Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2003-01-15
2004-11-02
Thompson, Craig A. (Department: 2813)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
Reexamination Certificate
active
06812155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention, in the field of microscopic processing technology for semiconductor fabrication and the like, relates to a pattern formation method, which forms a predetermined pattern in a resist film upon a wafer through exposure using phase-shift masks. Hereinafter, exposure using phase-shift masks is abbreviated as “phase-shift exposure”.
2. Description of the Related Art
In recent years, miniaturization in pattern dimensions have become increasingly necessary as achievements in high-speed and high levels of integration in semiconductor devices are made. As a result, design rules have become reduced to approximately half the exposure wavelength.
For example,
FIG. 8
shows optical contrast in the case where, for example, a 100 nm isolated line is exposed onto a photoresist layer through KrF excimer exposure (wavelength 248 nm) or ArF excimer exposure (wavelength 193 nm). The 100 nm isolated line is a line that has a plurality of linear pattern elements of width 100 nm arranged in parallel at equal intervals. Optical contrast is defined as (light intensity at pattern center−light intensity at pattern edge)÷(light intensity at pattern edge), whereby it is believed that a value of approximately 0.5 or more is necessary for resolving a pattern into a preferred shape. On the other hand, in formation of patterns with width of approximately 100 nm, pattern width is less than half the exposure wavelength. As can be seen from
FIG. 8
, in formation of patterns with microscopic widths to this degree, resolving into the preferred shape using a normal mask subjected to exposure techniques is extremely difficult since the optical contrast is smaller than 0.5. Thus, various “super resolution techniques” are under review. Among them, the “Levinson phase-shift mask” (see Japanese Patent Application Laid-open Sho 62-50811) is considered as the most promising technique in formation of patterns less than half the exposure wavelength since the optical contrast and resolution improving effects are significant.
FIG. 9A
to
FIG. 9C
are top views illustrating a pattern formation method through conventional phase-shift exposure, wherein
FIG. 9A
is a phase-shift mask used in a first exposure,
FIG. 9B
is a normal mask used in a second exposure, and
FIG. 9C
is a circuit pattern formed through these exposures. Width W
s
of the line patterns shown in
FIG. 9C
is 100 nm. Description thereof is based on these drawings hereinafter.
A phase-shift mask
40
shown in
FIG. 9A
is used in the first exposure. The phase-shift mask
40
is a positive type Levinson phase-shift mask, and has an L-shaped light shielding portion
421
b
and linear light shielding portions
421
a
. The phase-shift mask
40
has a phase-shifter
422
b
, which is formed adjacently to the L-shaped light shielding portion
421
b
, and phase-shifters
422
a
, which are alternately arranged in the spaces between the linear light shielding portions
421
a
. The region other than the L-shaped light shielding portion
421
b
, linear light shielding portions
421
a
, phase-shifter
422
b
and phase-shifters
422
a
of the phase-shift mask
40
is made to be a transmissive portion
423
. Since the phases of the exposure light that passes through the transmissive portion
423
do not change, “0” is given to the transmissive portion
423
in
FIG. 9A
; and since the exposure light that passes through the phase-shifters
422
a
and
422
b
changes in phase only by &pgr; (180), “&pgr;” is given. The phases of the exposing light that passes through the transmissive portion
423
adjacent to the shielding portions
421
a
and the exposing light that passes through the phase-shifters
422
a
differ precisely 180. During the first exposure, the photoelectric fields at the borders of the transmissive portion
423
with the phase-shifters
422
a
and
422
b
are completely neutralized, forming an image with an extremely sharp dark area. The dark area formed at the 0-&pgr; border is called a phase edge. The second exposure subsequently performed is exposure for preventing unnecessary dark areas including the phase edge from being resolved as resist patterns. In other words, using the normal mask
42
shown in
FIG. 9B
, all of the line pattern regions and L-shaped pattern regions formed through the first phase-shift exposure are shielded from the light so as to expose the remaining regions. In particular, the unnecessary dark area formed at the 0-&pgr; border is exposed to be eliminated. A circuit pattern
44
is then achieved upon a wafer
441
by executing a development procedure.
However, there are problems such as the following in a conventional pattern formation method through phase-shift exposure.
FIG. 10
shows what happens to dimensions (width W
s
) of a pattern to be actually formed in accordance with the distance between adjacent patterns (inter-pattern distance) W in the case where a line pattern where width W
s
is 100 nm is exposed by phase-shift exposure. As shown in
FIG. 10
, pattern dimensional accuracy drastically decreases due to affects of the optical proximity effect with the inter-pattern distance W equal to or less than 400 nm.
Based on a fixed value for the inter-pattern distance W, a pattern with inter-pattern distance W larger than the fixed value is defined as an isolated pattern
461
, and a pattern with inter-pattern distance W smaller than the fixed value is defined as a dense pattern
462
. Conventionally, as shown in
FIG. 9C
, the isolated pattern
461
with the large inter-pattern distance W and the dense pattern
462
with the small inter-pattern distance W have been simultaneously exposed with the same phase-shift mask
40
. At this time, should the isolated pattern
461
and the dense pattern
462
be exposed as line patterns with same dimensions, there have been problems where dimensional differences of the pattern actually formed significantly increase. For example, as shown in
FIG. 10
, if a pattern where width W
s
is 100 nm is exposed, a 40 nm dimensional difference between the pattern actually formed with the isolated pattern and dense pattern arises. Correcting (optical proximity correction) such large dimensional differences on the reticle side is extremely difficult.
Furthermore, with conventional phase-shift exposure, as shown in
FIG. 11
, there have been problems where pattern dimensions drastically thicken as defocus, that is wafer surface asperities, increases. Thus, pattern dimensions vary in response to the irregular structure of the wafer surface.
Moreover, as in
FIG. 12
, since asymmetry in +, − defocusing has occurred when spherical aberrations persist, there have been problems of dimensional accuracy significantly deteriorating. Asymmetry in +, − defocusing indicates that even if the absolute value of the plus defocus for a given point and the absolute value of the minus defocus for another point is the same, the pattern dimensions at these points do not match. By constructively utilizing phase information under highly coherent conditions for image formation, phase-shift exposure becomes extremely sensitive to optical parameters on that principle. Consequently, the exposure is extremely affected particularly by the effects of lens aberrations that emerge as phase errors during image formation.
Accordingly, the aim of the present invention is to provide a pattern formation method through phase-shift exposure, which improves dimensional accuracy by eliminating effects of defocus and spherical aberrations in addition to affects of the optical proximity effect.
SUMMARY OF THE INVENTION
The present invention is a pattern formation method, which forms a predetermined pattern in a resist film upon a wafer through exposure using phase-shift masks, characterized by using differing phase-shift masks in response to an inter-pattern distance, which is the distance between adjacent patterns, and exposing under respective adequate conditions for respective phase-shift mask exposures. For example, reducing
NEC Electronics Corporation
Thompson Craig A.
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