Radiation imagery chemistry: process – composition – or product th – Plural exposure steps
Reexamination Certificate
2002-04-29
2004-10-05
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Plural exposure steps
C430S005000, C430S030000, C430S396000, C716S030000, C716S030000, C716S030000
Reexamination Certificate
active
06800428
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of generating and a system of generating an exposure pattern for a lithography process used for semiconductors, liquid crystal substrates and printed boards, and more particularly to an exposure pattern generation method and an exposure pattern generation system which allows creating micro-patterns by a low technology stepper machine, such as an i-line, using a plurality of reticles or mask substrates.
2. Description of the Related Art
As the size of semiconductor devices decreases and precision thereof increases, micro-patterns must be created on a wafer at a required precision to satisfy the device characteristics. Therefore a reduction in size and an increase in precision are demanded for a photo mask (hereafter reticle) used in the wafer exposure process as well. Methods to create micro-patterns on a wafer at high precision are diversifying, and the price of reticles and the cost of aligners are increasing accordingly.
As a method of creating conventional micro-patterns (e.g. a 200 nm or less design rule), performing OPC processing (Optical Proximity Correction), where the exposure pattern is corrected considering the proximity exposure effect when the design data is converted to the format of the electron beam aligner to create exposure pattern data, and generating patterns by a stepper machine with a KrF excimer laser beam (248 nm) or an ArF excimer laser beam (193 nm) using a phase shift mask, have been proposed.
However, such conventional methods are not sufficient solutions since the data processing for OPC processing takes time, the cost of phase shift masks is high, and a stepper machine with a KrF or ArF excimer laser beam must be newly installed.
As a lithography method which allows the generation of micro-patterns using a conventionally popular i-line (365 nm) stepper machine, creating micro-patterns by a plurality of times of the lithography steps using a plurality of (e.g. two) reticles, has been proposed. For example, “wavelength-independent optical lithography” in J. Vac. Sci, Technol. B 18 (1), January/February 2000, discloses creating micro-patterns, executing exposure, developing and etching twice using two reticles, and creating micro-patterns by the composite pattern of these two reticles.
FIGS. 1A
to
1
C are diagrams depicting a conventional general lithography step. This lithography step comprises an exposure process (
FIG. 1A
) where light hv is irradiated onto a resist layer
4
coated on the patterning target layer
3
of the wafer substrate
2
using the reticle
1
which has the light transmission hole Pa, a resist development step (FIG.
1
B), and an etching step using the resist as a mask (FIG.
1
C). When the light transmission hole Pa becomes very small, the resist
4
cannot be developed to be a shape with the same pattern width a1 as the light transmission hole Pa. This is because light is out-of-focus, and resist cannot be finely processed by a stepper using such a long wavelength light as an i-line. As a result, the final pattern
6
to be created on the patterning target layer
3
tends to have a pattern width smaller than the pattern width a1 of the reticle
1
.
FIGS. 2A
to
2
F are diagrams depicting the wavelength-independent lithography step which is proposed by the above mentioned article. In this lithography step, exposure, development and etching are performing with a reticle A, which has a pattern Paa when a micro-pattern Pa is enlarged in a first direction, and a reticle B, which has a pattern Pab when the micro-pattern Pa is enlarged in a second direction respectively, so that the micro-pattern Pa is created by a composite of the reticles A and B. In exposure using the reticle
1
having the micro-pattern Pa, the resist cannot be patterned accurately because the long wavelength light, such as visible light, is out-of-focus, but in the case of exposure using the reticles A and B, which have patterns when the micro-pattern Pa is enlarged respectively, the resist can be patterned accurately even with long wavelength light.
As
FIG. 2A
shows, a protective layer
10
, such as oxide film, and a resist
4
A, are created on the pattern target layer
3
on the wafer
2
, and in the first exposure, the first reticle
1
A, which has a pattern Paa when the processing target pattern Pa is enlarged to the upper left direction, is used for exposure (FIG.
2
A). And this resist
4
A is developed and the resist
4
A is patterned. Since the transmission hole Paa is not a micro-pattern, light does not become out-of-focus during exposure, and the pattern Paa can be transferred onto the resist
4
A accurately. The protective layer
10
is etched using this resist
4
A as a mask (FIG.
2
C). The width b1 of the pattern created on the protective layer
10
is sufficiently larger than the width a1 of the processing target pattern Pa.
Then the resist
4
B is created on the protective layer
10
again, and a second exposure is executed. In the second exposure, the second reticle
1
B, which has a pattern Pab when the processing target pattern Pa is enlarged to the lower right direction, is used for exposure (FIG.
2
D). When the resist
4
B is developed and the resist
4
B is patterned, the pattern becomes a pattern which partially overlaps with the pattern on the protective layer
10
, created after the first exposure step (FIG.
2
E). This pattern width b2 is also sufficiently larger than the width a1 of the processing target pattern PA. Finally, using the pattern of the protective layer
10
and the pattern of the resist
4
B as a mask, the patterning target layer
3
is etched (FIG.
2
F). As a result, the processing target pattern Pa is created on the patterning target layer
3
by a composite pattern, where the enlarged pattern Paa of the reticle
1
A and the enlarged pattern Pab of the reticle
1
B are overlapped.
FIGS. 3A and 3B
are diagrams depicting the generation methods for two reticle patterns to be used for the lithography step shown in FIG.
2
. As
FIG. 3A
shows, the pattern of the reticle A, which is the first reticle, is an enlarged pattern Paa, where the left edge and the top edge of the processing target pattern Pa are extended. And as
FIG. 3B
shows, the pattern of the reticle B, which is the second reticle, is an enlarged pattern Pab, where the right edge and the bottom edge of the processing target pattern Pa are extended. The composite pattern where the patterns Paa and Pab of the reticles A and B overlap becomes the processing target pattern Pa.
Exposure and development are executed using the two reticles which have enlarged patterns, so a micro-pattern can be created using an i-line-based low technology stepper machine. However, the exposure, development and etching steps must be executed twice.
FIGS. 4A
to
4
C are diagrams depicting a problem of the above mentioned lithography method. This example is the case when the above mentioned lithography method is applied to four micro-patterns Pa, Pb, Pc and Pd, which are longer in the longitudinal direction, wherein the patterns Pb and Pc, out of the four micro-patterns, are close to each other. In the case of a micro-pattern which is longer in the vertical direction, the pattern of the reticle A becomes the enlarged patterns Paa, Pba, Pca and Pda, where the left edges are extended, as shown in
FIG. 4A
, and the pattern of the reticle B becomes the enlarged patterns Pab, Pbb, Pcb and Pdb, where the right edges are extended, as shown in FIG.
4
B.
In this case, the gray patterns where both patterns overlap in
FIG. 4
become the processing target micro-patterns Pa, Pb, Pc and Pd, but since the patterns Pb and Pc are close to each other, the enlarged patterns Pca and Pbb of these patterns partially overlap, and the finally created patterns include the error pattern Px, which is created between the micro-patterns Pb and Pc, as
FIG. 4C
shows.
To prevent the generation of this error pattern Px, the degree of enlargement when the reticles A and B are created is decreased, but then, t
Aiso Kiyokazu
Kawaguchi Tomoaki
Okada Tomoyuki
Omata Taketoshi
Sugawa Kazuya
Fujitsu Limited
Huff Mark F.
Sagar Kripa
LandOfFree
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