Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2000-09-20
2002-04-30
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S072000
Reexamination Certificate
active
06379993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state imaging device and a method of manufacturing such a solid-state imaging device, and more particularly to a solid-state imaging device having a film disposed on a sensor thereof for suppressing light reflections from a semiconductor substrate, and a method of manufacturing such a solid-state imaging device.
2. Description of the Related Art
Conventional solid-state imaging devices are disclosed in Japanese Patent Laid-Open Publication No. 206571/92 and Japanese Patent Laid-Open Publication No. 152674/92, for example. The disclosed solid-state imaging devices have a reflection-resistant film disposed on the entrance surface of a photodiode for increased sensitivity thereof.
The solid-state imaging device disclosed in Japanese Patent Laid-Open Publication No. 206571/92 is shown in
FIG. 1
of the accompanying drawings. As shown in
FIG. 1
, the solid-state imaging device has a photodiode
55
as a sensor and a vertical CCD (Charge-Coupled Device)
56
which are disposed in a surface layer of a silicon substrate
59
. A silicon oxide film
49
serving as an oxide film is disposed over the photodiode
55
and the vertical CCD
56
. An intermediate-refractive-index film
48
is disposed on the surface of the silicon oxide film
49
. The silicon oxide film
49
and the intermediate-refractive-index film
48
are shared by the photodiode
55
and the vertical CCD
56
.
Gate electrodes
46
are disposed on the surface of the intermediate-refractive-index film
48
over the vertical CCD
56
. The gate electrodes
46
are covered with light blocking films
44
of aluminum (Al) or tungsten (W) with interlayer insulating films
45
interposed therebetween. The surfaces of the light blocking films
44
and the surface of the intermediate-refractive-index film
48
over the photodiode
55
are covered with a protective film
43
such as a silicon oxide film. The intermediate-refractive-index film
48
comprises a silicon nitride film. The silicon nitride film as the intermediate-refractive-index film
48
has a refractive index which is of a substantially intermediate value between the refractive index of the silicon oxide film as the protective film
43
and the refractive index of the silicon substrate
59
. The refractive index of the intermediate-refractive-index film
48
is smaller than the refractive index of the silicon substrate
59
, and the refractive index of the protective film
43
is smaller than the refractive index of the intermediate-refractive-index film
48
. A planarizing film
42
is disposed on the surface of the protective film
43
for planarizing surface irregularities of the protective film
43
.
FIG. 2
of the accompanying drawings shows the solid-state imaging device disclosed in Japanese Patent Laid-Open Publication No. 152674/92. As shown in
FIG. 2
, the solid-state imaging device has a photodiode
75
and a vertical CCD
76
which are disposed in a surface layer of a silicon substrate
79
that is covered with a gate film
70
. Gate electrodes
66
are disposed on the gate film
70
over the vertical CCD
76
. An intermediate-refractive-index film
68
is disposed over surfaces and sides of ends of the gate electrodes
66
and the surface of the photodiode
75
with an insulating film interposed therebetween.
Light blocking films
64
are disposed over the surfaces of the gate electrodes
66
and the surfaces of the intermediate-refractive-index film
68
superposed on the ends of the gate electrodes
66
with an interlayer insulating film
65
interposed therebetween. The surfaces of the light blocking films
64
and the surface of the interlayer insulating film
65
over the photodiode
75
are covered with a protective film
63
. The intermediate-refractive-index film
68
has a refractive index which is of a substantially intermediate value between the refractive index of a silicon oxide film used as the interlayer insulating film
65
and the protective film
63
and the refractive index of the silicon substrate
79
. The refractive index of the intermediate-refractive-index film
68
is smaller than the refractive index of the silicon substrate
79
, and the refractive index of the interlayer insulating film
65
and the protective film
63
is smaller than the refractive index of the intermediate-refractive-index film
68
.
In the solid-state imaging device shown in
FIG. 2
, the ends of the intermediate-refractive-index film
68
overlap the ends of the gate electrodes
66
. The thickness of the film between the sides of the ends of the gate electrodes
66
and the intermediate-refractive-index film
68
is greater than the thickness of the film between the intermediate-refractive-index film
68
and the photodiode
75
. These dimensional features are effective to reduce any smearing of image signals generated by the solid-state imaging device.
In both the conventional solid-state imaging devices shown in
FIGS. 1 and 2
, the silicon substrate having the photodiode and a thin film such as the silicon oxide film on the photodiode have largely different refractive indices. In order to minimize light reflections from a boundary surface between the silicon substrate and the thin film, the intermediate-refractive-index film is used as a reflection-resistant film. As described above, the refractive index of the intermediate-refractive-index film is of a substantially intermediate value between the refractive index of the thin film such as the silicon oxide film on the silicon substrate and the refractive index of the silicon substrate. The intermediate-refractive-index film which is disposed on the surface of the silicon substrate either directly or with the insulating film interposed therebetween is effective to suppress light reflections from the semiconductor substrate. As a result, the sensitivity of the solid-state imaging device is increased.
With the solid-state imaging device disclosed in Japanese Patent Laid-Open Publication No. 206571/92, the intermediate-refractive-index film which covers the entire surface of the semiconductor substrate comprises a silicon nitride film which has a low hydrogen permeability. The intermediate-refractive-index film of a low hydrogen permeability which covers the entire surface of the semiconductor substrate fails to provide a hydrogen alloying effect. Hydrogen alloying occurs to reduce oxygen in the semiconductor substrate with hydrogen and remove the reduced oxygen from the semiconductor substrate. Upon hydrogen alloying, hydrogen passes through the silicon oxide film and tungsten. However, since hydrogen is blocked by the silicon nitride film as the intermediate-refractive-index film and does not reach the semiconductor substrate, no hydrogen alloying effect takes place. As a result, the solid-state imaging device produces an increased dark current.
The solid-state imaging device disclosed in- Japanese Patent Laid-Open Publication No. 152674/92 has intermediate-refractive-index films associated with respective photodiodes. In the fabrication of the disclosed solid-state imaging device, it is necessary to deposit an intermediate-refractive-index film over the entire surface of the semiconductor substrate and thereafter etch away unwanted areas of the deposited intermediate-refractive-index film. Consequently, the process of fabricating the disclosed solid-state imaging device needs an additional step of etching away unwanted areas of the deposited intermediate-refractive-index film.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a solid-state imaging device including an intermediate-refractive-index film disposed over a photodiode, which solid-state imaging device is of high sensitivity and can be fabricated without impairing a hydrogen alloying effect.
Another object of the present invention is to provide a method of manufacturing a solid-state imaging device of high sensitivity according to a relatively simple fabrication process without impairing a hydrogen alloying effect.
To achi
Arai Kohichi
Mutoh Nobuhiko
Nakano Takashi
Teranishi Nobukazu
Chaudhari Chandra
Hayes & Soloway P.C.
NEC Corporation
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