Substrate inspecting apparatus, substrate inspecting system having the same apparatus and substrate inspecting method

A substrate inspecting system 60 observes and inspect a semiconductor wafer pattern by irradiating the surface of the semiconductor wafer 11 with electron beams 31, and making a projection unit project in enlargement secondary electrons, reflected electrons and backward scattered electrons generated therefrom in the form of secondary electron beams 32 on an undersurface of an electron beam detecting unit 61, and form an image thereon. The substrate inspecting system 60 includes a parallel-plate type energy filter 33 in a projection system. The present invention discloses a substrate inspecting apparatus capable of detecting a voltage contrast defect on a sample with a high accuracy by separating the secondary electron beams and fetching a secondary electron beam having an energy over a predetermined value, and of quantitatively measuring this defect, a substrate inspecting system having this apparatus, and a substrate inspecting method.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a substrate inspecting apparatus 
using electron beams, a substrate inspecting system and a substrate 
inspecting method, and more particularly to an inspecting apparatus, an 
inspecting system and an inspecting method which are suitable for 
inspecting defects on a semiconductor wafer and a photo mask. 
With a higher integration of the semiconductor device, there has 
increasingly been enhanced a sensitivity required for detecting a defect 
and a foreign material on a semiconductor wafer and a photo mask. In 
general, a detection sensitivity under of a width of a pattern wire is 
needed for detecting the pattern defect and the foreign material which 
might cause a serious deterioration in terms of a quality of the product. 
Therefore, in the semiconductor wafer defect inspection with a design rule 
of 1/4 .mu.m or under, its pursue has come in recent years substantially 
to a limit of the pattern defect inspection based on an optical system. 
Such being the case, pattern defect inspecting apparatuses using electron 
beams have been developed as a substitute for the optical system 
inspection, which were disclosed in Japanese Patent Application Laid-Open 
Publication Nos.5-258703(1993) and 7-249393(1995). 
Japanese Patent Application Laid-Open Publication No. 7-249393 discloses a 
method and an apparatus for detecting a pattern defect on a semiconductor 
wafer which involve the use of the electron beams. FIG. 1 shows the 
pattern defect detecting apparatus. 
As illustrated in FIG. 1, a pattern defect detecting apparatus 80 comprises 
a primary optical system 81 including an electron gun, having a 
rectangular electron emission surface cathode, for irradiating a surface 
85 of a sample 82 with electron beams 88 each taking a rectangular shape 
in section, and a quadrupole lens system. The apparatus 80 also comprise a 
secondary electron detecting system 84 including an electron beam 
detecting unit 86 for detecting secondary electrons, reflected electrons 
and backward scattered electrons 83 generated on the sample, and a mapping 
projection optical element for forming on the detecting unit 86 
secondary/primary images of the secondary electrons, reflected electrons 
and backward scattered electrons 83, and further a detection signal 
processing circuit 87 for processing detection signals. 
In the pattern defect detecting apparatus 80, the section of the electron 
beam falling upon the sample surface takes not circular and square shapes 
but the rectangular shape, thereby reducing a scan time. Besides, an 
aspect ratio of the rectangular electron beam is properly set, thereby 
controlling a density of the electric current of the electron beams. 
Further, the image signals detected by the electron beam detecting unit 86 
are processed in parallel, and therefore this apparatus has such an 
advantage that the defect on the wafer pattern can be detected at a high 
speed. 
In the defect inspection using the electron beams, in addition to the 
detection of a minute pattern defect on the wafer surface, it is feasible 
to detect even a defect on the semiconductor wafer, which is derived from 
an electric continuity defect (such as open- and short-circuit) by 
utilizing an image contrast (voltage contrast) occurred due to a 
difference in electric potential on the sample surface. The defect with an 
abnormality of the electric conduction inducing the above voltage 
contrast, is known as a voltage contrast defect. The principle for 
detecting this voltage contrast defect will be explained with reference to 
the drawings. 
The sample surface is charged up upon the irradiation of the electron 
beams. A (positive/negative) polarity of the charging up at that time is 
determined based on a material of the surface of the semiconductor wafer 
as well as on an energy of the irradiated electrons. FIG. 2 is a sectional 
view schematically showing one example of the semiconductor wafer 
irradiated with the electron beams. When a semiconductor wafer 100 shown 
in FIG. 2 is irradiated with, e.g., electron beams 101 having a 
predetermined energy quantity, an electrically floating Al electrode 
pattern 92 on the wafer surface is charged up to the negative polarity. 
While on the other hand, when irradiated with the electron beams of which 
an acceleration voltage is on the order of 1 keV, a pattern 91 of an 
insulating layer composed of SiO.sub.2 etc. is charged up to the positive 
polarity. Further, if grounded as in the electrode pattern 93 even in the 
case of a pattern composed of the same material Aluminum (Al), the 
electron beams flow across the substrate, resulting in no charging up. 
Thus, the sample surface is charged up to the positive or negative 
polarity with a variety of values upon the irradiation of the electron 
beams, whereby the electric potential is induced on the sample surface. 
