Photomask inspection apparatus

A photomask inspection apparatus includes a photoelectric converting portion, a first comparator, buffer memories, a design data converting portion, and second and third comparators. The photoelectric converting portion converts the respective beams of light having separately scanned adjoining identical unit patterns formed on a photomask into electrical signals. The first comparator compares these electrical signals with each other to find whether there is any inconformity between the unit patterns, and when any inconformity is found, the first comparator outputs coordinate information of the inconformity. The buffer memories store the electrical signals respectively when the inconformity is found by the first comparator. The design data converting portion converts only design data of peripheral coordinates of the coordinate information in the design data stored in the external memory into an inspection signal. The second and third comparators compare the electrical signals from the buffer memories with the inspection signal to identify a photomask pattern having a defect.

BACKGROUND OF THE INVENTION 
The present invention relates to a photomask inspection apparatus and, more 
particularly, to a photomask inspection apparatus to be used upon 
manufacturing semiconductor integrated circuit. 
There are two inspection methods for inspecting a defect on a photomask. A 
first inspection method is a pattern comparison method in which adjacent 
unit patterns are compared with each other to inspect the difference 
therebetween. A second inspection method is a database verifying 
inspection method in which an actual pattern is compared with a design 
pattern to make an inspection. 
A photomask inspection apparatus capable of simultaneously executing the 
inspections according to the above-mentioned two methods is disclosed in 
Japanese Patent Laid-Open Publication No. Hei 2-108947. FIG. 2 is a 
structural view of the apparatus disclosed by the above reference. As 
shown in the figure, a central control unit 12 operates so that a flush 
switch 3 turns on light sources 4R and 4L, and then optical signals 
D.sub.R1 and D.sub.L1 from right and left unit patterns 2R and 2L on a 
mask 2, which has been obtained through lenses 5R and 5L, are converted 
into comparison signals D.sub.R2 and D.sub.L2 by a photoelectric 
converting portion 6. 
The comparison signal D.sub.R2 is subjected to intensity adjustment and 
division by an amplifier 13 and a division circuit 14 so as to be 
converted into signals D.sub.R3 and D.sub.R4 which are inputted into two 
comparators 9a and 9b respectively. The comparator 9a compares the 
comparison signal D.sub.L2 with the signal D.sub.R3 and stores defect 
information obtained by the pattern comparison method between the unit 
patterns 2L and 2R on the photomask 2 into a buffer memory 10a. 
On the other hand, the comparator 9b compares the comparison signal 
D.sub.R4 with a comparison signal D.sub.2 which is generated by a design 
data converting portion 8 from design data D.sub.1 recorded in an external 
memory 7, and stores defect information obtained by the database verifying 
inspection method into a buffer memory 10b. When an output instruction is 
inputted from a console 1, each defect information stored in the buffer 
memories 10a and 10b is outputted to an external output unit 11. 
However, in the above conventional photomask inspection apparatus, since 
the defect information shown in the external output unit 11 must be 
analyzed, there are some cases where it is difficult to determine which of 
adjoining chips contains defects such as an error in size of a contact 
hole. 
Further, in the conventional photomask inspection apparatus, since the 
design data converting portion 8 must convert all the design data in the 
external output unit 11, there is a problem that a long time is required 
to convert the design data. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a photomask inspection 
apparatus capable of determining which of adjoining chips contains a 
defect. 
Another object of the present invention is to provide a photomask 
inspection apparatus capable of shortening a data conversion time and 
executing inspection at high speed. 
A photomask inspection apparatus according to the present invention 
comprises a measuring system for converting the respective beams of light, 
which have separately scanned two adjoining identical unit patterns formed 
on a photomask, into a first electrical signal and a second electrical 
signal, comparing the first and second electrical signals with each other 
to detect whether or not the adjoining identical unit patterns are 
inconformity with each other, and when inconformity is found, outputting 
coordinate information of the inconformity; first and second memory 
circuits for storing the first and second electrical signals when the 
inconformity is found by the measuring system; a third memory circuit for 
storing design data of a pattern formed on the photomask; and identifying 
means for identifying a photomask pattern having a defect by comparing an 
inspection signal obtained from the design data stored in the third memory 
circuit with output signals from the first memory circuit and the second 
memory circuit respectively. 
With the above construction, when there is a difference between two 
adjoining identical unit patterns (adjoining chips) formed on the 
photomask, the output signals are compared with the design data so that it 
is possible to automatically determine which of the adjoining chips 
contains the defect. 
