Solid-state image pickup device

Details Solid-state image pickup device Solid-state image pickup device

2000-08-17

2004-10-19

Ho, Tuan (Department: 2615)

Television

Camera, system and detail

Solid-state image sensor

C257S232000

Reexamination Certificate

active

06806904

ABSTRACT:

This application is based on Japanese Patent Application HEI 11-231998 filed on Aug. 18, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a solid-state image pickup device, and in particular, to a structure of a vertical charge transfer path of a solid-state image pickup device.
b) Description of the Related Art
FIG. 9
generally shows a solid-state image pickup device in a plan view.
The configuration of
FIG. 9
includes a solid-state image pickup device
100
including a semiconductor substrate
101
and a large number of pixels
103
arranged in a matrix (i.e., in rows and columns). Each pixel
103
includes a photodiode (a photoelectric converter or transducer element)
103
a
, a readout gate or a transfer gate
103
b.
For each column of pixels, a vertical charge transfer path
105
is formed. Each path
105
includes a layer of a semiconductor of first conductivity type (n-type). The readout gate
103
b
is disposed between each photodiode
103
a
and the first-conductivity-type semiconductor layer. The first-conductivity-type (n-type) semiconductor layer is used as a charge transfer channel. The configuration further includes a horizontal charge transfer path
107
and an amplifier
111
.
Each vertical charge transfer path
105
includes an end electrically connected to the horizontal charge transfer path
107
. The horizontal path
107
includes an end connected to the amplifier
111
.
The photodiode
103
a
generates an electric signal (electric charge) through photoelectric conversion. The signal or charge is transferred via the readout gate
103
b
to the vertical charge transfer path
105
. The charge is vertically transferred through the path
105
, for example, by four-phase driving and is delivered to the horizontal charge transfer path
107
. In the path
107
, the charge is transferred to the amplifier
111
, for example, by two-phase driving. The amplifier
111
amplifies the electric signal thus transferred and outputs information of an image to an external device.
The solid-state image pickup device
100
includes a field area or zone
117
other than the areas in which the constituent components such as the photodiodes
103
a
, the readout gates
103
b
, the vertical charge transfer paths
105
, the horizontal charge transfer paths
107
, and the output amplifier
111
are disposed.
In this structure, it is desirable to prevent surmounting of electrons over, for example, areas (1) to (3), listed below, in the field area
117
. This is because the surmounting of electrons possibly causes an erroneous operation in the image pickup device
100
.
(1) An area other than the readout gate
103
b
in an area between the photodiode
103
a
and the associated vertical charge transfer path
105
(first areas
121
a
and
121
b
of FIG.
9
).
(2) An area between the vertical charge transfer path
105
and the photodiode
103
a
which is not connected by the readout gate
103
b
to the path
105
and which is horizontally next to the path
105
(a second are 125 of FIG.
9
).
(3) An area between vertically adjacent photodiodes
103
a
among the photodiodes
103
a
connected via the readout gate
103
b
to the vertical charge transfer path
105
(a third area
131
of FIG.
9
).
To prevent the erroneous operation above, there is formed, in a periphery of the first-conductivity-type (n-type) semiconductor layer of each vertical charge transfer path
105
in a plan view, an isolation area rib or zone such as a channel stop area in other than the areas in which the readout gates
103
b
are arranged. Similarly, between the photodiodes
103
a
sequentially arranged in a direction of the pixel column, an isolation area such as a channel stop area is disposed.
When the image pickup devices
100
has a pixel density not exceeding a particularly large value, distance between the photodiodes
103
a
in the first to third areas
121
,
125
, and
131
or distance between the photodiodes
103
a
and the vertical charge transfer path
105
therein can be set to a fully great value. Namely, the isolation areas having a sufficient width can be manufactured in these areas
121
,
125
, and
131
. Consequently, there exists little fear of the erroneous operation above.
However, with increase in the pixel density of solid-state image pickup devices in recent years, it is difficult to take such satisfactorily long distance, for example, between the photodiodes
103
a
or between the photodiodes
103
a
and the vertical charge transfer path
105
in the first to third areas
121
,
125
, and
131
. The isolation area cannot have sufficient width in the areas
121
,
125
, and
131
.
In a case in which the isolation area is formed by a channel stop area, the electric isolation can be desirably obtained by increasing an impurity concentration of the channel stop area even if width thereof is reduced to a relatively narrow value.
However, when the impurity concentration is increased in the channel stop area, narrow channel effect easily occurs in a place where the channel stop area is disposed on both sides in a direction of width of the first-conductivity-type (n-type) semiconductor layer of the vertical charge transfer path. The narrow channel effect then locally changes a transfer efficiency and a saturation output of charge in the vertical charge transfer path. It is therefore difficult to transfer charge to the horizontal charge transfer path in a stable state.
Particularly, the narrow channel effect easily appears in a solid-state image pickup device including a shifted-pixel layout, which no expected as a structure to cope with high pixel density.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a solid-state image pickup device capable of solving the problem associated with increase in the pixel density.
According to one aspect of the present invention, there is provided a solid-state image pickup device, comprising: a semiconductor substrate having a two-dimensional surface; a large number of photoelectric converter elements including a semiconductor region of first conductivity type, said photoelectric converter elements being arranged on the surface of said semiconductor substrate in a plurality of columns with a fixed pitch and a plurality of rows with a fixed pitch, said photoelectric converter elements in each odd column being shifted about one half of the pitch in each said column relative to said photoelectric converter elements in each even column, said photoelectric converter elements in each odd row being shifted about one half of the pitch in each said row relative to said photoelectric converter elements in each even row, each said photoelectric converter element column including said photoelectric converter elements of only said odd rows or said even rows; a plurality of isolation areas each formed on the surface of said semiconductor substrate between each pair of adjacent ones of said photoelectric converter element columns, each said isolation area including a semiconductor layer of second conductivity type generally extending in a direction of said photoelectric converter element column, while locally meandering; and a plurality of vertical charge transfer paths each formed between each said photoelectric converter element column and adjacent one of said isolation areas on one side of said photoelectric converter element column in a direction of said photoelectric converter element row, each said vertical charge transfer path including a semiconductor layer of first conductivity type generally extending in said photoelectric converter element column direction, while locally meandering, said vertical charge transfer path having width W
1
between each said photoelectric converter element of said column and said adjacent isolation area and width W
2
between said photoelectric converter elements adjacent to each other in said column, said width W
2
being larger than said width W
1
.
According to another aspect of the p

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