With this surface potential, there change an emission efficiency of the 
secondary electrons, the reflected electrons and the backward scattered 
electrons occurred on the sample, and a detection efficiency at which 
those electrons generated thereon are taken in by the detector. In the 
example shown in FIG. 2, there are a high emission efficiency and a high 
detection efficiency of the secondary electrons, reflected electrons and 
backward scattered electrons 102 occurred on the Al electrode pattern 92, 
and therefore a quantity of the detection signals by the electron detector 
is large. An electron emission efficiency of secondary electrons, 
reflected electrons and backward scattered electrons 103 occurred on the 
Al electrode pattern 93 becomes smaller due to the charging up than on the 
pattern 92. Hence, the quantity of the detection signals by the electron 
detector is smaller than in the case of the pattern 92. By contrast, on 
the insulating layer pattern 91, there are a large quantity of the 
secondary electrons, the reflected electrons and the backward scattered 
electrons which are absorbed to the substrate surface charged up to the 
positive polarity, and therefor the quantity of the detection signals is 
by far smaller than on other portions (the Al electrode patterns 92, 93). 
Such a change in the detection signal quantity which is based on the change 
in the surface potential of the sample, appears as an image contrast of 
the electron image formed by the projection unit. This electron image 
contrast is termed a voltage contrast. Generally, the voltage contrast 
appears in the form of the charging up of the secondary electron image on 
a scanning electron microscope, or is utilized for an EB tester analysis. 
The images of the secondary, reflected and backward scattered electrons, 
which are obtained by irradiating the surface of the semiconductor wafer 
with the electron beams, in variably contain the voltage contrast in 
addition to a contrast (configurational contrast) appearing depending on a 
configuration. Accordingly, if the electrical conduction defective 
portions such as the open- and short-circuits exist mutually in the 
interconnections and contact holes of the semiconductor interconnection 
pattern, the surface potentials at the defecting portions are different 
from the surface potential at the electrically normal portion, and 
consequently the voltage contrasts different from that at the normal 
portion appear. 
For example, as in a semiconductor wafer 110 shown in FIG. 3, 
interconnection patterns 112, 113 composed of tungsten (W) will be 
explained. The interconnection patterns 112, 113 are each so designed as 
to be grounded and must have a decreased detection rate of the secondary 
electrons, the reflected electrons and the backward scattered electrons. 
As shown in FIG. 3, however, the contact hole is not sufficiently formed 
in the interconnection pattern 113, resulting in a state of the 
open-circuit. A large amount of the secondary electrons, the reflected 
electrons and the backward scattered electrons are thereby detected from 
the interconnection pattern 113, and it follows that the voltage contrast 
different from the electrically normal portion is detected in the 
detection image. The voltage contrast, of which an electric conduction 
condition is different from the normal portion, is hereinafter referred to 
as an abnormal voltage contrast. 
Thus, the electric conduction defective portion on the semiconductor wafer 
can be inspected by detecting the abnormal voltage contrast. 
There arises, however, a problem inherent in the prior art described above, 
wherein a detection accuracy of the abnormal voltage contrast declines for 
the following reason. 
Namely, the surface potential of the voltage contrast defect is estimated 
to be under 10V, and hence it is required that a voltage contrast image 
corresponding to a difference in terms of the surface potential be used 
for detecting the above-described defect. Accordingly, when forming an 
image of the electrons having an energy width over the surface potential 
difference, an energy component exceeding the surface potential difference 
turns out to be a noise component, which might be a factor for 
deteriorating the detection accuracy of the abnormal voltage contrast. 
According to the prior art described above, the images of the electrons in 
all the energy ranges of the secondary electrons, the reflected electrons 
and the backward scattered electrons generated on the wafer serving as a 
sample, are formed on the detector, and hence it follows that the voltage 
contrast images obtained therefrom are formed of the electrons exhibiting 
the continuous energies. Therefore, the problem is that it is therefore 
difficult to detect a minute different in the surface potential on the 
wafer sample. 
Further, in the prior art discussed above, it is unfeasible to 
quantitatively measure an electric characteristic of the voltage contrast 
defect from the obtained voltage contrast image. 
As explained above, the defect electric characteristic such as the contact 
resistance value reflects in the surface potential of the wafer sample. 
Accordingly, if capable of quantitatively measuring the surface potential 
with respect to the voltage contrast image, the electric characteristic 
can be quantitatively measured, and its effect is extremely large. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a substrate 
inspecting apparatus, a substrate inspecting system including this 
apparatus and a substrate inspecting method which are capable of detecting 
a voltage contrast defect on a sample with a high accuracy, and 
quantitatively measuring this defect. 
The substrate inspecting apparatus according to the present invention 
comprises an electron beam energy filtering element for separating 
secondary electron beams according to every energy component corresponding 
to an electric state on the surface of a sample, and fetching the 
separated secondary electron beam, whereby an S/N ratio of an image signal 
representing a physical/electric state on the substrate surface can be 
enhanced. This enables especially a detection sensitivity to be enhanced 
in the voltage contrast defect inspection for detecting from a difference 
in the surface potential a defect from which to cause an abnormality in 
electric conduction. 
When the electron beam energy filtering element is a magnetic field type 
energy filter for separating the electron beams according to each of a 
plurality of energy regions and fetching the separated electron beam, and 
if a plurality of electron beam detecting units are provided corresponding 
to the plurality of energy regions, signal images of the plurality of 
energy regions can be simultaneously taken in. 
