 
desirable to conduct processing of expanding only the change area on the 
two-dimensional mask data (mask signal) representing the change area due 
to charge-up and store the result in the memory 234 as mask data (mask 
signal) 235. The inspection standard (judgment standard) in the change 
area due to charge-up may be determined on the basis of average brightness 
in the change area derived by the charge-up decision unit 233. 
Furthermore, the inspection standard (judgment standard) in areas other 
than the above described change area may be determined on the basis of the 
image contrast .rho. between the upper layer pattern area and the lower 
layer pattern area. Until the mask data 235 are thus created in the 
inspection condition corrector 27c, inspection is not executed in the 
image comparator 53. 
Actual inspection of the object to be inspected (wafer) becomes similar to 
that of the embodiment shown in FIG. 22. In response to a command issued 
by the whole controller 26, the stage 46 is driven in the Y direction at a 
predetermined speed under the control of the stage controller 50. While 
the stage 46 is being thus driven in the Y direction, scanning is 
conducted in the X direction with the electron beam supplied from the 
electron source 14 by using the beam deflector 15 under the control of the 
deflection controller 47. Consecutive two-dimensional image signals having 
repetitions of a chip, block, or a unit area are detected from the sensor 
11 (the second electron detector 16), and converted to two-dimensional 
digital image signals by the A/D converter 24. Among detected 
two-dimensional digital image signals and the first two-dimensional 
digital image signals stored in the image memory 52, image signals 
expected to be originally the same (such as image signals of each of 
repeated chips, blocks, or unit areas) are compared with each other. At 
this time, mask data 235 stored in the memory 234 are read out. On the 
basis of data (position information) 221 of deflection value (scan value) 
of the electron beam supplied from the deflection controller 47 to the 
beam deflector 15 and displacement value (travel value) representing the 
value of the travel of the stage effected by the stage controller 50, the 
mask data 235 read out is aligned with the first two-dimensional digital 
image signal to be compared. On the basis of the mask data 235, the 
inspection standard (judgment standard) is made different in the change 
area from other areas. A portion where the image signals differ from each 
other is judged to be defective and is recorded in the memory in the image 
processor 25 or the whole controller 26. In other words, when image 
signals expected to be originally the same (such as image signals of each 
of repeated chips, blocks, or unit areas) are compared with each other, 
the inspection standard (judgment standard) is made different in the 
change area from other areas (for example, the sensitivity is lowered in 
the change area due to charge-up) on the basis of the mask data 235. As a 
result, false detection can be prevented even if a change is caused in the 
detected digital image signal by charge-up. 
As shown in FIG. 6 and FIG. 17, the change area due to charge-up changes 
mainly in relation to the high-speed scan direction with the electron 
beam. Therefore, the object 20 to be inspected is rotated by 90 or 180 
degrees by rotating the wafer holder 21 by 90 or 180 degrees, for example. 
The scan direction with the electron beam is thus changed. Consecutive 
two-dimensional image signals are thus detected again from the sensor 11 
(secondary electron detector 16), converted to two-dimensional digital 
image signals by the A/D converter 24, and inspected in the image 
processor 25. By doing so, all areas can be inspected with the same 
inspection standard (judgment standard). 
FIG. 24 is a diagram showing an eighth embodiment of a system for detecting 
a pattern on the object such as a semiconductor wafer by using an electron 
beam according to the present invention. In the eighth embodiment of FIG. 
24, the same line is scanned on the surface of the object with an electron 
beam. While a reciprocating scan is being conducted or a scan is being 
conducted twice to effect a two-dimensional scan, consecutive 
two-dimensional image signals having repeated chips, blocks or unit areas 
are detected from the sensor 11 (secondary electron detector 16) and 
converted to two-dimensional digital image signals by the A/D converter 
24. Numeral 241 denotes a memory for storing a digital image signal of one 
preceding scan line obtained from the A/D converter 24 as a result of the 
reciprocating scan or scanning twice. The memory 241 is formed by a shift 
register. Numeral 242 denotes an image addition circuit for adding 
together the digital image signal of one preceding scan line obtained from 
the memory 241 and the digital image signal of one succeeding scan line 
obtained from the A/D converter 24. In the case of reciprocating scan, it 
is necessary in the image addition circuit 242 to read out the digital 
image signal of one preceding scan line from the memory 241 with inversion 
of 180 degrees. Numeral 243 denotes a gate circuit, which is closed during 
the preceding scan included in the reciprocating scan or two scans. 
