Arrangement for inspecting circuit patterns drawn on a mask

A mask inspection arrangement is disclosed including a magnetic disc memory for storing pattern data which has been used for operating a mask drawing apparatus, a data producing device for optically scanning a mask drawn by the mask drawing apparatus and producing measured data indicative thereof, a data converter for converting the pattern data from memory into a reference data in the form of dot pattern data for blanking an electron beam in the mask drawing apparatus, and a comparator for comparing the measured data with the reference data and determining a correlation therebetween.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
The invention relates in general to integrated circuit manufacture. More 
specifically, the invention is directed to a method and an apparatus for 
inspecting a mask for an integrated circuit. 
2. Description of the Prior Art 
Mask drawing apparatus are used to draw circuit patterns for large scale 
integrated (LSI) circuits by using electron beams. Mask inspection 
apparatus are used to inspect whether the circuit patterns are correctly 
drawn by the mask drawing apparatus. 
Various arrangements for drawing the circuit patterns and inspecting them 
have been independently developed by different LSI manufacturers. Thus, a 
user of mask drawing apparatus and mask inspection apparatus may buy them 
from different manufacturers. 
As a result, there is often an incompatibility problem. The pattern data 
format used for operating the mask inspection apparatus may be different 
from the pattern data format being used for operating the mask drawing 
apparatus. To address this problem many users have a data conversion 
process or system through which the pattern data used for the mask 
inspection apparatus may be produced from either a CAD system (Computer 
Aided Design) which produces the pattern data for mask drawing, or from 
the pattern data used for the mask drawing apparatus. 
FIG. 1 (PRIOR ART) illustrates a known system including a mask drawing 
apparatus and a mask inspection apparatus. This system requires a data 
conversion process or system as discussed above. CAD system 1 produces a 
data group in a CAD format, which corresponds to a circuit pattern 8. 
Circuit pattern 8 is stored on a magnetic tape 9. 
A computer 2 converts the data group stored on magnetic tape 9 into pattern 
data having a format (A) used for a mask drawing apparatus 4. The pattern 
data is stored on a magnetic disc memory 3 having a large memory capacity. 
The data group having CAD format stored on magnetic tape 9 is converted by 
a data conversion system 7 to pattern data having a format (B) used for a 
inspection apparatus 6, which detects defects of circuit patterns drawn on 
a mask. The converted pattern data is stored on a magnetic disc memory 5. 
With increasing density of LSI circuits, masks for the LSI circuits and the 
reticles, on which an original circuit pattern figure is magnified, are 
being produced using electron beam drawing apparatus. When using an 
electron beam drawing apparatus, it is necessary to adopt a data format in 
which a larger data compression rate than that used in known processes is 
utilized. This requires a memory capacity sufficient to store a unit 
figure, such as for example a circle or a trapezoid. This capacity can be 
smaller as the degree of integration for an LSI circuit pattern increases. 
A data format known as "trapezoid format" has been used as a pattern data 
format for operating electron beam drawing apparatus. 
In using an electron beam drawing apparatus (hereinafter referred to as an 
"EB" apparatus) as a mask drawing apparatus, magnetic disc memory 3 stores 
pattern data having a trapezoid format (the trapezoid format is 
hereinafter, also called "EB format") as the format (A) data shown in FIG. 
1. 
In the case of converting pattern data having format (A) (here 
corresponding to EB format), a pattern data having format (B) is used. 
Data conversion system 7 includes hardware and software for data 
conversion interposed between disc memory 3 and disc memory 5. System 7 
needs additional time for operating format conversion of pattern data than 
would be required without such format conversion. 
Also, format conversion through data conversion system 7 may produce some 
errors in the process of converting because of added system complexity, as 
compared with a system wherein formats A and B are similar. 
Thus, in the case of the process of converting CAD format data stored on 
magnetic tape 9 to pattern data having format (B) through system 7, the 
conversion process itself requires too much time. 
SUMMARY OF THE INVENTION 
The present invention thus provides a method and apparatus for inspecting a 
drawn mask by utilizing pattern data used for drawing the mask to inspect 
the finished product. Pattern data used to draw the mask is stored in a 
memory such as, for example, a magnetic disc memory. This data is recalled 
and compared with data generated by optically scanning the finished 
product. 
