Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
2001-07-11
2002-12-24
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S720000, C438S723000
Reexamination Certificate
active
06498103
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a solid-state imaging device.
BACKGROUND OF THE INVENTION
In recent years, it is common to provide solid-state imaging devices with chargecoupled devices (hereinafter “CCD” will be referred to) used for transferring charge. This solid-state imaging device has a configuration in which a plurality of light-receiving portions are arranged in a matrix, and a charge transfer portion is formed corresponding to each line of the matrix. The charge transfer portion is a CCD in which a transfer channel portion is formed in a silicon substrate and a transfer electrode is formed above the transfer channel portion via a gate insulating film. In such a solid-state imaging device, in order to improve the sensitivity by suppressing the reflection on the surface of the light-receiving portion, it has been proposed to form an anti-reflection film above the light-receiving portion.
FIGS. 5A
to
5
C are cross-sectional views to illustrate steps of a method for manufacturing a solid-state imaging device provided with an anti-reflection film. First, on the silicon substrate
50
provided with a light-receiving portion
52
and a transfer channel portion
51
, a silicon oxide film
53
, a silicon nitride film
54
and a silicon oxide film
55
are formed in this order, thereby forming a three-layered gate insulating film (see FIG.
5
A). Then, a polysilicon film is formed, followed by patterning thereof by photolithography and etching, thereby forming a transfer electrode
56
above the transfer channel portion
51
(FIG.
5
B). Next, the surface of the transfer electrode
56
is covered with a silicon oxide film
57
by thermal oxidization, followed by patterning of the silicon nitride film
54
, thereby forming an anti-reflecting film
54
a
above the light-receiving portion
52
(FIG.
5
C).
FIGS. 6A
to
6
E are cross-sectional views to illustrate steps of another method for manufacturing a conventional solid-state imaging device. Similar to
FIGS. 5A
to
5
B, on a silicon substrate
60
provided with a light-receiving portion
62
and a transfer channel portion
61
, a three-layered gate insulating film including a silicon oxide film
63
, a silicon nitride film
64
and a silicon oxide film
65
, and a transfer electrode
66
are formed (see FIG.
6
A and FIG.
6
B). Then, after a silicon oxide film
67
is formed on the surface of the transfer electrode
66
, the silicon nitride film
64
above the light-receiving portion
62
is removed (see FIG.
6
C). Thereafter, a new silicon nitride film
68
is formed (see FIG.
6
D), followed by patterning thereof so as to form an anti-reflecting film
68
a
above the light-receiving portion
62
(see FIG.
6
E).
FIGS. 6A
to
6
F are cross-sectional views to illustrate steps of another method for manufacturing a conventional solid-state imaging device. Similar to
FIGS. 5A
to
5
B, on a silicon substrate
60
provided with a light-receiving portion
62
and a transfer channel portion
61
, a three-layered gate insulating film including a silicon oxide film
63
, a silicon nitride film
64
and a silicon oxide film
65
, and a transfer electrode
66
are formed (see FIG.
6
A and FIG.
6
B). Then, after a silicon oxide film
67
is formed on the surface of the transfer electrode
66
, the silicon nitride film
64
above the light-receiving portion
62
is removed (see FIG.
6
C). Thereafter, a new silicon nitride film
68
is formed (see FIG.
6
D), followed by patterning thereof so as to form an anti-reflecting film
68
a
above the light-receiving portion
62
(see FIG.
6
E).
In general, as the etching for forming the transfer electrode, dry etching is carried out. However, in the manufacturing method shown in
FIGS. 5A
to
5
C, when the dry etching is carried out, not only the polysilicon film but also the silicon oxide film
55
and the silicon nitride film
54
above the light-receiving portion
52
are etched (see FIG.
5
B). As a result, the film thickness of the silicon nitride film, that is, the anti-reflection film
54
a
above the light-receiving portion
52
is reduced. Since the anti-reflecting effect is determined by the refractive index and film thickness of the anti-reflection film
54
a
, if the film thickness of the anti-reflection film
54
a
is reduced due to the dry etching, the anti-reflecting effect may be deteriorated.
On the other hand, in the manufacturing method shown in
FIGS. 6A
to
6
E, after dry etching for forming the transfer electrode, the silicon nitride film
64
above the light-receiving portion
62
is removed and then the new silicon nitride film is formed as an anti-reflection film (see
FIGS. 6C
to
6
E). Therefore, it is possible to avoid the reduction of the film thickness of the anti-reflection film and to achieve a sufficient anti-reflecting effect. However, since a step of removing the silicon nitride film
64
and a step of forming the new silicon nitride film
68
are required, the number of steps is increased, and the manufacturing efficiency is reduced.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is an object of the present invention to provide a method capable of efficiently manufacturing a solid-state imaging device provided with an anti-reflection film and capable of suppressing the film thickness of the anti-reflection film from being reduced due to the etching.
In order to achieve the above-mentioned objects, a method for manufacturing a solid-state imaging device includes: forming a transfer channel portion and a light-receiving portion in a silicon substrate; forming a silicon oxide film on the silicon substrate; forming a silicon nitride film on the silicon oxide film, the silicon nitride film acting as a gate insulating film together with the silicon oxide film above the transfer channel portion and acting as an anti-reflection film above the light-receiving portion; forming a protection film on the silicon nitride film; forming a polysilicon film above the silicon nitride film via the protection film at least above the light-receiving portion; and etching the polysilicon film so as to form a transfer electrode above the transfer channel portion; wherein the etching of the polysilicon film is carried out so that the polysilicon film is removed above the light-receiving portion while the protection portion remains above the light-receiving portion.
According to such a manufacturing method, since the silicon nitride film constituting the gate insulating film and the silicon nitride film constituting the anti-reflecting film are formed in the same step, a solid-state imaging device provided with an anti-reflection film can be manufactured efficiently. Furthermore, in the etching for forming a transfer electrode, above the light-receiving portion, since the protection film is present on the silicon nitride film, it is possible to suppress the reduction of the film thickness of the silicon nitride film (i.e., anti-reflection film). Therefore, it is possible to form the anti-reflection film having a film thickness serving the anti-reflecting purpose, and to manufacture a solid-state imaging device that is excellent in sensitivity.
In the above-mentioned manufacturing method, it is preferable that the film thickness of the protection film is in the range from 5 nm to 100 nm at least above the light-receiving portion. It is preferable because it is possible to sufficiently suppress the reduction of the film thickness of the anti-reflection film due to the etching for forming the transfer electrode.
Furthermore, in the above-mentioned manufacturing method, it is preferable that the film thickness of the silicon nitride film is in the range from 5 nm to 100 nm at least above the light-receiving portion. It is preferable because a further excellent anti-reflecting effect can be achieved.
Furthermore, in the above-mentioned manufacturing method, it is preferable that the protection film is thinned or removed at least above the transfer channel portion before the polysilicon film is formed. It is preferabl
Kuriyama Toshihiro
Nishio Rieko
Senda Hiroyuki
Yamaguchi Takumi
Chen Kin-Chan
Utech Benjamin L.
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