Pattern formation method

Details Pattern formation method Pattern formation method

1998-09-25

2002-01-22

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C430S313000, C430S323000

Reexamination Certificate

active

06340557

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a pattern formation method, and more particularly, it relates to a method of forming a pattern out of an etching target film formed on a semiconductor substrate by conducting dry etching on the etching target film by using, as a mask, a patterned photosensitive film formed on the etching target film with an anti-reflection coating of an organic material disposed therebetween.
In accordance with downsizing of a system using complicated semiconductor integrated circuits, it has become very difficult to transfer a complicated circuit onto a small chip by pattern lithography using a patterned photosensitive film as a mask. This is for the following reason: As the wavelength of an energy beam irradiating an etching target film is shortened, the reflectance of the energy beam is increased. Therefore, the energy beam is affected by an irregular step shape of the photosensitive film so as to be reflected in irregular directions after passing through the photosensitive film. As a result, an unnecessary portion (i.e., a portion that should not be irradiated with the energy beam) is exposed in the photosensitive film. This leads to a large number of artificial defects and dimensional variation in a pattern formed by the lithography.
As a countermeasure, it is proposed that an anti-reflection coating for absorbing the energy beam is formed below the photosensitive film so as to prevent the energy beam from being reflected in the irregular directions after passing through the photosensitive film.
Now, a conventional pattern formation method using an anti-reflection coating will be described with reference to FIGS.
4
(
a
) and
4
(
b
).
As is shown in FIG.
4
(
a
), an anti-reflection coating
3
of an organic material for absorbing an energy beam is deposited on an etching target film
2
formed on a semiconductor substrate
1
, and a photosensitive film is then deposited on the anti-reflection coating
3
. Next, the photosensitive film is irradiated with an energy beam through a mask, and an exposed or unexposed portion of the photosensitive film is removed by using a developer, thereby forming a patterned photosensitive film
4
out of the exposed or unexposed portion. Subsequently, the anti-reflection coating
3
is dry etched by using the patterned photosensitive film
4
as a mask, thereby removing an area of the anti-reflection coating
3
corresponding to an opening of the patterned photosensitive film
4
.
Next, as is shown in FIG.
4
(
b
), the etching target film
2
is dry etched by using the patterned photosensitive film
4
as a mask, and the anti-reflection coating
3
and the photosensitive film
4
are then removed. In this manner, a pattern
2
A of the etching target film
2
is formed on the semiconductor substrate
1
.
When the pattern
2
A is formed in the aforementioned manner, the energy beam having passed through the photosensitive film
4
is absorbed by the anti-reflection coating
3
disposed between the etching target film
2
and the patterned photosensitive film
4
. Accordingly, even when the photosensitive film
4
has an irregular step shape, the photosensitive film
4
can be prevented from being exposed to irregularly reflected light. As a result, the pattern
2
A of the etching target film
2
can be dimensionally accurately formed.
However, a reaction product
5
is generated on an interface between the anti-reflection coating
3
and the photosensitive film
4
as is shown in FIG.
4
(
a
), so that the reaction product
5
remains on the etching target film
2
after removing the anti-reflection coating
3
and photosensitive film
4
.
Thereafter, in the dry etching of the etching target film
2
by using the patterned photosensitive film
4
as a mask, the reaction product
5
remaining on the etching target film
2
serves as a mask. Accordingly, as is shown in FIG.
4
(
b
), a residue
6
of the etching target film
2
can be disadvantageously formed in an area to be etched (i.e., a space area) in the etching target film
2
or a pattern wall
2
a
of the etching target film
2
required to be vertical can be formed in an irregular shape. In particular, the residue
6
derived from the reaction product
5
has a very small size of 0.1 &mgr;m or less, and is a specific residue basically different from a residue formed due to insufficient conditions for the dry etching of the etching target film
2
(for example, a residue having a size of 0.2 &mgr;m or more).
Also, the residue
6
is generated uniformly without being affected by the aperture ratio of the pattern of the photosensitive film
4
, namely, regardless of the density of the pattern. Accordingly, the residue
6
is formed also in a space between patterns formed at a high density.
Therefore, a method of removing the reaction product
6
generated on the interface between the anti-reflection coating
3
and the photosensitive film
4
together with the anti-reflection coating through the dry etching of the anti-reflection coating
3
is considered, but this method is not effective as a method of forming a pattern of the etching target film for the following reason: In the dry etching of the anti-reflection coating
3
by using the patterned photosensitive film
4
as a mask, a larger part of the anti-reflection coating
3
is preferably removed while a smaller part of the patterned photosensitive film
4
is preferably removed. However, both the anti-reflection coating
3
and the photosensitive film
4
are made from organic materials, and hence, they have very similar dry etching characteristics (such as an etching rate). Accordingly, when the anti-reflection coating
3
is dry etched under conditions where the patterned photosensitive film
4
can be less removed through the dry etching, large parts of the reaction product
5
and the anti-reflection coating
3
remain on the etching target film
2
. In contrast, when the anti-reflection coating
3
is dry etched under conditions where the reaction product
5
cannot remain, the patterned photosensitive film
4
is also removed through the dry etching and cannot work as a mask. In addition, even when the dry etching is actually conducted so as to remove the reaction product
5
without considering the masking function of the photosensitive film
4
(for example, by elongating the etching time or the like), the residue
6
cannot be reduced.
Furthermore, when a dry etching process in which a deposition is formed on the wall of the anti-reflection coating
3
is adopted so as to improve the dimensional controllability on the anti-reflection coating
3
, the deposition peeled off from the wall of the anti-reflection coating
3
can be easily adhered onto the etching target film
2
. Therefore, the deposition works as a mask, resulting in forming the residue
6
of the etching target film
2
.
When the residue
6
of the etching target film
2
remains on the semiconductor substrate
1
or when the pattern wall
2
a
of the etching target film
2
is formed in an irregular shape, the following problems are caused:
In the case where the etching target film
2
is made from a conductive material such as polysilicon, wire patterns formed in the same conductive layer in a resultant semiconductor integrated circuit device can be electrically connected with each other through the conductive residue
6
. Alternatively, a conductive layer formed on the semiconductor substrate
1
can be electrically connected through the conductive residue
6
with a wire pattern formed on the conductive layer with an interlayer insulating film sandwiched therebetween. Accordingly, a leakage current flows between the wire patterns or between the conductive layer and the wire pattern. As a result, the semiconductor integrated circuit device can be disadvantageously degraded in its characteristic or yield.
FIG. 5
is an enlarged view of an area surrounded with a dashed line in FIG.
4
(
b
). As is shown in
FIG. 5
, a gate electrode
7
of a polysilicon film corresponding to the etching target film
2
is form

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