Note: Descriptions are shown in the official language in which they were submitted.
i07~06
BAGKGROUND OF THE INVENTION
Field of the Invention: . . ..
The present invention relates generally to a solid state
image sensing device, and is directed more particularly to a solid
state image sensor device of a frame transfer system which employs a
charge transfer device (which will be referred hereinafter to as a
CT D).
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram showing a pnor ;art
solid state image sensor device;
Figure 2 is a fragmentary top p1an diagram, showing in
enlarged scale, an image sensing array used in a prior art solid state
image sensor device shown in Figure l;
Figure 3 is a cross-sectional view taken on the line A-A
in Figure 2;
Figure 4 is a cross-sectional view of another pr or art
image sensing array;
Figure 5 is a fragmentary tOp plan view showing in
enlarged scale the main part of an image sensing array of a solid state
image sensor device according to the invention;
Figures 6, 7 and 8 are cross- sectional views taken on
the lines A-A, B-B and C-C in Figure 5, respectively;
Figures 9A to 9H, inclusive, are cross-sectional views
used for explaining the process for making the solid sta.te image
sensor device of the invention;
Figures 10A and l0B are voltage waveform diagrams used
for the explanation of the operation of the invention;
q~
1V7~806
Figure 11 is a fragmentary top plan view showing another
example of the invention; and
Figure 12 is a cross-sectional view taken on the line D-D
in Figure I 1.
Description of the Prior Art:
.
A prior art solid state image sensing device of the frame
transfer system will be described with reference to Figure 1. This
prior art image senso~ device consists of an image sensing array 1
which will produce an electric charge or carrier pattern corresponding
to picked-up pattern or amount of received light, a temporary storage
array 2 which temporarily stores the charge pattern from the image
sensing array 1, and a shift register 3 which sequentially transfers the
signals from the storage array 2 to an ou~put terminal t. The image
sensing array lis formed of a plurality of CIDs 4 aligned in the
vertical direction, the temporary storage array 2 is formed of a
plurality ~ CCDs 4 aligned in correspondence with the arrays 4 of the
image sensing array 1, and the shift register 3 is forrned also of the
CCD 4. In order to produce an electric charge or carrier pattern
corresponding to a light image to be received on the image sensing
ar:ay 1, image sensing cells are formed in the image sensing array 1.
An example of the image sens'ing array 1 will be now
described with reference to Figures 2 and 3. A semiconductor substrate,
for example, a silicon substrate 5, which is of low impurity concen-
tration, has provided on its one major surface an insulating layer 6
made of silicon dioxide SiO2 or the like. On the insulating layer 6
there are forrned s~rip electrodes 7 which are arranged common to the
respective CIDs 4, and extended in the horizontal direction with a gap
G be~ween adjacent ones. ~very third electrode 7 is connected together
and the electrodes 7 connected together are supplied with 3-phase clock
1(~70~ 6
pulses 01~ ~2 and 03, respectively. Between adjacent CTDs 4 there is
forrned a strip channel stopper region 8 of high impurity concentration
which faces the major surface of the semiconductor substrate 5.
An image sensing cell 9 is formed in the gap G belween
the adj acent electrodes 7 and between the adj acent channe~l stoppers 8.
Electric charges or carriers produced on the image sensing cells 9
in résponse to the amount of received lights are t~r~;nsferred successively
in, for example, the column direction by the cloc~`pulses 01~ ~2 and
03, and then transferred to the temporary SIOrage array 2.
With Ihe prior art solid state image sensing device con-
structed as above, since the image sensing cell 9 is formed between
the adjacent transfer electrodes 7, it is desired so as to increase its
Ught receiving efficiency that the width of the gap G is selected large.
However, if this width of the gap G is made large, a disadvantage
results from the fact that the carrier transfer efficiency is lowered;
that is, the light receiving efficiency is contradictory tO the carrier
transfer efficiency.
Figure 4 shows another example of the CID 4 which forms
the image sensing cell 9. ln the example of Figure 4, an-impurity is
selectively doped at high concentration to the insulating layer 6 formed
on the semiconductor substrate 5 tO form first strip transfer electrodes
7A, which are made of a polycrystalline silicon layer of low resistivity
and which are arranged with a predetermined gap between adjacent
ones. Then, a second insulating layer 6' made of SiO2 is coated so as
to cover all of the strip electrodes 7A and the insulating layer 6
between the adjacent electrodes 7A, and a second strip transfer
electrode 7B made of, for example, aluminum is formed on the portion
between the first electrodes 7A on which the insulating layers 6 and 6'
--3--
1~)7~306
are formed. The first and second electrodes 7A and 7B are electrically
connected at their one ends to form the transfer electrode 7. The
every second transfer electrodlo 7 is connected commonly to provide
two sets of electrodes. The two sets of electrodes 7 are supplied with
the clock pulses 01 and 02 to transfer the carriers. Such a type of
CID is called a 2-phase CrD In such a type of CrD, the image
sensing cell 9 is formed between the adjacent second electrodes 7B of
the transfer electrodes 7 and receives light along arrows a in Figure 4.
