Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-12-28
2002-04-16
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S694000, C438S704000, C438S745000, C438S756000, C438S906000
Reexamination Certificate
active
06372650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of cleaning a substrate and to a method of manufacturing a semiconductor device and, more particularly, to a method of cleaning a substrate and to a method of manufacturing a semiconductor device removing contaminants after working a surface of a substrate by chemicals etc., or treating the surface of the substrate by the chemicals, etc. prior to film formation.
2. Description of the Prior Art
In recent years, the prior art has mainly used a mixed solution consisting of sulfuric acid, hydrochloric acid, ammonium, hydrogen peroxide, etc. to clean a silicon wafer. Since metals and organic matters are removed, this cleaning method is effective.
A cleaning method using various steps to manufacture semiconductors in the prior art will now be explained with reference to
FIGS. 1A and 1B
which are sectional views showing steps of cleaning a surface of a semiconductor substrate
1
after trench grooves
3
have been formed in the semiconductor substrate
1
.
As shown in
FIG. 1A
, the trench grooves
3
are first formed in the semiconductor substrate
1
using a resist film
2
as a mask. Then, the resist film
2
is removed by a resist removing liquid and, as shown in
FIG. 1B
, the semiconductor substrate
1
in which the trench grooves
3
are formed is exposed to a liquid such as sulfuric acid to remove contaminants such as resist removing liquid.
In the second step, as shown in
FIG. 2A
, a writing pattern
13
is first formed on an underlying insulating film
12
on a semiconductor substrate
11
by using the resist film
14
as a mask. Then, as shown in
FIG. 2B
, the resist film
14
is removed by the resist moving liquid. Then, as shown in
FIG. 2C
, an insulating film
15
is formed by the CVD method to cover the wiring
13
formed on the underlying insulating film
12
.
In the third step, as shown in
FIG. 3A
, a surface of the underlying insulating film
22
on semiconductor substrate
21
is first cleaned by a liquid, e.g. sulfuric acid, etc. Then, as shown in
FIG. 3B
, a silicon containing insulating film
23
is deposited on the underlying insulating film
22
by the thermal CVD method using a reaction gas including TEOS (for example, N
2
is employed as the carries gas) and ozone (which is included in the 0
2
at the predetermined concentration).
In the case of FIG.
1
A and
FIG. 1B
, in recent years, with the progress of miniaturization of semiconductors, the opening of such a groove has become narrower and thus the ratio of depth to width of opening of the groove
3
(this ratio is called an aspect ratio) has become higher. Such an aspect ratio, at most, is five to eight. In the case of a groove which has a narrow opening width but a deep depth, in the chemical processing shown in
FIG. 1B
, it becomes difficult for the chemicals to reach the bottom of groove
3
and then difficult for the chemicals to be replaced by a pure water wash once the chemicals have entered into the groove. Thus, it is extremely difficult to completely clean the bottom and the side surfaces of the groove
3
.
In the case of
FIGS. 2A-2C
, when the insulating film
15
is formed by the CVD method to cover the wiring
13
after surface treatment, it is difficult to deposit the insulating film
15
between the wire portions. As a result, as shown in
FIG. 2C
, deep hollows are sometimes produced between the wirings
13
. If a conductive film is used to form an additional layer of wiring on insulating film
15
, the conductive film cannot be satisfactorily deposited on such concave portions and the conductive film entering into the concave portions cannot be removed. If chemicals such as EKC (Trade name of EKC Company) is employed as the resist removing liquid, the growth rate of the SiO
2
film
15
is extremely slow on the concave surface portions when the film is formed by the CVD method, after the pre-treatment, so that the concave portions cannot be covered evenly. The cause of this problem, though not clearly analyzed, is perhaps that the EKC cannot be completely removed from the surface of the underlying insulting film
12
and the remaining EKC has an adverse influence upon the growth rate of the Si0
2
film
15
.
In the case of
FIGS. 3A and 3B
, there has been the problem that, when the film is formed on the insulating film
22
, for example, a silicon thermal oxide film formed on the semiconductor substrate
21
by the thermal CVD method using a reaction gas including TEOS, the film forming rate is extremely slow on the insulating film
22
as compared with the case where the film is formed directly on the silicon substrate.
As the diameter of the wafer is enlarged from 200 mm to 300 mm, consumption of the chemicals is increased more and more. As a consequence, not only is the cost increased but also the drainage step takes an extreme amount of time, which creates environmental problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a substrate cleaning method capable of cleaning the interior of grooves having a narrow width and a deep depth, while reducing consumption of chemicals, and completely removing contaminants such as resist removing liquid, and forming a film on an insulating film with a desirable film forming rate.
In the present invention, a surface of a substrate is cleaned by use of a vapor including at least one of a vapor of sulfuric acid, a vapor of hydrochloric acid, a vapor of nitric acid and a vapor of chlorosulfonic acid (SO
2
Cl(OH)).
Since the chemicals are employed in vapor phase, consumption of the chemicals can be greatly reduced as compared to the case where a liquid is employed.
In addition, since a vapor of the chemicals is employed, the chemicals are in molecular form so that the chemical can enter into a groove with a narrow width and a deep depth. Accordingly, bottoms and side walls of grooves having an opening width of less than 0.3 &mgr;m and a deep depth can be completely cleaned.
Further, as has been experimentally demonstrated contaminants which are hard to remove, for example, resist removing liquids, on the insulating film are completely removed by using a liquid or vapor of chlorosulfonic acid.
As also confirmed experimentally, when an insulating film is formed on the underlying insulating film by the thermal CVD method, substantially the same growth rate as that in the case where the film is formed directly on the semiconductor substrate is achieved, especially when using a liquid or vapor of chlorosulfonic acid.
REFERENCES:
patent: 3775176 (1973-11-01), Cross et al.
patent: 5712198 (1998-01-01), Shive et al.
patent: 5952157 (1999-09-01), Kato et al.
patent: 2184311 (1990-07-01), None
patent: 5304126 (1993-11-01), None
patent: 7283192 (1995-10-01), None
patent: 11087291 (1999-03-01), None
JP 11-087291, Translation.
Kato Toshio
Tokumasu Noboru
Canon Sales Co., Inc.
Guerrero Maria
Jr. Carl Whitehead
Lorusso & Loud
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