Further, since there is provided a design data converting portion for 
converting only design data of peripheral coordinates including the 
coordinate information from the measuring system in design data stored in 
the third memory circuit, if there is a difference between the adjoining 
chips, only the design data of the periphery of the coordinate information 
in the stored design data is converted into the inspection signal.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is shown a photomask inspection apparatus 
according to an embodiment of the present invention, in which the same 
components as those in FIG. 2 are designated by the same reference 
characters to unit the further description thereof. In FIG. 1, this 
photomask inspection apparatus include a console 1 for inputting pattern 
information of a photomask 2, right and left two optical sources 4L and 4R 
connected to a flush switch 3 and for scanning right and left identical 
unit patterns 2L and 2R on the photomask 2, right and left two lenses 5L 
and 5R for focusing beams of light having passed through the right and 
left unit patterns 2L and 2R, a photoelectric converting portion 6 for 
converting the focused scanning beams into electrical signals, a design 
data converting portion 8 for reading design data stored in an external 
memory 7 to convert the data into an electrical signal, a comparator 9a 
for comparing the electrical signals obtained from the right and left unit 
patterns, buffer memories 10a and 10b for temporarily storing information 
of the right and left unit patterns respectively when the comparator 9a 
detects a difference between the right and left unit patterns, a division 
circuit 14 for dividing the electrical signal from the design data 
converting portion 8 into two electrical signals, comparators 9b and 9c 
for comparing the information of the right and left unit patterns stored 
in the buffer memories 10a and 10b with the electrical signals from the 
division circuit 14, a buffer memory 10c for temporarily storing defect 
information obtained from the comparators 9b and 9c, and an external 
output unit 11 for retrieving the defect information in the buffer memory 
10c. 
In operation, design data D.sub.1 used for preparing the photomask 2 is 
inputted into the external memory 7, and the photomask 2 is attached to 
the apparatus. Next, pattern structure information is inputted from the 
console 1. This causes a central control unit 12 to operate so that the 
flush switch 3 turns on the light sources 4L and 4R. 
The scanning beams from the light sources 4L and 4R pass through the right 
and left unit patterns 2L and 2R of the photomask 2 to be made optical 
signals D.sub.L1 and D.sub.R2, and further are focused by the right and 
left two lenses 5L and 5R onto a light receiving surface of the 
photoelectric converting portion 6 to be converted into comparison signals 
D.sub.L2 and D.sub.R2. 
The comparator 9a compares the comparison signal D.sub.L2 related to the 
unit pattern 2L of the photomask 2 with the comparison signal D.sub.R2 
related to the unit pattern 2R of the photomask 2. When the comparator has 
found the difference therebetween, the comparator inputs coordinate 
information d as defect information obtained by the pattern comparison 
method into the design data converting portion 8, and at the same time, 
the comparator inputs the comparison signals D.sub.L2 and D.sub.R2 as 
comparison signals D.sub.L3 and D.sub.R3 having differences into 
corresponding buffers memories 10a and 10b, respectively, so that the 
signals are temporarily stored therein. 
On the other hand, the design data converting portion 8 generates an 
inspection signal D.sub.2 for the periphery of the defect portion from the 
design data D.sub.1 read from the external memory 7 on the basis of the 
coordinate information d inputted from the comparator 9a. The inspection 
signal D.sub.2 is supplied to the division circuit 14, and is divided into 
two signals D.sub.3 and D.sub.4 by the division circuit 14. 
The comparator 9b compares the comparison signal D.sub.L4 read from the 
buffer memory 10a with the inspection signal D.sub.3 taken from the 
division circuit 14. If the comparator finds a difference therebetween, 
defect information obtained by the database verifying inspection method is 
stored in the buffer memory 10c. Further, at the same time, the comparator 
9c compares the comparison signal D.sub.R4 read from the buffer memory 10b 
with the inspection signal D.sub.4 taken from the division circuit 14. If 
the comparator finds a difference therebetween, defect information 
obtained by the database verifying inspection method is stored in the 
buffer memory 10c. 
In this state, when an output instruction is inputted from the console 1, 
the defect information stored in the buffer memory 10c is outputted to the 
external output unit 11. As described above, in this embodiment, in the 
case where there is a difference between two adjoining unit patterns 2L 
and 2R (adjoining chips) formed on a photomask 2, the inspection signal 
D.sub.2 of the periphery of the defect information portion is generated 
from the design data D.sub.1 on the basis of the coordinate information d, 
and the inspection signal is compared with the two comparison signals 
related to the right and left unit patterns, so that it is possible to 
automatically determine which of the adjoining chips contains a defect. 
Further, in this embodiment, the design data converting portion 8 is 
operated such that only in the case where there is a difference between 
the two comparison signals related to the right and left identical unit 
patterns 2L and 2R, the coordinate information d is generated and only the 
design data of the periphery of the defect information portion in the 
design data D.sub.1 is converted to generate the inspection signal 
D.sub.2. Thus, the apparatus of the present invention is able to shorten a 
data conversion time as compared with a conventional apparatus in which 
all the design data in the external memory 7 is converted, and the 
photomask inspection result can be quickly obtained. 
As described above, according to the present invention, in the case where 
there is a difference between two adjoining identical unit patterns 
(adjoining chips) formed on a photomask, it is possible to automatically 
determine which of the adjoining chips contains a defect, so that it is 
possible to determined which of the chips contains a defect even if it is 
such a defect as an error in size of a contact hole, whereby more accurate 
photomask inspection can be executed as compared with the prior art. 
Further, according to the present invention, in the case where there is a 
difference between the adjoining chips, only design data of the periphery 
of the coordinate information in all the design data is converted into an 
inspection signal, so that the data conversion time can be shortened as 
compared with the conventional apparatus in which all the design data in 
the external memory is converted, and the photomask inspection result can 
be quickly obtained. 
It is apparent that the present invention is not limited to the above 
embodiment but may be changed and modified without departing from the 
scope and spirit of the invention.