The substrate inspecting method according to the present invention 
comprises a step of separating the secondary electron beams according to 
every energy region, and fetching the separated secondary electron beam, 
and it is therefore feasible to inspect a physical/electric state on the 
substrate surface with an excellent detection sensitivity. 
The substrate inspecting system according to the present invention, which 
includes the substrate inspecting apparatus, operates based on the 
substrate inspecting method described above and is therefore capable of 
inspecting the physical/electric state on the substrate surface with the 
excellent detection sensitivity. Particularly when controlling a voltage 
applied to the electron beam energy filtering element so that a quantity 
of detection signals becomes fixed, a relative surface potential can be 
measured from a quantity of change in a control voltage, so that an 
electric characteristic of the voltage contrast defect, such as a 
resistance value, etc. can be quantitatively measured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiment so the present invention will hereinafter be discussed 
with reference to the accompanying drawings. 
Note that the same components are marked with the same reference numerals 
throughout the following drawings, and repetitive explanations thereof are 
properly omitted. 
FIG. 4 is a block diagram showing a basic construction of a substrate 
inspecting system in a first embodiment of the present invention. A 
substrate inspecting system 60 in the first embodiment is characterized by 
including an electron beam energy filtering elements designated by the 
numerals 33, 34 in FIG. 4. 
To start with, the construction of the substrate inspecting system 60 in 
the first embodiment will be explained. 
The substrate inspecting system 60 shown in FIG. 4 includes a primary 
electron beam irradiating unit, a control unit thereof, a sample 11, a 
control unit of the sample 11, a secondary electron beam projection unit, 
a control unit thereof, an electron beam detecting unit 61, control units 
26, 67 thereof, an electron beam deflector 27 and a control unit 28 
thereof. The sample 11 is defined as a substrate such as a semiconductor 
water and a photo mask etc, and in the first embodiment the semiconductor 
wafer (hereinafter simply referred to as a water) is exemplified as a 
sample. 
As illustrated in FIG. 4, the electron beam irradiating unit is disposed 
with a skew to the direction perpendicular to the surface of the wafer 11, 
and an optical axis of the secondary electron beam projection unit in the 
direction perpendicular to the surface of the wafer 11. With this 
configuration, a primary electron beam 31 is incident upon the electron 
beam deflector 27 from a direction inclined to the surface of the wafer 
11, and the irradiating direction of the electron beam 31 is deflected by 
the electron beam deflector 27 in a direction perpendicular to the surface 
of the sample, thus impinging upon the wafer 11. Upon receiving the 
irradiation of the primary electron beam 31, secondary electrons, 
reflected electrons and backward scattered electrons are generated on the 
surface of the wafer 11, and, with a rotation-symmetry type electrostatic 
lens 14 producing an electric field in the vicinity of the surface of the 
wafer 11, led and accelerated in the direction perpendicular to the 
surface. Those electrons emerge from the surface of the sample 11 and are 
incident as secondary electron beams upon a projection optical unit. 
The electron beam irradiating unit has an electron gun and two-stage 
quadrupole lenses 5, 6. The electron gun includes a cathode 1 composed of 
lanthanum hexaboride (LaB.sub.6) which has an electron emission surface 
taking a rectangle having a dimension of 100 .mu.m.times.10 .mu.m, a 
wehnelt electrode (Wehnelt cylinder) formed with a rectangular opening, an 
anode 3 formed with a rectangle opening, and a beam-axis control deflector 
4. The control units 7, 8, 9 control an acceleration voltage of the 
irradiated electron beam, an emission current and the optical axis. The 
electron beam irradiating unit further includes two-stage electrostatic 
quadrupole lenses 5, 6 and control unit 10 thereof in order to form a 
rectangular beam on the order of 100 .mu.m.times.25 .mu.m on the surface 
of the wafer 11. Note that the electron beam irradiating unit may be 
constructed so that a sectional configuration perpendicular to the 
irradiating direction of the primary electron beam 31 is not limited to 
the rectangle but may be linear or an elongate ellipse on condition that 
an aspect ratio thereof is over 1. The acceleration voltage of the primary 
electron beam 31 is determined based on a relationship between a 
resolution of the projection unit and an incidence voltage upon the wafer 
11. 
The primary electron beams 31 are emitted from the cathode 1 and converged 
by the quadrupole lenses 5, 6. The primary electron beams 31 then emerge 
from the electron beam irradiating unit and strike on the electron beam 
deflector 27. The primary electron beams 31 deflected by the electron beam 
deflector 27 then emerge out of the electron beam deflector 27. 
Next, a flux of the primary electron beams 31 is reduced by the 
rotation-symmetry type electrostatic lens 14 and thereafter falls 
vertically upon the surface of the wafer 11. A voltage from a power source 
15 is applied to the rotation-symmetry type electrostatic lens 14. 
The sample unit is provided with a substrate stage 12 of which an upper 
surface is mounted with the wafer 11, a control unit 13 thereof and a 
power source 45, and is structured such that the voltage can be applied to 
the sample 11. The power source 45 applies a negative voltage to the wafer 
11. The substrate stage 12 is so structured as to be movable and moves 
under the control of the control unit 13, whereby the surface of the wafer 
11 can be scanned by the primary electron beams 31 through the movement of 
the stage. 
