Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-12-09
2001-10-23
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06306547
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photomask employed in manufacturing a semiconductor element and a manufacturing method thereof, and to an exposure method using the photomask.
BACKGROUND OF THE INVENTION
A conventional manufacturing method of a semiconductor element uses a technique, in which, as shown in FIGS.
2
(
a
) and
2
(
b
), a through hole
61
and a wire groove are formed in an inter-layer insulating film
6
covering a bottom wire layer
7
, so that a wire material is embedded therein.
As shown in FIG.
2
(
b
), the inter-layer insulating film
6
has (1) a through hole area
23
which corresponds to the through hole
61
, in which the inter-layer insulating film
6
is completely removed, and (2) a half area
22
in which the film thickness of the inter-layer insulating film
6
is reduced to approximately half in comparison with a surrounding area (which is referred to as a basic area
21
, hereinafter). The half area
22
and basic area
21
form a step-wise shape
62
as shown in FIG.
2
(
a
). The step-wise shape
62
is formed in the inter-layer insulating film
6
by a combination of prior arts, examples of which include the following two methods.
The first method is performed by means of half etching. In this method, as shown in FIG.
11
(
a
), the half area
22
(see FIG.
2
(
b
)) is exposed to light (indicated by arrows in the drawing) and developed on a wafer including a resist
5
, the inter-layer insulating film
6
, and the bottom wire layer
7
, which are layered in vertical direction from top to bottom.
Next, as shown in FIG.
11
(
b
), the half etching treatment is applied to the half area
22
from which the resist
5
has been removed when developed, and the inter-layer insulating film
6
is etched to approximately half the initial thickness, whereby the step-wise shape
62
is formed.
Next, as shown in FIG.
11
(
c
), after the resist
5
is applied again, the through hole area
23
(see FIG.
2
(
b
)) is exposed to light (indicated by arrows in the drawing) and developed. Then, as shown in FIG.
11
(
d
), the etching treatment is applied to the inter-layer insulating film
6
in the through hole area
23
, whereby the through hole
61
is formed.
The second method is performed by means of half exposure. In this method, half exposure to light (indicated by arrows in the drawing), by which the thickness of the resist
5
is reduced to approximately half the initial thickness, is effected on the half area
22
of a wafer of the identical structure as that shown in FIG.
11
(
a
). Then, additional exposure is effected on the through hole area
23
to compensate an underexposure. Consequently, as shown in FIG.
12
(
b
), a resist hole
101
and a resist step
102
are formed in the resist
5
.
Then, as shown in FIG.
12
(
c
), the inter-layer insulating film
6
in the through hole area
23
is removed by means of etching, whereby the through hole
61
is formed. Then, as shown in FIG.
12
(
d
), the resist
5
in the half area
22
is removed (by means of ashing). Finally, as shown in FIG.
12
(
e
), the step-wise shape
62
is formed in the inter-layer insulating film
6
by the half etching process.
Alternatively, available as a method of forming the step-wise shape
62
is a technique that employs an exposure and development process using a photomask furnished with transmittivity levels, in other words, a photomask having a blocking portion, a transflecting portion, and a transmitting portion.
Such a technique is disclosed in, for example, {circle around (1)} Japanese Laid-open Patent Application No. 18351/1988 (Japanese Official Gazette, Tokukaisho No. 63-18351, published on Jan. 26, 1988), {circle around (2)} Japanese Laid-open Patent Application No. 27636/1994 (Japanese official Gazette, Tokukaihei No. 6-27636, published on Feb. 4, 1994, and {circle around (3)} Japanese Laid-open Patent Application No. 49410/1995 (Japanese Official Gazette, Tokukaihei No. 7-49410, published on Feb. 21, 1995).
In the technique of the disclosure {circle around (1)}, a translucent film made of chromium oxide (CrO) is used as the transflecting portion, and a chromium (Cr) film is used as the blocking portion. In the technique of the disclosure {circle around (2)}, a silicon dioxide film mixed with a light-absorbing material is used as the transflecting portion, and a triple-layer blocking film having a structure of chromium oxide/chromium/chromium oxide (CrO/Cr/CrO) is used as a blocking film. Further, in the technique of the disclosure {circle around (3)}, the blocking portion and transflecting portion are formed in the photomask made of a chromium compound by giving different thicknesses to the chromium compound film.
However, each of the foregoing techniques has the following problems.
The first method as a combination of prior arts is popular, but a series of processes, including the resist apply process, exposure and development process and etching process, has to be repeated twice. Thus, this method involves quite a large number of processes. For this reason, not only throughput, but also yield of devices is reduced, because dust adheres to the semiconductor element more frequently.
In the second method, the exposure and development process has to be repeated twice, but the other processes are performed only once, thereby involving fewer processes in comparison with the first method. However, because two photomasks are used in the exposure and development process, the exposure pattern of the half area
22
and that of the through hole area
23
have to be aligned accurately.
The accuracy of alignment of the exposure patterns is determined by accuracy of alignment of each photomask by means of a stepper and accuracy of relative positions of the two photomasks with respect to each other (overlapping accuracy of the photomasks). Because each accuracy has to be quite high, the accuracy of alignment can be a de-stabilizing factor in the exposure and development process.
As has been discussed, the foregoing methods demand repetitive exposure and development or highly accurate alignment of the photomasks, which complicates a process of forming the step in the inter-layer insulating film
6
.
In contrast, the techniques in the disclosures {circle around (1)} through {circle around (3)} use a single photomask including the transflecting portion in addition to the blocking portion and transmitting portion. Hence, the resist step
102
as shown in FIG.
12
(
b
) can be formed in the resist
5
by effecting exposure and development once. Consequently, the step-wise shape
62
can be formed in the inter-layer insulating film
6
without repeating exposure and development or aligning the photomasks accurately, thereby shortening and simplifying the step forming process.
However, as far as a specific arrangement of the transmitting portion and transflecting portion formed in a single photomask is concerned, the techniques in the disclosures {circle around (1)} through {circle around (3)} teach the transmittivity levels, but remain silent about giving a phase difference to the transflecting portion with respect to the transmitting portion.
The through holes
61
and wire grooves formed in the semiconductor element are so minute that, in order to transfer such a minute exposure pattern accurately onto the resist
5
through the photomask having the transmittivity levels, a phase difference of the transflecting portion with respect to the transmitting portion has to be controlled. For this reason, the techniques in the disclosures {circle around (1)} through {circle around (3)} share a problem that the resist step
102
can not be formed in the resist
5
as desired in a reliable manner.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide (1) a photomask, by which a resist step is formed in a resist accurately with transmittivity and a phase difference of a transflecting portion with respect to a transmitting portion being taken into consideration; (2) a manufacturing method of the photomask; and (3) an exposure m
Nixon & Vanderhye P.C
Rosasco S.
Sharp Kabushiki Kaisha
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