Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-05-19
2003-08-12
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S315000
Reexamination Certificate
active
06606124
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state imaging device and manufacturing method thereof, wherein the solid-state imaging device is provided with a plurality of photoelectric conversion portions so arranged that they form a matrix, i.e., two-dimensional pattern or array constructed of their rows and their columns, and more particularly to a solid-state imaging device and manufacturing method thereof, wherein the solid-state imaging device is adapted for use in image sensors of various types of image input instruments, for example such as facsimiles, video cameras, digital still cameras and like instruments.
2. Description of the Related Art
Solid-state imaging devices have long been constructed of charge coupled devices (i.e., CCDs), and provided with a plurality of photoelectric conversion portions, wherein each of the photoelectric conversion portions converts incident light into signal charge the amount of which charge corresponds to the amount of the incident light, and the photoelectric conversion portions are so arranged that they form a matrix, i.e., two-dimensional pattern or array constructed of their rows and their columns. Of these solid-state imaging devices, particularly, one having a construction in which the photoelectric conversion portion and the charge transfer portion for transferring the signal charge are separately formed is capable of performing separately each of the process of photoelectric conversion, process of charge readout and the process of charge transfer, and, therefore capable of being driven in various drive modes. Due to this, the solid-state imaging device is characterized by its very wide range of applications.
This type of the solid-state imaging device is known, for example, in a Japanese magazine: “Eizo Jyoho”, August issue for 1995, vol. 27, pp. 80-86. This solid-state imaging device is characterized in that: it doubles as a charge readout electrode for controlling the writing and the reading of the signal charge from the photoelectric conversion portion to the corresponding one of the charge transfer portions; and, the photoelectric conversion portion is formed by mask-alignment of the charge transfer electrode for controlling in transfer the signal charge of the corresponding one of the charge transfer portions.
Hereinbelow, a manufacturing method of the conventional solid-state imaging device disclosed in the above Japanese magazine (hereinafter referred to as the first conventional example) will be described in due order of manufacturing, i.e., process steps thereof with reference to FIGS.
33
(
a
) to
37
(
b
) First, as shown in FIG.
33
(
b
), a p-type well layer
2
is formed by ion-implanting a p-type impurity such as boron ions B
+
and like ions in an n-type semiconductor substrate
1
. Then, formed in a surface region of the p-type well layer
2
by ion-implanting a p-type impurity such as boron ions B
+
and like ions and an n-type impurity such as phosphorus ions P
+
and like ions are: a P
+
type channel stop
3
for isolating the devices from each other; a p-type charge readout portion
4
for retrieving the signal charge from the photoelectric conversion portion
6
(shown in FIG.
36
(
b
)) to an n-type charge transfer portion
5
; and, the n-type charge transfer portion
5
for transferring the signal charge thus retrieved. After that, as shown in FIG.
34
(
b
), a photoresist film
7
-is formed on the surface of the p-type well layer
2
other than an area in which the photoelectric conversion portion
6
will be formed later. Then, as shown in FIGS.
34
(
a
) and
34
(
b
), an n-type well
8
which will form the photoelectric conversion portion
6
later is formed by ion-implanting an n-type impurity such as phosphorus ions P
+
and like ions at an acceleration energy of more than or equal to 200 KeV using the photoresist film
7
as a mask. Subsequent to this, the photoresist film
7
is removed. Then, a gate insulation film
9
constructed of a thermal oxidation film, oxidation film, nitride film, oxide (ONO) film, or like film is formed over the entire surface of the substrate. Then, a gate electrode film (not shown) such as a polysilicon film and the like is formed over the gate insulation film
9
. Then, by removing an unnecessary region of the gate electrode film through a plasma etching process, a charge transfer electrode
10
is formed. Further formed on this charge transfer electrode
10
by using the thermal oxidation film and by a (CVD) chemical vapor deposition process is a CVD oxidation film which forms an interlayer insulation film (not shown). After forming the interlayer insulation film, as shown in FIGS.
35
(
a
) and
35
(
b
), a charge transfer electrode
11
which doubles as a charge readout electrode is formed over both the gate insulation film
9
and the interlayer insulation film.
As shown in FIGS.
36
(
a
) and
36
(
b
), the photoelectric conversion portion
6
is formed by self-alignment using the charge transfer electrodes
10
and
11
as masks in an ion implantation process of the p-type impurity such as boron ions B
+
and like ions in a shallow surface region of the n-type well layer
8
, and thereby forming a P
+
type region
12
for preventing dark current from occurring, which dark current occurs in the surface of the photoelectric conversion portion
6
to impair the SN (Signal-to-Noise) ratio at a time when the intensity of illumination is low. At this time, in order to prevent the above p-type impurity from being ion-implanted in the other region where charge detection portions and on-chip amplifiers and the like are formed, it is necessary to form a photoresist film over the other region described above. Then, an interlayer insulation film
13
is formed over the entire surface of the substrate. After that, as shown in FIGS.
37
(
a
) and
37
(
b
), a light shield film
14
made of tungsten, aluminum and like materials is formed over the interlayer insulation film
13
to prevent the same
13
from being exposed to light. Then, the light shield film
14
thus formed over the photoelectric conversion portion
6
is removed to form an opening portion
14
a
. Each of the n-type well layer
8
of the photoelectric conversion portion
6
and the p-type well layer
2
formed thereunder functions as a buried-type photodiode.
In the conventional solid-state imaging device produced by the manufacturing method described above, as shown in FIG.
35
(
b
), since the photoelectric conversion portion
6
is formed by mask-alignment using the edge portion
11
a
of the charge transfer electrode
11
as a mask, the conventional solid-state imaging device suffers from problems of large variations in readout voltage of the signal charge, which variations are caused by misalignment. Further, when a gap is produced between the photoelectric conversion portion
6
and the edge portion
11
a
of the charge transfer electrode
11
, the readout voltage remarkably increases. Consequently, in order to prevent the readout voltage from remarkably increasing, it is necessary to protrude the edge portion
11
a
by a distance of at least the corresponding amount of misalignment occurring in mask alignment, so that the edge portion
11
a
overlies the photoelectric conversion portion over the above distance. This reduces the opening portion
14
a
in area size, as shown in FIG.
37
(
b
). The opening portion
14
a
thus reduced in area size increases the tendency of the incident light to be reflected from the light shield film
14
.
In order to solve the above problem, Japanese Patent Laid-Open No. Hei5-6992 discloses another conventional solid-state imaging device in which a photoelectric conversion portion is formed by self-alignment using the edge portion of a charge transfer electrode as a mask.
Hereinbelow, a manufacturing method of the another conventional solid-state imaging device disclosed in the above document (hereinafter referred to as the second conventional example) will be described in due order o
Hatano Keisuke
Yamada Toru
Ho Tuan
NEC Electronics Corporation
Young & Thompson
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