Herein, a value of the voltage applied to the wafer 11 is determined based 
on a performance of resolution of the projection unit. For obtaining a 
resolution of, e.g., 0.1 m or under, a high energy is required of the 
voltage of the secondary electron beam 32, and it is therefore preferable 
that the sample application voltage be 5 kV. On the other hand, an energy 
of the primary electron beam 31 is determined from a difference the sample 
application voltage and the incidence voltage upon the sample 11. What is 
generally used as an incidence voltage upon the wafer 11 is on the order 
of 800 V in terms of avoiding the wafer 11 from being damaged by the 
irradiation of the electron beams and preventing the wafer 11 from being 
charged up. As a result, the voltage of the primary electron beam 31 
becomes approximately 5.8 kV. 
When the sample 11 is irradiated with the primary electron beams 31, the 
secondary electrons, the reflected electrons and the backward scattered 
electrons, which retain pieces of data on a configuration, a material and 
an electric potential of the surface of the water 11, are emitted from the 
surface of the wafer 11. The rotation-symmetry type electrostatic lens 14 
generates the acceleration electric field between the electrostatic 
lenses, and, with this acceleration electric field, the electrons are led 
and thereafter accelerated in the direction perpendicular to the surface 
of the sample 11. The secondary electrons, the reflected electrons and the 
backward scattered electrons are thereby incident taking a form of 
secondary electron beams 32 upon the electron beam deflector 27 while 
making a trajectory parallel to the beam axis. Herein, the electron beam 
deflector 27 is controlled on such a condition as to permit the secondary 
electron beams 32 incident thereon from the side of the sample 11 to 
travel straight, and the secondary electron beams 32 therefore travel 
straight through within the electron beam deflector 27 and is thus 
incident upon an electron beam energy filtering element characteristic of 
the present invention. This electron beam energy filtering element 
transmits only the electron beams bearing an energy greater than a 
predetermined energy value with respect to the energy of the secondary 
electron beams 32 composed of the secondary electrons, the reflected 
electrons and the backward scattered electrons which have been generated 
on the wafer 11, and makes these transmitted electron beams incident upon 
the projection unit. A function of the electron beam energy filtering 
element will hereinafter be explained in greater details. 
The projection unit includes three stage rotation-symmetry type 
electrostatic lenses. The secondary electron beams 32 are projected in 
enlargement by the rotation-symmetry type electrostatic lenses 16, 18, 20 
to form an image on an MCP (Micro Channel Plate) detector 22. The control 
units 17, 19, 21 control voltages of the respective electrostatic lenses. 
An electron beam detecting unit 61 has the MCP detector 22, a fluorescent 
surface 23, a light guide 24, and a CCD camera 25 including a CCD area 
sensor. The secondary electron beams 32 incident upon the MCP detector 22 
are so amplified by the MCP detector 22 as to be raised to the fourth or 
fifth power of an electron quantity when incident, and thus fall upon the 
fluorescent surface 23. A fluorescent image, which is thereby formed on 
the fluorescent surface 23, is detected by the CCD area sensor through the 
light guide 24. Signals of the detected image are transmitted as image 
data via a control unit 67 to a host computer 28. The host computer 28 
makes the image data displayed on a display unit 29, and an image signal 
processing unit 30 executes predetermined image processing thereon, and 
the processed data are stored in a memory 58. In the first embodiment, the 
fluorescent image is taken in by the CCD area sensor but may also be taken 
in by a TDICCD (Time Delay Integration Charge Coupled Device) sensor in 
synchronization with a movement of the substrate stage 12. This method is 
highly effective in the inspection at a higher speed. 
Herein, a construction of the beam deflector 27 will be explained in brief 
with reference to FIGS. 5 and 6. 
FIG. 5 is a sectional view fully showing the construction of the beam 
deflector 27 provided in the substrate inspection system 60 illustrated in 
FIG. 4. 
As shown in FIG. 5, the beam deflector 27 has such a structure that an 
electric field E is orthogonal to a magnetic field B within the plane 
perpendicular to the beam axis of the projection unit (which is called an 
E.times.B structure). 
Herein, the electric fields E are generated by parallel-plate electrodes 
40a, 40b. The electric fields generated respectively by the parallel-plate 
electrodes 40a, 40b are controlled respectively by control units 43a, 43b. 
On the other hand, the magnetic fields B are generated by the 
electromagnetic coils 41a, 41b based on such a geometry that the 
electromagnetic coils 41a, 41b are disposed orthogonally to the 
parallel-plate electrodes 40a, 40b for generating the electric fields. A 
pole piece assuming a parallel-plate shape is provided for enhancing a 
uniformity of the magnetic field. 
FIG. 6 is a sectional view taken along the line A--A in FIG. 5. The 
irradiated primary electron beams 31 are, as shown in FIG. 6, deflected by 
the electric fields E generated by the parallel-plate electrodes 40a, 40b 
and by the magnetic fields B generated by the electromagnetic coils 41a, 
41b, and thereafter fall upon the rotation-symmetry type electrostatic 
lens 14 (see FIG. 4). The primary electron beams 31 penetrating the 
rotation-symmetry type electrostatic lens 14 are vertically incident on 
the surface of the sample 11 (see FIG. 4). On the other hand, the 
secondary electron beams 32 composed of the secondary electrons, the 
reflected electrons and the backward scattered electrons produced on the 
surface of the sample 11, are accelerated by the acceleration electric 
field generated between the sample 11 and the rotation-symmetry type 
electrostatic lens 14, and travel in the direction perpendicular to the 
surface of the sample 11. Then, the secondary electron beams 32, after 
having penetrated the rotation-symmetry type electrostatic lens 14, strike 
again on the beam deflector 27. 