The method and apparatus of the invention eliminate the data conversion 
system required in known systems which may produce errors during the 
process of data conversion. Eliminating the data conversion system saves 
time necessary for converting one format of a pattern data to another 
format. 
The method and apparatus of the invention reflect the inventor's 
recognition that there are some time-intervals between the time when 
drawing on a photo mask terminates and the time when inspecting the drawn 
mask begins. A mask on which drawing has just finished must be processed 
through some chemical treatment before it is inspected. 
The invention takes advantage of this interval of time. The present 
invention provides a novel mask inspection apparatus which comprises a 
memory for storing pattern data used for operating a mask drawing 
apparatus in which pattern data is converted from CAD format data, a 
measured data producing device for producing measured data by means of 
optically or electrically scanning a mask drawn by the drawing apparatus, 
a data conversion device for converting the pattern data to a reference 
data, and a comparing device for comparing the measured data with the 
reference data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 2, 3 and 4 illustrate various combinations of devices according to 
the present invention. They utilize a magnetic disc memory for storing 
pattern data for both inspection and mask drawing apparatus. 
In the FIG. 2 system, a computer aided design system 70 produces CAD format 
data which is stored on a magnetic tape 101. A mask drawing apparatus 102 
includes a computer 64 for converting CAD format data read from magnetic 
tape 101 into pattern data. This pattern data is, in turn, stored in a 
magnetic disc memory 103 by operating a format conversion program of 
computer 64. The pattern data stored in magnetic disc memory 103 is 
converted into dot pattern data by operating computer 64 and a converter 
59 in mask drawing apparatus 102, and a mask drawing operation is 
executed. 
A mask drawn by mask drawing apparatus 102 is subjected to some kind of 
chemical treatment. It is then mounted on a table of a mask inspection 
apparatus 104. During the chemical treatment a computer 25 reads out the 
pattern data from magnetic disc memory 103, which has already been used 
for the mask drawing operation of mask drawing apparatus 102. The read out 
pattern data is converted into "reference" data in a circuit 22 (similar 
to converter 59) of mask inspection apparatus. 
FIG. 3 illustrates another system arrangement according to the present 
invention. This system includes including two magnetic disc memories 105 
and 106, and two magnetic tapes 101 and 107 which store CAD format data 
produced in advance by a CAD system 70. Computer 64 converts CAD format 
data stored in a magnetic tape 101 into pattern data by operating its 
format conversion program, and stores it in magnetic disc memory 105. 
Then, mask drawing apparatus 102 operates to draw a circuit pattern on a 
mask by converting pattern data stored in magnetic disc memory 105 into 
dot pattern data. Computer 64 also transfers the pattern data previously 
stored an magnetic disc memory 105, to another magnetic disc memory 106. 
Time intervals necessary for transferring pattern data are very small 
compared with that of converting CAD format data stored on magnetic tape 
101 into pattern data stored in magnetic disc memory 105. The transferred 
pattern data stored in magnetic disc memory 106 is used for mask 
inspection in a mask inspection apparatus 104. 
Computer 64 may read out again, by operating its format conversion program, 
another CAD format data corresponding to another mask pattern from 
magnetic tape 101 and convert it into pattern data and store it in 
magnetic disc memory 105 while the mask inspection apparatus operates. 
Alternatively, computer 25 converts, by operating its format conversion 
program, CAD format data stored in a magnetic tape 107 into pattern data 
and stores it in magnetic disc memory 106. Then, computer 64 transfers the 
pattern data being stored in magnetic disc memory 106 to disc memory 105. 
In short, pattern data applied to mask inspection apparatus 104 for mask 
inspection is stored in magnetic disc memory 106 by transferring it from 
magnetic disc memory 105 or by converting CAD format data from magnetic 
tape 107. Priority for operating each operation program stored in computer 
64 or 25 is predetermined to avoid conflict in access to magnetic disc 
memories 105 and 106. Computer 64 is higher in priority than computer 25 
because it is impossible for computer 25 to access magnetic disc memory 
105. Computers 64 and 25 also operate to convert CAD format data stored in 
magnetic tape 101 and 107 into pattern data and to store them in magnetic 
disc memory 105 and 106 as a background job, as well as operate to draw 
circuit pattern figure on a mask and inspect it as a foreground job. 