In the embodiment shown in FIG. 24, the object 20 (28) to be inspected is 
loaded. In response to a command issued by the whole controller 26, the 
stage 46 is aligned under the control of the stage controller 50. 
Thereafter, a certain chip, block, or unit area (which may include a 
pattern) is scanned with the electron beam in a two-dimensional way by 
effecting a reciprocating scan or effecting two scans. Consecutive 
two-dimensional image signals for the reciprocating scan or two scans are 
detected from the sensor 11 (secondary electron detector 16), and 
converted to two-dimensional digital image signals for the reciprocating 
scan or two scans by the A/D converter 24. For the chip, block, or unit 
area, a difference between the two-dimensional digital image signal based 
upon a preceding scan line in the reciprocating scan or two scans obtained 
from the memory 241 and the two-dimensional digital image signal based 
upon a succeeding scan line in the reciprocating scan or two scans 
obtained from the A/D converter 24 is calculated in a charge-up decision 
unit 233 formed by a CPU and other components and included in an 
inspection condition corrector 27d. Two-dimensional mask data (mask 
signals) representing the change area due to charge-up (as shown in FIGS. 
6D, 6E and 8C) are thus formed and stored in a memory 234. However, it is 
desirable to conduct processing of expanding only the change area on the 
two-dimensional mask data (mask signals) representing the change area due 
to charge-up and store the result in the memory 234 as mask data (mask 
signal) 235. 
Actual inspection of the object (wafer) to be inspected is conducted in the 
same way as the embodiments shown in FIGS. 22 and 23. Since the 
two-dimensional digital image signal to be inspected is obtained by 
addition conducted in the addition circuit 242, the signal-to-noise ratio 
is improved and inspection with high reliability can be implemented. As 
the scan using the electron beam becomes complicated, however, it becomes 
necessary to align the digital image signal obtained by the reciprocal 
scan or two scans more accurately. 
FIG. 25 is a diagram showing a ninth embodiment of a system for detecting a 
pattern on the object such as a semiconductor wafer by using an electron 
beam according to the present invention. In the ninth embodiment shown in 
FIG. 26, image signals expected to be originally the same (such as image 
signals of each of repeated chips, blocks, or unit areas) are compared 
with each other and defect candidates are detected as noncoincidence in an 
image comparator 254. Two compared images including defect candidates are 
cut out respectively by cutout circuits 255 and 256 and stored temporarily 
respectively in image memories 257 and 258. In a detail analyzer 259, the 
inspection standard (judgment standard) is altered by using the 
two-dimensional mask data (mask signal) representing the change area due 
to charge-up. In this way, attention is paid to charge-up and it is made 
possible to inspect real minute defects. 
A delay circuit 251 functions to delay the digital image signals by a value 
corresponding to repeated chips, blocks or unit areas. The delay circuit 
251 is formed by a shift register, for example. Each of the image memories 
252 and 253 functions to store digital images of an area formed by a 
plurality of scan lines. An image comparator 254 functions to compare the 
image signals respectively stored in the image memories 252 and 253 and 
expected to be originally the same and extract defect candidates as 
noncoincidence. The cutout circuits 255 and 256 function to cut out 
digital image signals including defect candidates extracted by the image 
comparator 254 from the image memories 252 and 253 and store them in the 
image memories 257 and 258, respectively. The detail analyzer 259 conducts 
detailed analysis of digital images including defect candidates cut out 
respectively in the image memories 257 and 258 by altering the inspection 
standard (judgment standard) on the basis of the two-dimensional mask data 
(mask signal) representing the change area due to charge-up obtained from 
the inspection condition setter 28. Thus the detail analyzer can inspect 
real minute defects. In the case where it takes a long time for detail 
analysis, it is possible in the present embodiment to inspect real minute 
defects without synchronism with the occurrence of images detected from 
the sensor 11 (secondary electron detector 16) and without being 
significantly affected by charge-up. Especially for detecting real minute 
defects, it is necessary to align digital images with each other more 
accurately than the minute defect size to be detected. For that purpose, 
position deviation detection also becomes necessary. Furthermore, it is 
necessary to extract a plurality of features by using a plurality of 
parameters and effect judgment on the basis of inspection standard 
(judgment standard) prepared so as to conform to the extracted feature. 