Herein, a position and an angle of incidence of the primary electron beam 
31 upon the beam deflector 27, are univocally determined if the energies 
of the electron beams 31, 32 are determined. Further, for allowing the 
secondary electron beams 32 to travel straight, the respective control 
units 43a, 43b, 44a, 44b control the electric fields generated by the 
parallel-plate electrodes 40a, 40b and the magnetic fields generated by 
the electromagnetic coils 41a, 41b so as to satisfy a condition of the 
electric field E and the magnetic field B, i.e., vB=eE, where v is the 
velocity (m/s) of the secondary electron beams 32, B is the magnetic field 
(T), e is the electric charge quantity (C), and E is the electric field 
(V/m). The secondary electron beams 32 thereby travel straight through the 
electron beam deflector 27 and fall on the projection unit. 
Next, an image obtaining method involving the use of the electron beam 
energy filtering element characteristic of the first embodiment, will be 
described referring to FIG. 7. 
The electron beam energy filtering element includes a parallel-plate type 
energy filter 33 and a control unit 34 thereof. FIG. 7 is a schematic 
diagram showing the parallel-plate type energy filter 33 provided in the 
electron beam energy filtering element in the first embodiment. 
The parallel-plate type energy filter 33 shown in FIG. 7 includes mesh 
electrodes 35, 37 grounded, a mesh electrode 36 to which a voltage is 
applied, and the control unit 34 for applying the voltage to the mesh 
electrode 36. Herein, supposing that Vf be the voltage applied to the mesh 
electrode 36, only an electron beam 32a, having an energy equal to Vt or 
greater, among the secondary electron beams 32 penetrates the 
parallel-plate type energy filter 33. While on the other hand, an electron 
32b having an energy under Vf is forced back to the sample 11 by dint of a 
deceleration electric field generated between the electrode 37 and the 
electrode 36. 
The energy filter 33 having the configuration shown in FIG. 7 is capable of 
enhancing the filter voltage resolution most when the incident beam 32 is 
vertical to a filter electric field distribution. Accordingly, it is 
desirable that the parallel-plate type energy filter 33 be provided in an 
area in which the secondary electron beams 32 travel in parallel to the 
beam axis, i.e., provided between the electron beam deflector 27 and the 
rotation-symmetry type electrostatic lens 16, which meets a 
beam-collimated optical condition. Further, a projection unit provided 
other than between the electron beam deflector 27 and the 
rotation-symmetry type electrostatic lens 16, is formed with an optical 
system for collimating the secondary electron beams 32, and, if the 
electron beam energy filtering element is provided therein, the same 
effect can be expected. Note that even if provided in a non-collimated 
area, there is obtained the effect itself based on the energy separation, 
however, there must be a drawback in which the energy resolution might be 
deteriorated. 
FIG. 8 is a characteristic diagram showing a relationship between the 
applied voltage Vf to the electrode 36 with respect to a sample surface 
potential Vs and a signal intensity detected by the electron beam detector 
61. As shown in FIG. 8, when the electrode voltage Vf is increased toward 
a positive voltage with respect to the sample surface potential vs, the 
signal intensity decreases, thus depicting a characteristic curve 51 known 
as an S-curve. This S-curve characteristic is influenced by the surface 
potential of the sample 11, and, in a region of being charged up to a 
positive potential in the surface area of the sample 11, the energy of the 
secondary electron beams diminish, with the result that the S-curve shifts 
on the left side. By contrast, in a region of being charged up to a 
negative potential, the energy of the secondary electron beams augments, 
and hence the S-curve shifts on the right side. Let an S-curve 51 be a 
characteristic curve of the detection signal intensity in a certain region 
where the sample surface potential increases on the positive side, and an 
S-curve 52 be a characteristic curve of the detection signal intensity in 
another region where the sample surface potential increases on the 
negative side. It follows that a shift quantity 56 of the electrode 
voltage Vf between the S-curves 51, 52 corresponds to a surface potential 
difference of the sample 11. 
Referring to FIG. 8, the S-curves 51, 52 approach to each other in a 
voltage region 54 with a small value of Vf-Vs and a voltage region 55 with 
a large value of Vf-Vs in an area along the axis of abscissa indicating 
the electrode voltage Vf-the sample surface voltage vs. It can therefore 
be understood that a high S/N ratio is unable to be obtained from the 
signals of both of them. While on the other hand, a voltage region 57 
therebetween, there appears a large difference in terms of the signal 
intensity between two surface potential states, and hence it is feasible 
to obtain a preferable S/N ratio. Such a characteristic is applied to a 
relative surface potential measurement base on the EB testing. 
