Process for making photomask pattern data and photomask

Details Process for making photomask pattern data and photomask Process for making photomask pattern data and photomask

2001-05-14

2003-05-06

Smith, Matthew (Department: 2825)

Computer-aided design and analysis of circuits and semiconductor

Nanotechnology related integrated circuit design

Reexamination Certificate

active

06560767

ABSTRACT:

FIELD OF INDUSTRIAL APPLICATION
The present invention relates to a process of correction of design data for the production of photomask coping with miniaturization and high-density of semiconductor. Particularly, the present invention relates to a method for correcting original figure data used in the pattern exposure system for forming a pattern of photomask as to obtain the objective shape of pattern on a wafer.
BACKGROUND OF THE INVENTION
Recently, from a tendency for electric equipment to be made highly functional and lighter, thinner, shorter and smaller, it is being desired more and more that several LSI's typified by ASIC (application specific integrated circuit) are made highly integrated and highly functional. Namely, to realize the high function is desired for LSI such as ASIC by reducing the size of chip.
The process for forming semiconductor device is made through several steps in such a manner that figure data for forming photomask pattern (it is also called “pattern data” are made through function design, logical design, circuit design, layout design and others, a photomask is produced using the figure data, thereafter the pattern of photomask is transferred on a wafer by the pattern reduction exposure, so that the above-mentioned LSI such as ASIC is produced.
In general, a photomask is made through several steps in such a manner that pattern exposure is given to photosensitive resist disposed on the shielding film of a photomask substrate for (the shielding film of photomask substrate is also called “photomask blank”) using the above-mentioned figure data (“pattern data”) and by means of the electron beam pattern exposure system or the photo pattern exposure system projecting rays such as excimer wavelength, steps such as development and etching are made, by which a photomask is produced.
Namely, ionizing radiation is applied to given areas of photosensitive resist is coated on a shielding metallic thin film of photomask substrate provided on one side of glass substrate and dried, by means of the pattern exposure system, by which a latent image is formed. Then, the photosensitive resist having latent image is developed, by which a resist pattern with a desired shape is formed corresponding to the irradiation area of ionizing radiation. Thereafter, the metallic film is worked following the resist pattern by etching using the resist pattern as etching-proof resistance resist so that a photomask with a desired metallic film pattern is obtained.
In case of a pattern of photomask being transferred to a wafer by reduction exposure, a photomask is also called a reticule pattern.
When a pattern of photomask is transferred to a wafer by reduction exposure, a distortion of the shape of exposure called optical proximity effect is appeared. The reason because when a size of the shape of exposure (a size of pattern exposure to wafer) approaches wavelength of exposure light or becomes smaller than wavelength of light, exposure faithful to the shape of pattern of photomask becomes impossible by the phenomenon of diffraction so that the shape of pattern of photomask exposed to the wafer distortion is distorted on a wafer.
In a case where a pattern of photomask (the shape of part of photomask not transmitting light) has the shape as shown in FIG.
8
A(i), the shape formed on a wafer becomes as shown in FIG.
8
A(ii). Therefore, when it is desired to obtain the shape of pattern on a wafer as shown in FIG.
8
A(i), a pattern of photomask (the shape of part of photomask not transmitting light) is corrected as shown in FIG.
8
B(i) so that the shape of pattern formed on a wafer is made as shown in FIG.
8
B(ii). Such a correction made in consideration of the influence of diffraction of light is called OPC (Optical Proximity Correction).
Hereafter, as to figure data for forming a pattern of photomask, data not having the correction made in consideration of distortion (deformation) when producing a mask and when producing a wafer according to the circuit design is called original figure data of design data, or original figure data. Further, data having the correction made in consideration of distortion (deformation) when producing a mask and when producing a wafer is called correction figure data. In general, the process for carrying out the optical proximity correction given to original figure data is called the OPC process, and correction data in which original figure data is corrected through the optical proximity correction is also called the OPC process data. Figure data is also called pattern data Figure data for forming a pattern of photomask is formed according to various information, which is expressed in the X-Y coordinates.
Referring to
FIGS. 4 and 5
, a first conventional example of a method for generating correction figure data is explained. Further, referring to
FIGS. 6 and 7
, a second conventional example of a method for generating correction figure data is explained.
FIG. 4
is a flow sheet of a first conventional example for generating correction figure data. FIG.
5
A(i) and FIG.
5
B(i) show an example of original figure data. In case of the example shown in FIG.
5
A(i), correction is needed for corners of figure. In case of the sample shown in
FIG. 5
B(i), correction is needed for parts of figure in which the parts are arranged sparsely.
FIG.
5
A(ii) and FIG.
5
B(ii) show patterns in which correction figures are generated for original figure data shown in FIG.
5
A(i) and FIG.
5
B(i) according to the first conventional method, respectively. FIG.
5
A(iii) and FIG.
5
B(iii) show patterns transferred to wafers (hereafter called “wafer patterns”) through photomasks having the shapes of pattern shown in FIG.
5
A(ii) and FIG.
5
B(ii), respectively.
FIG. 6
is a flow sheet of the second conventional method for generating correction figure data. FIG.
7
A(i) and FIG.
7
B(i) show original figure data, respectively. FIG.
7
A(ii) and FIG.
7
B(ii) show patterns in which correction figures are generated according to the second conventional method. FIG.
7
A(iii) and
FIG. 7B
(iii) show patterns transferred to wafers through photomasks produced by patterns shown in FIG.
7
A(ii) and FIG.
7
B(ii), respectively.
Hereafter, to make this description plain, original figure data shown in FIG.
5
A(i) and FIG.
5
B(i) are made the same as original figure data shown in FIG.
7
A(i) and FIG.
7
B(i).
Further, “S
410
” to “S
490
” in FIG.
4
and “S
610
” and “S
670
” in
FIG. 6
designate steps of process.
The first conventional method is a method for determining the correction figure data for optical proximity correction according to the information on deformation generated when original figure data is transferred to a wafer by optical proximity effect.
The production of photomask is carried out using figure data in which only the optical proximity correction process (OPC process) is given to original figure.
This method is based on the assumption that the faithfulness or correctness of pattern formed on a photomask to original pattern can be kept. Namely, slight difference is generated between original figure data and a pattern formed on a photomask in the production. However, heretofore, it was thought that patterns to be formed are not small so far so that the influence on quality brought about by the difference between the two can neglected.
In this case, patterns (figures) determined according to the information on deformation when forming original figure patterns by optical proximity effect obtained in advance, in this example, a figure of square is generated at corners of original figure data shown in FIG.
5
B(i). On the other hand, the figures for correcting the phenomenon that width of parts of original figure data as shown in FIG.
5
B(i) in which the parts are disposed sparsely becomes thin are generated.
When a pattern is transferred to a wafer through the photomask produced using pattern data with the above-mentioned figures for correcting to the phenomenon, patterns (figures) shown in FIG.
5
A(iii) and FIG.
5
B(iii) are formed on a wafer.
However

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