Thus, it takes a long time to conduct detail analysis. 
FIG. 26 is a diagram showing a tenth embodiment of a system for detecting a 
pattern on the object such as a semiconductor wafer by using an electron 
beam according to the present invention. It is now assumed that a shrunk 
pattern is detected in the detected image due to charge-up as shown in 
FIG. 5B. In the case where image signals for each of repeated chips, 
blocks, or unit areas are compared with each other, patterns are shrunk in 
the same way in the compared image signals and consequently defects can be 
detected as noncoincidence. In the case where the structural features of 
pattern dimensions (such as a pattern width or thickness) are extracted, 
however, it is necessary to alter parameters for extracting structural 
features according to a change incurred in the detected image by 
charge-up. 
The tenth embodiment in this case will now be described by referring to 
FIG. 26. A reference target (reference sample) having the same surface 
section structure (especially the same material) as the object to be 
inspected and having dimensions measured by using another method and 
already known is placed on the wafer holder 21. The reference target is 
scanned with an electron beam in a two-dimensional way. Two-dimensional 
image signals are detected from the sensor 11 (secondary electron detector 
16) and converted to two-dimensional digital image signals by the A/D 
converter 24. In the inspection condition corrector 27a, a feature value 
such as a dimension of the reference target is calculated on the basis of 
the converted two-dimensional digital image signals, and a difference 
between it and a feature value such as a dimension of the reference target 
already known is derived. As shown in FIG. 5B, for example, a change rate 
of the feature value such as the shrinkage ratio of the pattern due to 
charge-up is calculated and stored in the external storage device 137. In 
the case where there are a large number of surface section structures, it 
is possible to reduce the number of prepared reference targets by grouping 
and conduct interpolation or compensation in each group by using design 
information of the surface section structure of the object to be 
inspected. 
In the inspection condition setter 28, a change rate 264 of the feature 
value according to the surface section structure of the object to be 
inspected is read out and set. As for parameter setter 261 included in the 
image processor 25, various parameters for structural feature extraction 
such as pattern dimensions (such as the pattern width and pattern 
thickness) according to the kind of the surface section structure of the 
object to be inspected are inputted thereto and stored therein. By 
specifying the kind of the object to be inspected, a parameter suitable 
for the desired kind of the object to be inspected is read out of various 
parameters for structural feature extraction such as pattern dimensions 
set and stored in the parameter setter 261. A compensator 262 executes 
compensation on the parameter thus read out according to the change rate 
264 of the feature value. 
In an image detected under a specific condition, the feature value to be 
measured changes. This change rate is read into the parameter setter 261. 
The change rate is applied in the compensator 262 to the measured feature 
value. The measured feature value is thus compensated to become a real 
value. 
On the basis of the compensated parameter, a structural feature value 
extractor 263 extracts the feature value (such as pattern dimensions) of 
the surface section structure from the two-dimensional digital image 
signal of the object 20 (28) obtained from the A/D converter 24. In other 
words, the structural feature value extractor 263 extracts the feature 
value of the surface section structure of the object on the basis of the 
data (position information) 221 of deflection value (scan value) of the 
electron beam supplied from the deflection controller 47 to the beam 
deflector 15 and displacement value (travel value) representing the value 
of the travel of the stage effected by the stage controller 50. In the 
structural feature value extractor 263, the parameter for extracting the 
structural feature value is thus compensated. As a result, the structural 
feature value on the surface of the object to be inspected can be 
extracted with due regard to the charge-up phenomenon occurring on the 
surface of the object 20 (28) to be inspected. 