In the first embodiment, the wafer 11 is irradiated with the primary 
electron beams 31 each taking the rectangular shape, and the secondary 
electron beams 32 composed of the secondary electrons, the reflected 
electrons and the backward scattered electrons produced on the wafer 11 
are projected to form the image. Therefore, what is important for 
detecting a change in the surface potential at a voltage contrast 
detective spot from the images within the irradiated area, is the S/N 
ratios of the image signals of the defective spot and the non-defective 
portion (the good quality portion). Let an S-curve 51 be a signal 
intensity characteristic of the image signal based on the secondary 
electron beams emerging from the non-defective portion, e.g., a wiring 
pattern 112 of a wafer 110 shown in FIG. 11, and let an S-curve 52 be a 
signal intensity characteristic of the image signal based on the secondary 
electron beams emerging from the electrically defective spot, e.g., a 
wiring pattern 113 of a wafer 110 shown in FIG. 11, wherein it is feasible 
to largely enhance the S/N ratios of the image signals of the defective 
spot and the non-defective portion by setting the electrode voltage Vf 
under the condition as shown in a broken line 53. 
Further, from the image signals detected by the electron beam detecting 
unit 61, the filter voltage vf is controlled so that a quantity of the 
signals from the voltage contrast defecting spots becomes fixed, and a 
quantity of this fluctuation is monitored, thereby making is possible to 
quantitatively measure a relative surface potential at the voltage 
contrast defective spot. The electric characteristic such as a resistance 
value of the voltage contrast defect can be thereby quantitatively 
measured. 
Next, a second embodiment of the substrate inspection system according to 
the present invention is explained with reference to the drawings. 
FIG. 9 is a block diagram showing a basic construction of the substrate 
inspection system in the second embodiment. The components excluding the 
electron beam energy filtering element are the same as those in the first 
embodiment illustrated in FIG. 1. 
As obvious in the comparison with FIG. 1, the substrate inspection system 
in the second embodiment is characterized by the electron beam energy 
filtering element disposed in an optically conditional position where the 
secondary electron beams form a crossover, i.e., a position where the 
secondary electron beams converge at a minimum confusion circle of which 
the center exists at one point on the beam axis between a 
rotation-symmetry type electrostatic lens 20 and an electron beam 
detecting unit 61, and by a second electron beam detecting unit 62 for 
forming an image of a secondary electron beam 32b as a part of the 
secondary electron beams separated by the electron beam energy filtering 
element. 
In the second embodiment, the electron beam energy filtering element 
includes a magnetic field type energy filter 46 for generating a magnetic 
field orthogonal to the traveling direction of the secondary electron 
beams 32, and a control unit 63 thereof. The magnetic field type energy 
filter 46 permits a secondary electron beam 32a, having a high energy 
component, among the secondary electron beams 32 to travel straight, and 
the this secondary electron beam 32a is detected by an electron beam 
detecting unit 61. Further, the magnetic field type energy filter 46 
deflects at a large angle a secondary electron beam 32b having a low 
energy component. This deflected electron beam 32b is guided to an 
electron beam detecting unit 62, by which image data of the lower energy 
component thereof is detected. 
FIG. 10 is a perspective view showing a basic structure of the magnetic 
field type energy filter 46. As shown in FIG. 10, the magnetic field type 
energy filter 46 has electromagnet coils 38, 39 disposed in a face-to-face 
relationship with an optical path of the secondary electron beams 32 being 
interposed therebetween, and a current source 63 for exciting these 
electromagnet coils 38, 39. The electromagnet coils 38, 39 are excited by 
the current source 63, thereby inducing the magnetic field B in the 
direction orthogonal to the traveling direction of the secondary electron 
beams 32. 
FIG. 11 is a schematic view showing a trajectory of the electrons passing 
through the magnetic field type energy filter 46 shown in FIG. 7 as well 
as being a sectional view of FIG. 7 containing a virtual light source P, 
wherein the plane parallel to the side surfaces of the electromagnet coils 
38, 39 on the side of the electron beams, serves as a cutoff plane 
As shown in FIG. 11, the high-energy electrons 32a travel straight without 
being influenced by the deflection magnetic field, while the low-energy 
electrons 32b are deflected by the magnetic field B and emerge at a 
predetermined angle from the magnetic field type energy filter 46. 
According to the parallel-plate type energy filter 33 (see FIG. 6) in the 
first embodiment, there is obtained the image of the electron beams 
bearing the higher energy than the filter voltage Vf, and it is required 
that the filter voltage Vf be changed for varying the energy component 
thereof. According to the magnetic field type energy filter 46 in the 
second embodiment, however, it is feasible to obtain simultaneously the 
images of the plurality of energy components simply by setting the 
deflection magnetic field fixed. Categories of the energy components are 
determined by a numerical quantity of the detecting units provided in the 
substrate inspecting apparatus. 
The substrate inspecting apparatus in the second embodiment is, as shown in 
FIG. 6, capable of simultaneously taking in images of two energy regions 
because of its being provided with two electron beam detecting units 61, 
62. 
Given next is an explanation of how the substrate is inspected by use of 
the Substrate inspecting apparatus of the present invention. 
When the substrate is irradiated with the electron beams, a local 
difference occurs in terms of the electric potential on the substrate 
surface corresponding to a configuration and a material of the substrate 
and a structure of an electric circuit based on thereon. This point will 
be explained more specifically referring to the drawings. 