FIG. 4 illustrates a more flexible system alternative as compared with the 
FIGS. 2 and 3 systems. Mask drawing apparatus 102 and mask inspection 
apparatus 104 may receive pattern data from either a magnetic disc memory 
108 or 109. To accomplish the flexibility of pattern data reception, 
priority concerning selections between magnetic disc memory 108 and 109 is 
predeterminedly defined in operation programs of computers 64 and 25. 
Therefore, CAD format data stored in magnetic tapes 101 and 107 may be 
stored in either of magnetic disc memory 108 or 109 by operating format 
conversion programs in either computer 64 or computer 25. 
In the case that pattern data (1) corresponding to CAD format data (1) is 
stored in magnetic disc memory 108, CAD format data (2) stored in magnetic 
tape 107 is converted into pattern data (2) by computer 25, which in turn 
is stored in magnetic disc memory 109. 
Pattern data (1) stored in magnetic disc memory 108 is transferred to mask 
drawing apparatus 102 for drawing circuit patterns on a mask, and after 
chemical treatments, the drawn mask is mounted on mask inspection 
apparatus 104. 
The pattern data stored in magnetic disc memory 108 is transferred to mask 
inspection apparatus 104 for inspecting the drawn mask under the control 
of computer 25. Pattern data stored in magnetic disc memory 109 is 
transferred to mask drawing apparatus 102 under the control of computer 64 
and is used for drawing next circuit patterns on a mask. After drawing on 
the mask information stored in magnetic disc memory 109 is transferred to 
mask inspection apparatus 104 for inspection of the mask under the control 
of computer 25. 
Computer 25 reads out CAD format data corresponding to still another 
pattern data from magnetic tape 101 and converts it into pattern data 
which in turn is stored in magnetic disc memory 108 while computer 25 
operates appropriately for inspecting the mask. 
By sequentially processing mask drawing and mask inspecting as mentioned 
above, the system constitution illustrated in FIG. 4 may accomplish to a 
significantly production efficiency than was possible with known systems. 
Mark Inspection Apparatus (MI) 
FIG. 5 is a block diagram of a mask inspection apparatus 104. A light 
source 11 connected with a power source 26 provides light, which is 
focused by a focusing lens 12, on a mask pattern 15 drawn on a mask 14 
fixedly mounted on a X-Y table 13 of mask inspection apparatus 104. Mask 
pattern 15 focuses into an image through an objective lens 16 onto a diode 
sensor 17. 
Diode sensor 17, excited by a sensor driving circuit 18, measures 
transmission light quantity at each point of a width on mask pattern 15 
equal to a sensitive area of diode sensor 17 in the direction of axis X. 
For measuring whole areas of mask pattern 15, X-Y table 13 is continuously 
moved in increments of a predetermined length in the direction of a Y axis 
perpendicular to X axis by means of a table driving circuit 20 controlled 
by computer 25. After scanning a first area having the width and the 
predetermined length on the mask pattern 15, X-Y table 13 is moved by the 
predetermined width to the direction of X axis for scanning a second area 
on mask pattern 15. Sensor driving circuit 18 converts a signal detected 
by diode sensor 17 to a digital signal, and transmits it to a judging 
circuit 23 and a deviation detecting circuit 24. 
A position detecting circuit 19 for detecting X and Y position of X-Y table 
13 comprises, for instance, a laser interferrometer. Position detecting 
circuit 19 operates in synchronism with sensor driving circuit 18 and also 
applies each detected position data, which corresponds to light 
transmission quantity data detected at each point of the sensitive area on 
diode sensor 17, to circuit 22 for producing reference data for judging 
circuit 23 and deviation detecting circuit 24. Before detecting by using 
diode sensor 17, computer 25 converts CAD format data stored in a magnetic 
tape 27, which has been transferred from computer aided design system 70, 
into a pattern data having a trapezoid format, for instance, and stores it 
in a magnetic disc memory 21. 
