Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1999-12-20
2002-09-17
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S459000, C438S048000
Reexamination Certificate
active
06452243
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a solid state image sensor and a method for fabricating the same, and more specifically to a solid state image sensor having a charge transfer electrode formed by patterning a single-layer conducting electrode material film.
In the prior art, this type of solid state image sensor includes a solid state image sensor having a photoelectric conversion section formed of a buried photodiode, as shown in
FIGS. 1A
to
1
D, which are diagrammatic sectional views for illustrating a process for fabricating the prior art solid state image sensor.
First, after a first P-type well
32
and second P-type wells
33
are formed on an N-type semiconductor substrate
31
by means of a thermal diffusion, phosphorus is ion-implanted to form a vertical charge transfer section
34
. Thereafter, boron is ion-implanted to form a channel stopper region
36
and an electric charge reading region
35
, as shown in FIG.
1
A.
A surface of the substrate
31
thus formed is thermally oxidized to form a gate oxide film
37
, and a charge transfer electrode material film
38
is deposited on the gate oxide film
37
by means of a low pressure CVD (chemical vapor deposition). Thereafter, a patterned photo resist layer
39
is formed for formation of a reading electrode, as shown in FIG.
1
B.
A dry etching is carried out by using the photo resist
39
as a masks to form a charge transfer electrode
40
. Phosphorus ions (P
+
) are ion-implanted in self-alignment manner using the charge transfer electrode
40
covered with the photo resist
39
, as a mask, so as to form an N-well
41
, which becomes a photodiode, as shown in FIG.
1
C. At this time, the photo resist
39
has a thickness of about 3 &mgr;m enough to prevent the phosphorus ions from passing through the photo resist
39
.
Thereafter, in order to form a buried photodiode, the photo resist
39
is removed, and then, boron ions (B
+
) are ion-implanted using the charge transfer electrode
40
as a mask, to form a P
+
region
42
, as shown in FIG.
1
D.
FIGS. 1A
to
1
D show the sectional views of the device in the course of fabricating the solid state image sensor. A layout pattern of the electrodes in a plan view becomes as shown in
FIG. 2. A
sectional view taken along the line B—B in
FIG. 2
corresponds to the sectional view of
FIGS. 1A
to
1
D. The layout pattern shown in
FIG. 2
is disclosed in Japanese Patent Application Pre-examination Publication No. JP-A-08-293592, (an English abstract of JP-A-08-293592 is available from the Japanese Patent Office and the content of the English abstract of JP-A-08-293592 is incorporated by reference in its entirety into this application).
The transfer electrode is constituted of a plurality of polysilicon layers (two layers in the example shown in FIG.
2
). The transfer electrode includes a first layer electric transfer electrode
52
and a second electric transfer electrode
53
in the form of a comb having each projection positioned on one vertical charge transfer section
51
, the first layer electric transfer electrode
52
and the second electric transfer electrode
53
being located to face to each other in a plan view in such a manner that each projection of the first layer electric transfer electrode
52
overlaps on a tip end of a corresponding projection of the second electric transfer electrode
53
.
Incidentally, the solid state image sensor shown in
FIG. 2
has such an arrangement that two electrodes are located adjacent to each other for each one photo electric conversion section
54
. In this construction, it is not possible to simultaneously read out a signal electric charge from all the photo electric conversion sections
54
.
In order to simultaneously read out the signal electric charge from all the one photo electric conversion sections
54
, it is necessary to arrange three electrodes adjacent to each other for each one photo electric conversion section
54
. For example, the arrangement as shown in
FIG. 3
is adopted. In the example shown in
FIG. 3
, the transfer electrode includes three layers of conducting electrode material film, namely, a first layer electric transfer electrode
62
, a second layer electric transfer electrode
63
and a third layer electric transfer electrode
64
. A sectional view taken along the line C—C in
FIG. 3
corresponds to the sectional view of
FIGS. 1A
to
1
D.
In the above mentioned prior art solid state image sensor, since the charge transfer electrode is constituted of a plurality of layers of conducting electrode material film, it is necessary to form a relatively thin interlayer film in order to ensure a sufficient insulation between the plurality of layers of electrode, with the result that a height of the device become high, and therefore, it becomes difficult to work. In addition, the step coverage of a light blocking or shielding film lowers, and a smear property is deteriorated.
In order to overcome the above mentioned problem, it may be considered to constitute the charge transfer electrode by a single-layer conducting electrode material film. In this case, in order to stabilize a reading characteristic for reading a signal charge from the photoelectric conversion section to the vertical charge transfer section, it is necessary to consider the plan pattern of the electrodes to form the photoelectric conversion section in self alignment to the vertical charge transfer electrode, so that when the ion-implantation is carried out for forming the photoelectric conversion section, an ion will never be implanted into a gap region between the electrodes.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a solid state image sensor and a method for fabricating the same, which have overcome the above mentioned problem of the prior art.
Another object of the present invention is to provide a solid state image sensor and a method for fabricating the same, capable of preventing a positional deviation between the photoelectric conversion section and the vertical charge transfer electrode, thereby to stabilize a reading characteristic for reading a signal charge from the photoelectric conversion section to the vertical charge transfer section.
The above and other objects of the present invention are achieved in accordance with the present invention by a solid state image sensor comprising a plurality of photoelectric conversion sections formed at a surface region of a first conductivity type semiconductor layer, a charge transfer section of a second conductivity opposite to that of the first conductivity type semiconductor layer, the charge transfer section being formed in the surface region of the first conductivity type semiconductor layer, adjacent to the photoelectric conversion sections, to transfer a signal charge along the charge transfer section, a plurality of charge reading sections each formed in the surface region of the first conductivity type semiconductor layer, between a corresponding one of the photoelectric conversion sections and the charge transfer section, for reading out a signal charge generated in the corresponding photoelectric conversion section, to the charge transfer section, and tranfer electrodes formed of a single layer of conducting electrode material to cover through a gate insulator film the charge reading sections and the charge transfer section, wherein the tranfer electrodes are formed by selectively etch-removing the single layer of conducting electrode material at a plurality of first regions which divide the single layer of conducting electrode material in a row direction for each one pixel, and at a second region positioned above each of the photoelectric conversion sections, the first regions and the second region being not overlapped to each other.
According to another aspect of the present invention, there is provided a method for fabricating a solid state image sensor which comprises a plurality of photoelectric conversion sections formed at a surface region of a first conductivity
Hatano Keisuke
Nakashiba Yasutaka
Dickstein , Shapiro, Morin & Oshinsky, LLP
Flynn Nathan
Wilson Scott R.
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