FIGS. 12 and 13 are sectional views schematically showing a defective 
portion and a normal portion on a substrate 200. AS shown in FIGS. 12 and 
13, a semiconductor circuit device provided with a multi-layered wiring 
extending over a silicon dioxide layers 201 and 202. In the normal portion 
shown in FIG. 12, a second via plug 209a on the surface of the 
semiconductor substrate 200 is electrically connected to an impurity 
diffused layer 204 on the surface of the substrate via a second metal 
interconnection 208, a first via plug 207, a first metal interconnection 
206 and an electrode contact 205. Note that FIG. 12 shows a structure in 
which the via plug involves the use of tungsten, and the surface under 
which the tungsten is embedded is flattened by chemical mechanical 
polishing. 
When a primary beam 211 falls upon the surface of the via plug 209a shown 
in FIG. 12, a positive electric charge is produced on the surface of the 
via plug 209a. The multi-layered interconnection extending over to the via 
plug 209a and the impurity diffused layer 204 is, however, electrically 
normally conductive, and therefore the surface extending from the 
substrate 200 to the via plug 209a is supplied with electrons 203, thus 
effecting neutralization. 
By contrast, in the defecting portion shown in FIG. 13, an open-circuit 
defective portion 212 exists between the second via plug 209b and the 
second metal interconnection 208, and hence second via plug 209b is not 
electrically conductive to the impurity diffused layer 204. 
Accordingly, when the surface of the second via plug 209b shown in FIG. 13 
is irradiated with primary beams 211, electrons 203 do not migrate from 
the substrate 200, resulting in a floating state. Then, the electric 
potential on the surface relatively changes to positive in terms of a 
balance with a release quantity of the secondary electrons (210b). In this 
case, positive electric charges occurred on the surface of the via plug 
209b are not neutralized with the electrons migrating from the substrate, 
and a quantity of charging up is larger than in the case of being normally 
conductive as shown in FIG. 11. 
Thus, there appears the difference in the electric potential between the 
surfaces of the via plugs 209a, 209b irradiated with the electron beams, 
depending on whether or not there is the electric conduction between the 
via plug 209 and the impurity diffused layer 204. 
Such a potential difference on the surface of the substrate appears as a 
difference in terms of the energy quantity when the secondary electrons 
generated on the substrate surface fall upon a secondary optical system. 
Hence, an image forming condition of the secondary optical system under 
which the secondary beams generated from a portion exhibiting a different 
surface potential and incident upon the secondary optical system are 
projected to form an image on the electron detector, might differ per 
region on the substrate surface. 
Accordingly, if a correlation between the secondary optical system image 
forming condition and the substrate surface potential is obvious 
beforehand, the secondary optical system is controlled so that the 
secondary beams are projected to properly form the image on the MCP 
detector, whereby the change in the substrate surface potential can be 
quantitatively measured. 
FIG. 14 is a view showing an optical path of the electron beams when 
forming images of the electrons from a normal pattern and from a defective 
pattern. 
A stage 343 is mounted with a wafer 342 including a normal pattern 371 and 
an open-circuit defective pattern 372 coming into an electrically floating 
state, and is biased to the negative potential by a power source 344. 
This apparatus has a cathode lens 321, an aperture angle stop 325, an 
E.times.B type beam separator 341, a transfer lens 322, two-stage project 
lenses 323, 324, a field stop 326, and an electron detector 330 
constructed of an MCP detector 331, a fluorescent screen 332, a light 
guide 333 and an imaging element 334. 
A secondary electron beam 373a emerging from a normal via portion 371 is 
projected to form an image on the electron detector 330 through lens 
systems 321-324. By contrast, a defective via portion 372, as explained 
referring to FIG. 13, has a large amount of charging up quantity (positive 
electric charges), and it is therefore conceived that the surface 
potential thereof is higher in the positive direction than in the normal 
via portion 371. Hence, a secondary electron beam 374a released from the 
via portion 372 bears an energy lower by a potential difference between 
the via portions 371 and 372 than the secondary electron beam 373a, and 
becomes a electron beam of which an image is formed in front of the 
electron detector 330. As a result, an image the normal via portion 
appears in the form of a bright spot, while an image of the defective via 
portion appears as a dark spot. 
FIGS. 15A-15C are explanatory views showing one example of a defect 
inspecting method. 
As shown in FIG. 15A, a die (a chip) formed on the wafer 342 is scanned in 
the lateral direction (the X-direction), and when reaching the side end 
thereof, an adjacent row thereof is scanned reversely in the X-direction 
after moving the wafer 342 in the vertical direction (the Y-direction). 
With repetitions of this operation, the entire surface of the wafer is 
thus inspected. Three pieces of adjacent dice A1,A2,A3 are herein 
exemplified, and images obtained therefrom are illustrated in FIG. 15B. 
Paying attention to the die B, the image obtained from the die B is an 
image G2 shown in FIG. 15B. The image G2 is compared with an image G1 of 
the adjacent die A, and via portions (white via portions) VP1, VP8 
exhibiting a different brightness are extracted. It is unknown only from 
the comparison between the two images G1 and G2 which side, G1 or G2, a 
defect exists, and therefore successively a comparison between G2 and G3 
is made. The via portions VP1, VP8 are the same with G, G3, and are 
therefore, it proves, different with respect to only the image G2, whereby 
the defect shown in FIG. 15C can be detected. Such a comparison process 
involving the use of the three dice is referred to as a die-to-die 
comparison process. 