Circuit 22 reads out a portion of the pattern data in accordance with 
detected position data inputted by position detecting circuit 19 from 
magnetic disc memory 21, and produces a reference data used for judging 
circuit 23 and deviation circuit 24. Based on a difference between the 
reference data and detected data, judging circuit 23 produces data 
representing a discord among this data, and applies them to computer 25. 
Computer 25, in turn edits a group of data representing discord and stores 
this group as information concerning mask defects in a predetermined 
memory area of magnetic disc memory 21. 
Deviation detecting circuit 24 detects deviation quantities for each X and 
Y directions from the detected data and the reference data, and applies 
the quantities to circuit 22. Circuit 22, in turn compensates a portion of 
pattern data to be actually read out from magnetic disc memory 21 in 
accordance with the deviation quantities. 
Mask Drawing Apparatus (MD) 
FIG. 6 is a block diagram of mask drawing apparatus 102 as used in the 
present invention. In the right portion of FIG. 6, there is provided an 
electron beam drawing machine EBM which includes a vibration isolating 
support 50, mask drawing room 47, an electro-optical system EOS, and a 
mask reserving room 48. 
In mask drawing room 47, there is an X-Y table 49 on which a mask blank 73 
to be drawn upon is fixedly located. X-Y table 49 is movable to the 
directions of axes X and Y. 
Electro-optical system EOS comprises a cylinder 74 which provides an 
electron gun 41 for emitting an electron beam to mask 73 at the top 
portion of its inner side. 
Under electron gun 41 in cylinder 74, the emission strength of which is 
controlled by a power controller 51, there are mounted on a first 
condensing lens 42, a second condensing lens 73 and an objective lens 44. 
Strengths of each electric field near those lenses 42, 43 and 44 are 
controlled, respectively by signals from power controller 51. 
Between first condensing lens 42 and second condensing lens 42, there is 
mounted a blanking electrode 45, and also between second condensing lens 
42 and objective lens 44, there is mounted a deflection electrode 46. 
Blanking electrode 45 blanks the beam emitted from electron gun 41 so that 
it will not to reach the drawing area of mask blank 73 in accordance with 
a signal from a circuit 57 which reads out dot data defining the pattern 
to be drawn from drawing data producing unit 62. Deflection electrodes 46 
controlled by a deflection control circuit 56, deflects the electron beam 
for moving it to the direction of axis X and flying it back during one 
scanning, the width of beam movement on mask 73 corresponding to the width 
mentioned above in relating to diode sensor 17. Numeral 53 designates a 
driving mechanism for moving X-Y table 49 in the direction of the X and Y 
axes, thereby mask 73 on the table being moved in the fashion of raster 
scan. 
Numeral 54 designates a drive circuit for driving mechanism 53. Numeral 52 
designates a laser interferrometer connected to a position detecting 
circuit 55, which produces signals with respect to X and Y positions of 
mask 73 mounted on X-Y table 49. 
Drawing data producing unit 62 comprises a pattern data memory 60 which 
receives some groups of pattern data through a computer 64 and a direct 
memory pattern data through a computer 64 and a direct memory access unit 
(DMS) which operates to transfer pattern data from magnetic disc memory 68 
to memory 60, a converter 59 which converts unit pattern data defining one 
trapezoid figure into a group of dot pattern data, a dot pattern data 
memory 58, and a control unit 61 for controlling the operations of pattern 
data memory 60, DMA 63, converter 59, dot pattern memory 58 and circuit 57 
for smoothly executing pattern data conversion to dot pattern data and 
reading them out. 
Numeral 65 designates a control program necessary for operating a system of 
computer 64, and numeral 66 designates a format conversion program for 
converting CAD format data being stored in magnetic tape 69, which is 
produced by CAD system 70, into pattern data (EB format) stored in 
magnetic disc memory 68, which is used for drawing the mask 73. 
