Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
2000-07-13
2003-02-04
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S005000, C430S396000
Reexamination Certificate
active
06514647
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photomask used in lithography of semiconductor processing, and a resist pattern formation method, a method of determining alignment accuracy and a method of fabricating a semiconductor device using the photomask.
In the photolithography of semiconductor processing, in order to prevent alignment shift between a lower pattern formed on a lower layer and an upper pattern formed on an upper layer, it is determined whether or not there is alignment shift between a first alignment accuracy determining mark formed on the lower pattern and a second alignment accuracy determining mark formed on a resist pattern used for forming the upper pattern. When the alignment shift of the second alignment accuracy determining mark from the first alignment accuracy determining mark is within an allowable range, the upper layer is etched by using the resist pattern to form the upper pattern. When the alignment shift of the second alignment accuracy determining mark from the first alignment accuracy determining mark is out of the allowable range, the resist pattern is generally formed once again.
Before describing a first conventional method in which a lower portion of a contact hole is formed in a lower interlayer insulating film and an upper portion of the contact hole communicated with the lower portion is formed in an upper interlayer insulating film, the necessity for forming the lower portion of the contact hole in the lower interlayer insulating film and the upper portion thereof in the upper interlayer insulating film will be described as the premise.
In accordance with development in the integration of semiconductor integrated circuits, it is desired to form, in an interlayer insulating film, an opening for a contact hole or a line pattern having a small opening size and a large depth, namely, a high aspect ratio. Therefore, techniques for forming an opening with a high aspect ratio, such as an etching gas and a plasma etching system that can etch the bottom of an opening with a high aspect ratio, have been developed.
A contact hole with a very high aspect ratio, however, cannot be dealt with by the currently developed dry etching technique. Specifically, when the aspect ratio is so high that ions included in plasma cannot reach the bottom of the contact hole, the bottom of the contact hole cannot be etched even by conducting dry etching over infinitive etching time. In other words, there is a limit aspect ratio at which the etching cannot be carried out even through the dry etching conducted over infinitive etching time. For example, in the currently employed dry etching technique, the limit aspect ratio is approximately 6. Specifically, when a contact hole has an opening size of 0.2 &mgr;m, the limit of the depth of the hole that can be dry etched is approximately 1.8 &mgr;m. Therefore, a contact hole having an opening size of 0.2 &mgr;m cannot be formed into a depth larger than 1.8 &mgr;m by the current etching technique.
On the other hand, in order to meet the demands for further refinement of semiconductor integrated circuits, it is desired to form a contact hole with a depth beyond the limit aspect ratio in an interlayer insulating film.
Therefore, the aforementioned method is required, in which an interlayer insulating film is dividedly deposited as a lower inter layer insulating film and an upper interlayer insulating film, and contact holes each having a depth below the limit aspect ratio are formed in the same position in the lower interlayer insulating film and the upper interlayer insulating film, so as to form one contact hole from the lower contact hole formed in the lower interlayer insulating film and the upper contact hole formed in the upper interlayer insulating film. In this case, the thicknesses of the lower and upper interlayer insulating films are set so that the aspect ratios of the contact holes respectively formed therein can be lower than the limit aspect ratio.
Now, the first conventional method will be described with reference to FIGS.
11
(
a
) through
11
(
c
) and
12
(
a
) through
12
(
c
). In each of FIGS.
11
(
a
),
11
(
c
) and
12
(
a
) through
12
(
c
), a portion on the right hand side of break lines corresponds to a main pattern region (element formation region) where line patterns and contact holes are to be formed, and a portion on the left hand side of the break lines corresponds to an alignment accuracy determining mark region where alignment accuracy determining marks are to be formed.
First, as is shown in FIG.
11
(
a
), a line pattern
12
of a metal line or a gate electrode is formed on an underlying insulating film
11
formed on a semiconductor substrate
10
. In this case, a first alignment accuracy determining mark
13
in a concave shape is formed in the line pattern
12
. Next, after depositing a lower interlayer insulating film
14
on the line pattern
12
, a first resist film is formed on the lower interlayer insulating film
14
, and the first resist film is exposed by using a photomask
15
and developed, thereby forming a first resist pattern
16
. In the first resist pattern
16
, a second alignment accuracy determining mark
17
in a convex shape having a smaller plane area than the first alignment accuracy determining mark
13
is formed in a position corresponding to the first alignment accuracy determining mark
13
.
Then, as is shown in FIG.
11
(
b
), it is determined whether or not there is alignment shift of the second alignment accuracy determining mark
17
from the first alignment accuracy determining mark
13
. In the determination of the alignment shift, the shapes of the line pattern
12
and the first resist pattern
16
can be recognized by observing the top face of the semiconductor substrate
10
with an optical measurement apparatus because the lower interlayer insulating film
14
is transparent in a visible radiation region. Accordingly, the distance in the X direction and the Y direction between the edges of the first alignment accuracy determining mark
13
and the second alignment accuracy determining mark
17
(i.e., the alignment shift) can be thus measured, so as to determine whether or not the alignment shift of the second alignment accuracy determining mark
17
from the first alignment accuracy determining mark
13
is within an allowable range.
When it is determined that the alignment shift of the second alignment accuracy determining mark
17
from the first alignment accuracy determining mark
13
is within the allowable range, the lower interlayer insulating film
14
is etched by using the first resist pattern
16
as a mask, so as to form a contact lower portion
19
by forming a lower portion
18
of a contact hole in the lower interlayer insulating film
14
and filling a first metal film within the lower portion
18
of the contact hole as is shown in FIG.
11
(
c
). In this case, in the alignment accuracy determining mark region, an opening is formed in a peripheral portion of the second alignment accuracy determining mark
17
in the lower interlayer insulating film
14
, namely, in a peripheral portion of the first alignment accuracy determining mark
13
, and hence, the first metal film
20
is filled within this opening.
Next, as is shown in FIG.
12
(
a
), after depositing an upper interlayer insulating film
21
on the lower interlayer insulating film
14
, a second resist film is formed on the upper interlayer insulating film
21
. Then, the second resist film is exposed by using the same photomask
15
and developed, thereby forming a second resist pattern
22
. Also in this case, in the second resist pattern
22
, a third alignment accuracy determining mark
23
in a convex shape with the same size as the second alignment accuracy determining mark
17
is formed.
Since the first metal film
20
is filled in the peripheral portion of the first alignment accuracy determining mark
13
as described above, however, the edge of the first alignment accuracy determining mark
13
cannot be recognized by observing the top fa
Hinogami Reiko
Nakagawa Hideo
Watanabe Hisashi
Huff Mark F.
Matsushita Electric - Industrial Co., Ltd.
Mohamedolla Saleha R.
Nixon & Peabody LLP
Studebaker Donald R.
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