By comparing the structural feature value (such as pattern dimensions) 
extracted in the structural feature value extractor 263 with the 
inspection standard (judgment standard), inspection can be executed. 
An eleventh embodiment of a system for detecting a pattern on an object 
such as a semiconductor wafer by using an electron beam according to the 
present invention will now be described by referring to FIG. 27. Numeral 
14 denotes an electron source, and numeral 15 denotes a beam deflector. 
Numeral 16 denotes a secondary electron detector. Numeral 21' denotes a 
wafer chuck for supporting an object 20 to be inspected such as a wafer 
with needles connected to the ground. Therefore, electric charges of the 
electrified object 20 to be inspected are released through the needles 
272. The charge-up ease phenomenon thus occurs. Numeral 46 denotes an X-Y 
stage. Numeral 271 denotes a line width measuring device for position 
monitoring which detects the position of the X-Y stage 46 and position 
coordinates on the object 20 to be inspected. Numeral 273 denotes an 
electron shower generator. The electron shower generator 273 blows an 
electron shower against the object 20 to such a degree that secondary 
electrons are not generated. The electron shower generator 273 thus 
counteracts positive charge-up and prevents occurrence of charge-up. 
Numeral 274 denotes an ion shower generator. The ion shower generator 274 
blows an ion shower against the object 20 to such a degree that secondary 
electrons are not generated. The ion shower generator 274 thus counteracts 
negative charge-up and prevents occurrence of charge-up. Numeral 275 
denotes a mesh electrode provided with negative potential. When a desired 
place of the object 20 to be inspected is exposed to the focused electron 
beam 5, the mesh electrode 275 functions to cause the secondary electron 
detector 16 to detect properly secondary electrons generated from the 
surface of the object 20 to be inspected. Numeral 24' denotes an image 
input unit for inputting two-dimensional secondary electron image signals 
detected by the secondary electron detector 16. The image input unit 24' 
includes an A/D converter 24. Numeral 25 denotes an image processor 
including the image memory 52 and the image comparator 53. On the basis of 
the two-dimensional secondary electron image signals inputted to the image 
input device 24' and the position coordinates on the object 20 obtained 
from the length measuring device 271 for position monitoring, the image 
processor 25 inspects the upper layer pattern and the like. Numeral 26 
denotes a control computer (whole controller). The control computer 26 
controls voltages supplied to the beam deflector 15, the X-Y stage 46, the 
electron shower generator 273, the ion shower generator 274, and the mesh 
electrode 275. Especially, the control computer (whole controller) 26 must 
effect control so as to prevent electrons and ions blown by the electron 
shower generator 273 and the ion shower generator 274 from affecting the 
secondary electron signals detected by the secondary electron detector 16. 
The eleventh embodiment may also be applied to the above described first to 
tenth embodiments. In the first to tenth embodiments, charges stored on 
the surface of the object 20 are counteracted by the electrons and ions 
blown by the electron shower generator 273 and the ion shower generator 
274. In the detected images based upon secondary electrons or 
back-scattered electrons, therefore, contrast, for example, can be kept in 
a nearly constant state temporally. 
The embodiments heretofore described bring about such an effect that it is 
possible to mitigate the charge-up phenomenon and charge-up ease 
phenomenon caused when an object is exposed to an electron beam, set 
inspection conditions suitable for the surface section structure of the 
object, and execute reliable inspection, measurement and image display of 
the object. 
The embodiments heretofore described bring about such an effect that it is 
possible to set inspection conditions suitable for the charge-up 
phenomenon and charge-up ease phenomenon caused when an object is exposed 
to an electron beam, and execute reliable inspection, measurement and 
image display of the object. 
The embodiments heretofore described bring about such an effect that 
semiconductor substrates in the middle of fabrication can be actually 
inspected in the semiconductor fabrication line and consequently highly 
reliable semiconductors can be obtained stably by using results of the 
inspection as control data for fabrication facilities forming the 
semicondutor fabrication line.