Numeral 67 designates an interface unit connected with computer 64, 
controller 61, deflection control circuit 56, drive circuit 54 and a 
synchronized signal producing unit 72 from which a clock signal for timing 
is applied to circuit 57, deflection control circuit 56 and position 
detecting circuit 55. Numeral 71 designates a console unit handled by an 
operator. 
The pattern data having EB format stored in magnetic disc memory 68 
comprises a number of the unit pattern data defining a trapezoid suitable 
for electron beam drawing machine EMB operated with a raster scanning 
mode. More detail of the pattern data and its conversion to dot pattern 
data is disclosed in the specification of Japanese patent laid open No. 
55-9433. 
Before drawing operation starts, a drawing start position on mask 73, a key 
marking position, the value of scaling factor and beam emission quantity 
are applied to computer 64 from console unit 71, so that computer 64 and 
its control program 65 define a diameter of the beam, beam current values, 
a deflection width, moving speeds of X-Y table 49 and a rate of division, 
then a mask drawing operation begins to draw. 
The arrangement of a mask inspection apparatus (MI) 104 and a mask drawing 
apparatus (MD) 102 have been described, and as shown in FIGS. 5 and 6, in 
memory 68 and memory 21, there are stored common or same pattern data 
having a trapezoid format which is called "EB format". 
In mask inspection apparatus 104, pattern data stored in memory 21 is 
converted into a modified dot pattern data as reference data applied to 
judging circuit 23, and in mask drawing apparatus 102, pattern data stored 
in memory 68 is converted into dot pattern data applying to 
electro-optical system EOS of electron beam drawing machine EBM. Both 
apparatuses provide circuit 22 or converter 59 for converting pattern data 
into dot pattern data, respectively. 
Circuit 22 and converter 59 execute substantially the same functions or 
operations from the point of view of data conversion. It is preferable 
that pattern data stored in memory 21 and memory 68 are the same data 
format, and that they are commonly used as described with reference to 
FIGS. 2, 3 and 4. 
The invention advantageously functions to commonly make use of the same 
memory, in which a pattern data is stored, for both of mask drawing and 
mask inspection apparatuses. 
The esssence of the invention, the technical idea of commonly making use of 
the memory, covers both of fashions for transferring the pattern data to a 
mask drawing apparatus and a mask inspection apparatus, the one 
corresponding to transfer the pattern data from physically the same memory 
device to the apparatuses respectively, as shown in FIGS. 2 and 4, and the 
other corresponding to transfer the pattern data from a plurality of the 
memory devices, between which the pattern data is transferred, to the 
apparatuses, as shown in FIG. 3. 
According to the invention, as data conversion system or process 7 shown in 
FIG. 1 is eliminated, it is advantageous for the users of mask drawing and 
mask inspection apparatuses, the process from mask drawing to mask 
inspection becomes short and simple, errors occurring in format conversion 
of the process are eliminated, and therefore chips of LSI circuits can be 
produced at lower cost and much faster than before. Moreover, in case that 
the circuit for converting pattern data into reference data in a mask 
inspection apparatus substantially equals to the converter of a mask 
drawing apparatus. It is advantageous that manufacturers of a mask 
inspection apparatus need not prepare programs necessary for format 
conversion because of commonly making use of a memory device storing 
pattern data therein. 
Though the mask inspection apparatus shown in FIG. 5 is provided with an 
optical scanning device, the invention is not limited to it, and also 
though the mask drawing and inspection apparatuses is provided with X-Y 
tables moving continuously to the direction of axis Y, as called "raster 
scanning", the invention is not limited to the raster scanning. In a 
short, the present invention is applicable to a combination of mask 
drawing and inspection apparatuses of the type which executes drawing by 
using dot pattern data for blanking beams (though not limited to electron 
beam), which is converted from pattern data, then produces measured data 
by scanning the drawn mask, and at the same time produces a reference data 
for comparing them each other for judging the existence of mask defects. 
Thus, while the present invention has been herein described in what is 
presently conceived to be the most preferred embodiments thereof, it will 
be understood to those in the art that many modifications may be made 
hereof within the scope and spirit of the present invention, which scope 
is to be accorded the broadest interpretation of the appended claims so as 
to encompass all equivalent methods and apparatuses.