Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2003-01-31
2004-12-21
Munson, Gene M. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S222000, C257S233000
Reexamination Certificate
active
06833601
ABSTRACT:
This application claims priority to Japanese Patent Application Number JP2002-028585 filed Feb. 5, 2002, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a semiconductor device suitably used for a photoelectric transducer such as a photocoupler or the like, a solid-state imaging device or field-effect imaging device comprising a semiconductor image sensor which receives light incident on an on-chip lens formed on a color filter, a method of manufacturing the semiconductor device, and an apparatus for manufacturing a semiconductor.
More specifically, a refractive index matching film is provided on a photoelectric conversion light-receiving element, and a composition composed of silicon, oxygen and nitrogen which constitute the refractive index matching film is adjusted so that the refractive index of a compound layer constituting the refractive index matching film continuously changes from the refractive index of a silicon oxide film of 1.45 to the refractive index of a silicon nitride film of 2.0. As a result, reflection from the light receiving element can be minimized, and light receiving sensitivity can be improved.
2. Description of the Related Art
In recent years, a video camera and a digital still camera have been increasingly used in many schools, homes and broadcast stations. Such a camera requires a solid-state imaging device. The solid-state imaging device comprises CCD (Charge Coupled Device) imaging devices arranged as photoelectric transducers in a two-dimensional form. The CCD imaging device means a semiconductor device having a structure in which unit elements each comprising a photodiode and a MOS capacitor are regularly arranged. The solid-state imaging device has the function to move a group of charges stored in the surface of a semiconductor substrate along the array direction of electrodes of the MOS capacitors.
Namely, the solid-state imaging device comprises pluralities of photodiodes, MOS capacitors, vertical transfer registers, horizontal transfer registers, and charge detecting amplifiers, which are provided on the semiconductor substrate. When light is applied to a light receiving surface of the solid-state imaging device, the light is converted into signal charges by the photodiodes, and then stored in the MOS capacitors. The signal charges stored in the MOS capacitors are transferred by the vertical transfer registers (referred to as “vertical CCD sections” hereinafter) and horizontal transfer registers, and finally detected by the charge detecting amplifiers and read as analogue received signals.
FIG. 14
is a sectional view showing an example of a configuration of a solid-state imaging device
10
of a first conventional example. As shown in
FIG. 14
, a semiconductor buried layer (P-WELL)
1
is formed on a N-type silicon substrate
11
, the P-WELL
1
comprising photodiodes PD each having a N-type impurity region (impurity diffused layer)
2
, and vertical CCD sections
12
each having a N-type impurity region (impurity diffused layer)
3
. The P-WELL
1
further comprises transfer gate sections
13
for reading out signal charges from the photodiodes PD to the vertical CCD sections
12
, to isolate the silicon substrate
11
.
The N-type impurity region
2
constituting each of the photodiodes PD is isolated from the N-type impurity region
3
constituting the corresponding vertical CCD section
12
by a channel stopper
4
comprising a P-type impurity region. Furthermore, a transfer electrode
17
is provided on each of the vertical CCD sections
12
through a gate insulating film (silicon oxide film)
14
.
The transfer electrodes
17
of the vertical CCD sections
12
are covered with a shielding film
19
composed of aluminum or tungsten through an interlayer insulating film
18
. The shielding film
19
has apertures formed above the photodiodes PD to define light-receiving windows
21
. The shielding film
19
is coated with a cover film
22
comprising a silicon oxide film of PSG or the like. Furthermore, a planarizing film
23
, a color filter
24
, and microlenses
25
are formed in order on the cover film
22
.
The material of the cover film
22
is not limited to the silicon oxide film, and an example using a silicon nitride film is also known. For example, the technical document, Japanese Unexamined Patent Application Publication No. 60-177778, discloses that a plasma silicon nitride film is formed on a transparent electrode composed of polycrystalline silicon. However, in such a structure in which a silicon nitride film is deposited, an increase in short-wavelength sensitivity is expected due to a multiple interference effect.
Therefore, in the structure shown in
FIG. 14
in which the silicon interfaces of the photodiodes PD are covered directly with the cover film
22
, a loss of incident light is increased due to surface reflection from the N-type silicon substrate
11
to fail to obtain sufficient light receiving sensitivity.
In addition, in the structure in which the plasma silicon nitride film is formed below the planarizing film
23
, ripple occurs in spectral transmittance due to an interference effect between a silicon nitride film serving as the interlayer insulating film
18
and a silicon nitride film serving as the gate insulating film
14
provided below the interlayer insulating film
18
. Therefore, the spectral characteristics of the color filter layer
24
easily vary.
In order to solve the above-described problem, for example, Patent Publication No. 3196727 discloses a technique for forming an anti-reflection film on photodiodes PD.
FIG. 15
is a sectional view showing an example of a construction of a solid-state imaging device
10
′ of a second conventional example.
The solid-state imaging device
10
′ shown in
FIG. 15
comprises a N-type silicon substrate
11
on a surface of which photodiodes PD are formed for obtaining signal charges. Each of the photodiodes PD comprises a N-type impurity region (impurity diffused region)
2
.
Furthermore, a silicon oxide thin film serving as a gate insulating film
14
is formed on the silicon substrate
11
, and a silicon nitride film serving as an anti-reflection thin film
15
having a refractive index higher than that of the silicon oxide film
14
and lower than that of the silicon substrate
11
is formed on the silicon oxide thin film
14
. The refractive index of the silicon oxide film
14
is about 1.45, and the refractive index of the silicon nitride film is about 2.0. Assuming that the refractive index is n, the thickness t of each of the silicon oxide film and the silicon nitride film is set to satisfy the relationship 350/(4n) nm≦t≦450/(4n) nm. These films
14
and
15
are formed for preventing a dark current.
When the thickness of each of the silicon oxide film and the silicon nitride film is set as described above, the anti-reflection film
15
having relatively flat reflection in the visible light region can be obtained. By appropriately setting the thickness of each of the silicon oxide film and the silicon nitride film, reflectance can be suppressed to an average of about 12 to 13%, and is thus suppressed to about ⅓ of the reflectance of the conventional silicon substrate
11
of about 40%.
Like in the first conventional example, transfer electrodes
17
are formed on the vertical CCD sections
12
through a silicon oxide film. Furthermore, a shielding film
19
composed of aluminum or tungsten is deposited through an interlayer insulating film
18
, the shielding film
19
having apertures respectively formed above the photodiodes PD.
A cover film
22
is formed on the shielding film
19
. The cover film
22
comprises a PSG film serving as a silicon-based passivation film, and has a refractive index of about 1.46. In addition, a planarizing layer
23
, a filter layer
24
, and microlenses
25
are formed on the cover film
22
. The refractive index of the color filter layer
24
is about 1.5 to 1.6, and is thus substantially the same as the passivatio
Depke Robert J.
Holland & Knight LLP
Munson Gene M.
Sony Corporation
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