Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-07-06
2004-03-09
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S022000, C430S030000
Reexamination Certificate
active
06703168
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a pattern-exposure photomask for use in manufacturing semiconductor devices or liquid crystal display devices, a method for producing the same, and a patterning method using the photomask, and also relates to a method for producing photomask pattern layout, and a method for producing mask-writing data.
BACKGROUND ART
In recent years, a large-scale integrated circuit (hereinafter, referred to as LSI) implemented with a semiconductor has been increasingly reduced in size. As a result, a feature error or dimensional error between a mask pattern and a produced pattern (e.g., a resist pattern formed by pattern transfer for a resist film) have been increasingly regarded as important in a lithography process, one of the LSI manufacturing processes.
Moreover, reduction in pattern dimension in the LSI has reached about the resolution limit defined by a wavelength of a light source (hereinafter, referred to as wavelength &lgr;), a numerical aperture of a projection optical system of an aligner (hereinafter, referred to as numerical aperture NA), and the like. As a result, a manufacturing margin associated with the yield in LSI manufacturing, e.g., a depth of focus, has also been significantly reduced.
In a conventional patterning method, a resist pattern having a prescribed feature is formed as follows: a light-shielding pattern of a prescribed feature, i.e., a mask pattern, is formed on a transparent substrate using a light-shielding film of a metal such as chromium. Then, a wafer having a resist film applied thereto is exposed to light using the transparent substrate having the mask pattern thereon as a mask, so that light intensity distribution having a profile similar to the mask pattern feature is projected to the resist film. Thereafter, the resist film is developed, whereby the resist pattern having the prescribed feature is produced.
A reduction projection aligner is generally used in such a patterning method as described above. For patterning, the reduction projection aligner conducts reduction projection exposure for a resist film of a photosensitive resin formed on a wafer, i.e., a substrate, by using a transparent substrate including a mask pattern with the dimension of a desired pattern magnified several times, i.e., by using a photomask.
FIG.
32
(
a
) shows an example of a pattern whose minimum dimension is sufficiently larger than the resolution. FIG.
32
(
b
) shows the simulation result of light intensity distribution projected to, e.g., a resist film upon forming the pattern of FIG.
32
(
a
) using a conventional photomask.
More specifically, when the numerical aperture NA is 0.6 and the wavelength &lgr; is 0.193 &mgr;m, the resolution is about 0.13 &mgr;m. However, the minimum dimension of the pattern of FIG.
32
(
a
) is about 0.39 &mgr;m (about three times the resolution). The conventional photomask has a mask pattern having the dimension of the pattern of FIG.
32
(
a
) magnified by the magnification M of the aligner (an inverse number of a reduction ratio). In this case,. as shown in FIG.
32
(
b
), the implemented light intensity distribution has a profile similar to the feature of the pattern of FIG.
32
(
a
), i.e., the mask pattern. Note that FIG.
32
(
b
) shows the light intensity distribution using contour lines of the relative light intensity in a two-dimensional relative coordinate system (i.e., the light intensity calculated with the exposure light intensity being regarded as 1).
FIG.
33
(
a
) shows an example of a pattern whose minimum dimension corresponds to about the resolution. FIG.
33
(
b
) shows the simulation result of light intensity distribution projected to, e.g., a resist film upon forming the pattern of FIG.
33
(
a
) using a conventional photomask.
More specifically, when the numerical aperture NA is 0.6 and the wavelength &lgr; is 0.193 &mgr;m, the resolution is about 0.13 &mgr;m. The minimum dimension of the pattern of FIG.
33
(
a
) is also about 0.13 &mgr;m. The conventional photomask has a mask pattern having the dimension of the pattern of FIG.
33
(
a
) magnified by the magnification M. In this case, as shown in FIG.
33
(
b
), the implemented light intensity distribution is significantly distorted from the profile similar to the feature of the pattern of FIG.
32
(
a
), i.e., the mask pattern. Note that FIG.
33
(
b
) also shows the light intensity distribution using contour lines of the relative light intensity in a two-dimensional relative coordinate system.
More specifically, as the minimum dimension of the pattern is reduced to about the resolution, the line width of the mask pattern on the photomask is also reduced. Therefore, the exposure light is likely to be diffracted when passing through the photomask. More specifically, as the line width of the mask pattern is reduced, the exposure light is likely to reach the backside of the mask pattern. As a result, the mask pattern cannot sufficiently shield the exposure light, making it extremely difficult to form a fine pattern.
In order to form a pattern having a dimension equal to or smaller than about the resolution, H. Y. Liu et al. proposes a patterning method (first conventional example) (Proc. SPIE, Vol. 3334, P.2 (1998)). In this method, a light-shielding pattern of a light-shielding film is formed on a transparent substrate as a mask pattern, as well as a phase shifter for inverting the light transmitted therethrough by 180 degrees in phase is provided in a light-transmitting region (a portion having no light-shielding pattern) of the transparent substrate. This method utilizes the fact that a pattern having a dimension equal to or smaller than about the resolution can be formed by the light-shielding film located between the light-transmitting region and the phase shifter.
Hereinafter, the patterning method according to the first conventional example will be described with reference to FIGS.
34
(
a
) to (
d
).
FIG.
34
(
a
) is a plan view of a first photomask used in the first conventional example, and FIG.
34
(
b
) is a cross-sectional view taken along line I—I of FIG.
34
(
a
). As shown in FIGS.
34
(
a
) and (
b
), a light-shielding film
11
is formed on a first transparent substrate
10
of the first photomask, and first and second openings
12
and
13
are formed in the light-shielding film
11
such that a light-shielding film region
11
a
having a width smaller than (resolution×magnification M) is interposed therebetween. The first transparent substrate
10
is recessed under the second opening
13
so as to provide a phase difference of 180 degrees between the light transmitted through the first transparent substrate
10
through the first opening
12
and the light transmitted through the first transparent substrate
10
through the second opening
13
. Thus, the portion of the first transparent substrate
10
corresponding to the first opening
12
serves as a normal light-transmitting region, whereas the portion of the first transparent substrate
10
corresponding to the second opening
13
serves as a phase shifter. Therefore, a pattern having a desired line width equal to or smaller than about the resolution can be formed by the light-shielding film region
11
a
located between the first and second openings
12
and
13
.
FIG.
34
(
c
) is a plan view of a second photomask used in the first conventional example. As shown in FIG.
34
(
c
), a light-shielding pattern
21
of a light-shielding film is formed on a second transparent substrate
20
of the second photomask.
In the first conventional example, a desired pattern is formed by combination of a line pattern formed by the light-shielding film region
11
a
of the first photomask of FIG.
34
(
a
) and a pattern formed by the light-shielding pattern
21
of the second photomask of FIG.
34
(
c
).
More specifically, in the first conventional example, a substrate having a positive resist film applied thereto is exposed to light using the first photomask of FIG.
34
(
a
). Then, the substrate is adjusted in position so that a desired pattern is
Huff Mark F.
Matsushita Electric - Industrial Co., Ltd.
Sagar Kripa
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