Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
1999-12-06
2004-08-31
Lohe, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S223000, C257S225000, C257S229000, C257S232000, C257S233000, C438S048000, C438S060000, C438S073000, C438S075000, C348S294000, C348S311000, C348S315000
Reexamination Certificate
active
06784469
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state image pickup device suitable for a CCD solid-state image pickup device, typically, of a total pixel readout type, and a fabrication method thereof.
FIG. 17
shows an essential portion of an image pickup region of a conventional total pixel readout type CCD solid-state image pickup device. A CCD solid-state image pickup device
1
shown in
FIG. 17
, if being of an inter line transfer (IT) type, includes an image pickup region
4
and a horizontal transfer register having a CCD structure (not shown). The image pickup region
4
includes a plurality of light receiving portions
2
for photoelectric conversion, which portions are taken as pixels arranged in a matrix, and a plurality of vertical transfer registers
3
each of which has a CCD structure and which is formed on one side of each column of the light receiving portions
2
. The horizontal transfer register is used for transferring signal charges transferred from the vertical transfer registers
3
to an output unit.
FIG. 18A
is a sectional view taken on line A
1
—A
1
of
FIG. 17
, and
FIG. 18B
is a sectional view taken on line B
1
—B
1
of FIG.
17
. Referring to
FIGS. 18A and 18B
, the vertical transfer register
3
has transfer electrodes having a three-layer structure formed on a transfer channel region of a silicon semiconductor base
6
via a gate insulating film
7
. These transfer electrodes are composed of first transfer electrodes
8
A formed by a first polysilicon layer, second transfer electrodes
8
B formed by a second polysilicon layer, and third transfer electrodes
8
C formed by a third polysilicon layer, which are repeatedly arranged along a charge transfer direction “a”. Reference numeral
9
designates an interlayer insulating film. Each of the first transfer electrodes
8
A is formed into a band-shape extending in the horizontal direction in such a manner as to be common to a plurality of columns of the vertical transfer registers
3
. The same is true for the second and third transfer electrodes
8
B and
8
c.
In the region between the light receiving portions
2
adjacent to each other in the vertical direction, the first, second, and third transfer electrodes
8
A,
8
B and
8
C are sequentially stacked.
The solid-state image pickup device
1
is configured such that the transfer electrode
8
of the vertical transfer register
3
is divided into the three parts, that is, the first, second and third transfer electrodes
8
A,
8
B and
8
C for each pixel (light receiving portion
2
), and is three-phase driven for total pixel readout by applying three-phase vertical drive pulses øV
1
, øV
2
, and øV
3
shown in
FIG. 19
to these transfer electrodes
8
A,
8
B and
8
C, respectively.
Another CCD solid-state image pickup device
11
having a configuration shown in
FIG. 15
has been proposed. The device
11
is four-phase driven for total pixel readout by applying four-phase vertical drive pulses to transfer electrodes having a three-layer structure of each vertical transfer register.
FIG. 16A
is a sectional view taken on line A
2
—A
2
of FIG.
15
. Referring to
FIGS. 15 and 16A
, the CCD solid-state image pickup device
11
is configured such that transfer electrodes
8
of a vertical transfer register
3
are formed by three polysilicon layers. To be more specific, second and fourth transfer electrodes
8
B and
8
D formed by the second polysilicon layer are alternately arranged along a charge transfer direction; each first transfer electrode
8
A formed by the first polysilicon layer is disposed between the second and fourth transfer electrodes
8
B and
8
D arranged in this order, for example, from the left side in
FIG. 16A
; and each third transfer electrode
8
C formed by the third polysilicon layer is disposed between the fourth and second transfer electrodes
8
D and
8
B arranged in this order, for example, from the left side in FIG.
16
A.
FIG. 16B
is a sectional view taken on line B
2
—B
2
of FIG.
15
. Referring to
FIG. 16B
, in the region between the light receiving portions
2
adjacent to each other in the vertical direction, the second and fourth transfer electrodes
8
B and
8
D formed by the second layer are stacked on the first transfer electrode
8
A formed by the first layer, and the third transfer electrode
8
C formed by the third layer is stacked on the second and fourth electrodes
8
B and
8
D.
The solid-state image pickup device
11
is configured such that the transfer electrode
8
of the vertical transfer register
3
is divided into the four parts, that is, the first, second, third, and fourth transfer electrodes
8
A,
8
B,
8
C and
8
D for each pixel (light receiving portion
2
), and is four-phase driven for total pixel readout by applying four-phase vertical drive pulses øV
1
, øV
2
, øV
3
, and øV
4
, shown in
FIG. 3
to these transfer electrodes
8
A to
8
D, respectively.
The other configuration is the same as that shown in FIG.
17
and
FIGS. 18A and 18B
, and therefore, corresponding parts are designated by the same characters and the overlapped explanation is omitted.
In the CCD solid-state image pickup device
1
shown in
FIG. 17
, since the vertical transfer register
3
is three-phase driven by the transfer electrode
8
divided into the three parts, that is, the first, second and third transfer electrodes
8
A,
8
B and
8
C, the accumulated charge capacity in the vertical transfer register
3
is equivalent to one-third of the accumulated charge capacity in the vertical transfer path for one pixel. As a result, to ensure a sufficient accumulated charge capacity in the transfer portion, the width W
1
of the transfer path must be broadened; however, if the width W
1
of the transfer path is broadened, the area of the light receiving portion
2
is reduced in proportional to the broadened width W
1
.
The areas of the three transfer electrodes
8
A to
8
C divided from the transfer electrode
8
for each pixel may be desirable to be equalized to each other for ensuring a larger accumulated charge capacity; however, they actually become uneven largely depending on variations in processed line width among the transfer electrodes
8
A to
8
C. As a result, the accumulated charge capacity is determined by one of the transfer electrodes
8
A to
8
C having the smallest area, to thereby reduce the actual charge amount.
In the CCD solid-state image pickup device
11
shown in
FIG. 15
, which is four-phase driven for total pixel readout by the three-layer electrode structure, since the accumulated charge capacity is equivalent to two-fourth of the accumulated charge capacity in the vertical transfer path for one pixel, it becomes larger than that in the CCD solid-state image pickup device
1
shown in
FIG. 17
, which is three-phase driven for total pixel readout by the three-layer electrode structure.
The CCD solid-state image pickup device
11
, however, has the following disadvantage: namely, a variation in line width occurs between the transfer electrode
8
A formed by the first layer and each of the transfer electrodes
8
B and
8
D formed by the second layer and also a misalignment occurs between the transfer electrode
8
A formed by the first layer and each of the transfer electrodes
8
B and
8
D formed by the second layer, so that variations occur among lengths L
1
, L
2
, L
3
and L
4
of the two-phase transfer regions each of which is composed of the adjacent transfer electrodes for two-phases and is taken as a factor determining the accumulated charge capacity, to thereby reduce the actual charge amount.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solid-state image pickup device intended to increase the accumulated charge capacity, increase the area of a light receiving portion, and prevent a reduction in actual charge amount due to variations in processed dimension between transfer electrodes, and a method of fabricating the solid-state image pickup device.
To achieve the above object, according to a first aspect of the present in
Hikichi Kunihiko
Yamane Junji
Kang Donghee
Lohe Steven
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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