Solid state imaging device and method of manufacturing the same

Details Solid state imaging device and method of manufacturing the same Solid state imaging device and method of manufacturing the same

2000-10-06

2004-05-18

Glick, Edward J. (Department: 2882)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C348S322000

Reexamination Certificate

active

06737624

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a solid state imaging device and a method of manufacturing the same.
The solid state imaging device employed in the prior art will be explained with reference to
FIG. 14
to
FIG. 19
hereunder.
FIG. 14
is a plan view showing a solid state imaging device in the prior art. In
FIG. 14
,
101
denotes an n-type semiconductor substrate, and a p-well (not shown) made of p-type semiconductor layer is formed on a surface layer portion. Then, a plurality of photoelectric conversion devices
103
that are aligned at a predetermined distance in the column direction (vertical direction in
FIG. 14
) and the row direction (horizontal direction in
FIG. 14
) are formed on the p-well.
Charges accumulated in the photoelectric conversion devices
103
are read out to vertical charge transfer paths
105
after a predetermined time has elapsed. Then, a predetermined drive pulse is applied to vertical charge transfer electrodes (not shown) that are formed over the vertical charge transfer paths
105
, and thus the charges are transferred toward the downstream (toward lower side in
FIG. 14
) of the vertical charge transfer paths
105
. The vertical charge transfer paths
105
are formed by forming an n-type semiconductor layer on the p-well, and extend substantially in the column direction to pass through between the photoelectric conversion devices
103
.
The charges that are transferred in this manner reach eventually a horizontal charge transfer path
106
. The charges that reach the horizontal charge transfer path
106
comes up to an output circuit
107
by applying a predetermined drive pulse to a horizontal charge transfer electrode (not shown) that is formed over the horizontal charge transfer path
106
. The transferred charges are converted into a predetermined signal at the output circuit
107
and then output to the outside.
FIG. 15
is an enlarged view showing a pertinent portion of the solid state imaging device shown in
FIG. 14
in the prior art. In
FIG. 15
,
104
denotes a read gate portion. The charges accumulated in the photoelectric conversion devices
103
are transferred to the vertical charge transfer paths
105
through the read gate portion
104
by applying a field shift pulse to the vertical charge transfer electrodes (not shown) formed over the read gate portions
104
. Also,
102
denotes a device isolation region which is formed by doping high concentration impurity (B (boron)) into the surface layer portion of the p-well. The device isolation regions
102
extend substantially in the column direction to pass through between the photoelectric conversion devices
103
.
FIG. 16
is a view showing the solid state imaging device in the prior art to which the vertical charge transfer electrodes
108
that are omitted in
FIG. 15
are provided. As shown in
FIG. 16
, the vertical charge transfer electrode
108
has the well-known one pixel-two electrode structure. The interlace reading is performed by applying the well-known four phase drive pulse to the vertical charge transfer electrodes
108
.
FIG. 17
is a view showing an example of such four phase drive pulse. In
FIG. 17
, VH is a voltage applied when the charges accumulated in respective photoelectric conversion devices
103
are shifted to the vertical charge transfer paths
105
through the read gate portion
104
(when field shifting), and has a voltage of 15 V, for example. Also, VM and VL are voltages applied when the charges in the vertical charge transfer paths
105
are transferred to the downstream, and have a voltage of 0 V and −8 V respectively, for example.
In the solid state imaging device shown in
FIG. 15
in the prior art, the vertical charge transfer path
105
in a region A and a region B have following features. That is, in the region A, the device isolation region
102
is formed only on one side of the vertical charge transfer path
105
. In other words, only one side of the vertical charge transfer path
105
in the region A is defined by contacting to the device isolation region
102
.
In contrast, in the region B, the device isolation region
102
is formed on both sides of the vertical charge transfer path
105
. In other words, both sides of the vertical charge transfer path
105
in the region B are defined by contacting to the device isolation region
102
.
Therefore, an amount of the impurity (B (boron)) that diffuses from the device isolation region
102
into the vertical charge transfer path
105
in the region B is increased rather than that in the region A. The reason for this can be given as follows. That is, in the region A, since the device isolation region
102
is formed only on one side of the vertical charge transfer path
105
, diffusion of the impurity (B (boron)) occurs only from this device isolation region
102
formed on one side. On the contrary, in the region B, since the device isolation region
102
is formed on both sides of the vertical charge transfer path
105
, diffusion of the impurity (B (boron)) occurs from both sides of the vertical charge transfer path
105
. Accordingly, an amount of the impurity (B (boron)) that diffuses into the vertical charge transfer path
105
in the region B is increased rather than that in the region A.
In general, if the impurity is diffused into the vertical charge transfer path
105
, a height of potential of the vertical charge transfer path
105
is increased by the so-called narrow channel effect. Then, if an amount of diffused impurity is different between the region A and the region B, the height of potential of the vertical charge transfer path
105
in the region B becomes higher than that in the region A.
This point will be explained with reference to
FIGS. 18A and 18B
and
FIG. 19
hereunder.
FIG. 18A
is a view showing a sectional shape of the solid state imaging device in the prior art, taken along a C-D line in
FIG. 15
, and a schematic behavior of potential in the sectional shape.
FIG. 18B
is a view showing a sectional shape of the solid state imaging device in the prior art, taken along an E-F line in
FIG. 15
, and a schematic behavior of potential in the sectional shape. In
FIGS. 18A and 18B
, the vertical charge transfer electrodes
108
(
108
a
,
108
b
) that are omitted in
FIG. 15
are also shown. Also, as is evident from
FIG. 15
, a C-D sectional shape is one sectional shape in the region A, and an E-F sectional shape is one sectional shape in the region B.
Also, a curve indicated by a solid line in
FIGS. 18A and 18B
shows potential when the voltage applied to the vertical charge transfer electrodes (
108
a
,
108
b
) is at a low level (VL), while a curve indicated by a broken line shows potential when the applied voltage is at a middle level (VM).
As shown in
FIG. 18A
, in the C-D sectional shape in
FIG. 15
, when the voltage applied to the vertical charge transfer electrode
108
a
is at a low level (VL), a height of potential of the vertical charge transfer path
105
is HL
1
. Then, when the applied voltage is at a middle level (VM), the height of potential of the vertical charge transfer path
105
is HM
1
.
In contrast, as shown in
FIG. 18B
, in the E-F sectional shape in
FIG. 15
, when the voltage applied to the vertical charge transfer electrode
108
b
is at a low level (VL), a height of potential of the vertical charge transfer path
105
is HL
2
. Then, when the applied voltage is at a middle level (VM), the height of potential of the vertical charge transfer path
105
is HM
2
.
Because of the aforementioned difference in the amount of diffused impurity (B (boron)), HL
2
is higher than HL
1
(HL
2
>HL
1
), and HM
2
is higher than HM
1
(HM
2
>HM
1
).
FIG. 19
is a view showing a sectional shape of the solid state imaging device in the prior art, taken along a G-H line in
FIG. 16
, and a schematic behavior of potential in the sectional shape. A curve indicated by a solid line in
FIG. 19
shows behavior of potential in the G-H sectional shape when the voltage applied to the vertical charge transfer e

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