FIG. 16 shows a construction of a computer system 339 serving as a 
processing apparatus for executing the die-to-die comparison process. 
The host computer 339 includes an inspecting condition input unit 387 for 
inputting an inspecting condition, a measurement command unit 364 for 
suppling the respective control units with control signals till the 
measurement is finished since a measuring condition has been inputted, and 
an image display processing unit 366 for displaying an image on a display 
unit on the basis of a result of processing. In addition, the host 
computer 339 includes an image comparison processing unit 384 for 
comparing the images of the adjacent dice with each other, and a defective 
portion specifying unit 385 for specifying the defective portion from the 
compared result. Further, a memory 361 is connected to the image 
comparison processing unit 384 and the defective portion specifying unit 
385, and the images stored therein are used when in the comparing process. 
Upon receiving a result of this comparison, the image signal processing 
unit 358 executes the signal processing. 
Next, a method of detecting a defect in a pattern configuration will be 
explained with reference to FIGS. 17-19. 
FIG. 17 shows how an image of a wiring pattern is formed. The secondary 
electron beams generated from metal wiring areas 378, 379 are projected to 
form images on the detector 330, resulting in a bright pattern. On the 
other hand, the secondary electron beam generated on an insulating layer 
390 between these wiring areas is unable to form an image on the detector 
330 under the same image forming condition because of an energy of the 
secondary electron beam due to the charging up on the surface thereof, and 
turns out to be dark. Thus, the metal wiring areas are brightened, while 
the insulating layer between the wiring areas is darkened, thereby 
obtaining an image of the pattern in which a line and a space are 
alternately repeated as shown in FIG. 19B. 
Herein, FIG. 18 illustrates a case where a short-circuit defect occurs 
between the interconnections due to an abnormality of the pattern. What is 
shown as a defect in FIG. 18 is a short-circuit defect LE1 between the 
adjacent interconnections 378 and 379, which is attributed to a metal 
embedded in a scratch formed when executing a flattening process based on 
CMP. 
This short-circuit defect LE1 assumes the same potential as the metal 
interconnection, and hence the image is formed the same with the metal 
wiring area, showing the same contrast. 
FIGS. 19A-19C are views corresponding to FIGS. 16A-16C, wherein images 
obtained from dice A1, A2, A3 are designated by G1b, G2b, G3b in such a 
case that the short-circuit defect LE1 exists in the die A2. As in the 
case of FIG. 16, FIG. 19C shows an image obtained by comparing the three 
dice with each other. 
FIG. 20 shows a construction of the host computer 349 serving as a 
processing apparatus for performing the pattern inspection described 
above. A difference of the construction shown in FIG. 20 from the 
construction in FIG. 16 is only one point that the image comparison 
processing unit 384 and the defective portion specifying unit 385 are 
replaced with a configuration judging unit 386. 
In this pattern inspection processing apparatus, the measurement command 
unit 364 irradiates arbitrary three unit regions A1, A2, A3 with the 
electron beams while moving the stage 343 as indicated by a broken arrow 
line in FIG. 18A under a predetermined image-forming condition, thereby 
obtaining image signals of electron imges G1b, G2b, G3b of the unit 
regions A1, A2, A3 as shown in FIG. 19B. The pattern inspection processing 
apparatus then stores the memory 361 with these image signals. The three 
unit regions are not limited to the regions adjacent to each other, and 
any regions are selectable. The configuration judging unit 386 takes the 
electron images G1b, G2b, G3b out of the memory 361, then cores the wiring 
areas corresponding thereto, and fetches the wring area different with 
respect to only the electron image G2b. For instance, in the example shown 
in FIG. 19C, the short-circuit defect LE1, which is formed between the 
interconnection 378 and the interconnection 379 and short-circuits these 
interconnections, is extracted as an interconnection configuration defect 
within the unit region A2, and may be stored in the memory 361. 
In the embodiment illustrated in FIGS. 12 through 20, the filter is 
disposed in front of the electron detector, whereby the brightness and the 
darkness of the light can be separated more distinctly. 
As discussed so far, the present invention, which has been carried out by 
way of the embodiments given above, is not limited to those Embodiments 
and may be modified in a variety of forms within the scope of the present 
invention without deviating from the gist thereof. In the second 
embodiment, the images of the two energy regions are taken in by the two 
electron beam detecting units. For example, three or more electron beam 
detecting units may be provided, which implies that the images of the 
three or more energy regions can be simultaneously taken in. Further, a 
single electron be detecting unit is used instead of a plurality of 
electron beam detecting units obtaining the images of a plurality of 
energy regions, and, if the detection region is divided within this single 
electron beam detecting unit and an image is obtained independently per 
divided detection region, the same effect can be acquired. 
Moreover, the components of the respective units may properly be changed 
corresponding to the specifications. In the embodiments discussed above, 
the uniform deflection magnetic field type separator has been exemplified 
as the magnetic field type energy filter, however, the same effect can be 
obtained even when using an electric field/magnetic field overlap type 
separator such as an electromagnetic field prism and a Wiener filter. 
Note that the inspecting system used for detecting the defect and the 
foreign material on the semiconductor wafer has been explained in the 
embodiments discussed above, however, as a matter of course, the present 
invention is applicable to the inspections of the substrates such as a 
photo mask etc without being confined to the semiconductor wafer.