- In the case that the above construction of CID is used,
there is produced no gap between the electrodes 7 on the surface of
the substrate 5 in the carrier transfer direction, so that the carrier
transfer efficiency can be improved relatively. However, since poly-
crystalline silicon layer or first electrode 7A exists in the image
sensing cell 9, the light reception is carried out through the polycrystal-
line silicon layer 7A. As a result, there occurs such a disadvantage
that its sens~tivity for the light, especially the light of shor~ wave is
lowered.
OBJECIS AND SUMMARY OF THE INVENTION
Accordingly, it is a rnain object of this invention to pro-
vide a novel solid state image sensor device.
It is another object of the invention to provide a solid
state image sensor device, which is of a frame transfer system
employing a CTD, free from the defects encountered in the prior art.
It is a further object of the invention to provide a solid
state image sensor device of the frame transfer system which has a
special construction of image sensing cells.
According to an aspect of the invention, there is provided
, . , . .. - ,
.. .. . . . . -
8~36
a solid state image sensor device which comprises a semiconductor
substrate of one conductivity type, an insuI~ting layer formed on a
first surface of said substrate, a plurality of channel stopper regions
of said one conduclivity type formed in said substrate in faced re-
lation to its first sul~ace, said channel stopper regions being extended
in the column direction with a distance between adjacent ones, a
plurality of sets of electrodes formed on said insulating.layer, each
set of electrodes including a pair of electrode m~mbers, each of
said electrode members being extended in the row direction, and a
plurality of window portions formed in said pair of electrode members
at one side of the distance between adjacent channel stopper regions.
More particularly, there is provided:
a solid state image sensor device comprising:
a) a semiconductor substrate;
b) an insulating layer formed on a first surface of said
substrate;
c) a plurality of channel stopper re~ions formed in said
substrate adjacent to said first surface, said channel
. . ,. .~_.. ,.. ,,. . , .. = . .
stopper regions extending in parallel in a first
direction with a distance between adjacent channel
stopper regions definina transfer channels therebetween;
d) a plurality of sets of electrodes formed on said
insulating layer, each set of which includes a first
electrode member and a second electrode member, a
second insulating layer separatina said second electrode
member from said .first electrode member, each of said
electrode members extending in a second direction
transverse to said first direction, said second electrode
members along said extending direction overlapping an
adjacent side of said first electrode member; and
1C)7C~1~06
) a pl.urality of window portions formed through at
laast one of said electrode member of each of said pairs.
The other objects, features and advantages of the invendon
will become apparent frorn the following description taken in conjunction
with the accompanying drawings.
--6--
~07L~306
DESCRIPIION OF THE PREFERRED EMBODIMENTS
An example of the solid state image sensor device,
especially its image sensing cell according to the invention will be
described in detail with reference to Figures 5 to 8.
A semiconductor substrate, for example, silicon substrate
10, which is of one conductivity type, i.e., P (or N-) type and of low
impurity concentration, is prepared. Strip channel stopper regions 11,
which are of high impurity concentration and of the same conductivity
type, i. e., P+ (or N+~ type as the substrate 10, are formed in the
substrate 10 to face its major surface 10a in, for example, the column
direction with a predetermined distance between adjacent ones. An
insulating layer 12 made of SiO2 or the like is coated on the major
surface 10a of the substrate 10. First strip electrode members 13A,
which are made of transparent or opaque conductive layer such as
polycrystalline silicon or metal, for example, aluminum, molybdenum
or the like, are formed on the insulating layer 12 in the direction
intersecting the extending direction of each channel stopper region 11,
that is, in the row direction with a predetermined distance between the
adjacent ones. The first electrode members 13A are shown in Figure
5 with oblique lines sloping downwardly down to the right. Another
insulating layer 14 made of, for example, SiO2 is coated to cover the
surfaces of the electrode members 13A and the portions therebetween,
and second strip electrode members 13B made of the material sub-
stantially the same as that of the first electrode members 13A are
formed between the adjacent first electrode members 13A along the
latter through the insulating layer 14 in such a manner that both sides
:`
, . .
-`8 -
.. . . ..
.6
of the second electrode members 13B along the extending direction
thereof rest on or overlap the adjacent first electrode members 13A.
T~he second electrode members 13B are shown in Figure 5 with oblique
lines sloping downwardly down to the left.
Thus, the CTDs are formed between the adjacent channel
stopper regions 11 in the column direction. In this invention, at the
position displaced to one side in the portion between the adjacent
channel stopper regions 11 or in the portion forming an image sensing
cell or picture element, there is provided a window portion 15 where
no electrode members 13A and 13B exist. The distance d between the
electrode members 13A and 13B is selected to be such a value, for
example, more than 4 ~m ~micron) that the electric field produced
by the electrode 13 does not affect on the surface 10a of the substrate
10 beneath the other electrode 13B. The window portion 15 may be
formed such that it is extended to the middle of the channel stopper
region 11 shown in Figure 5. This window portion 15 serves as an
image sensing cell.
If necessary, an insulating layer 17 made of SiO2 or the
like is coated to cover all the electrode members 13~, and a transparent
electrode 16 such as Nesa is coated on the insulating layer 17 to cover
the latter.
The adjacent first and second electrode members 13A and
13B are electrically connected at, for example, their one ends to form
a transfer electrode 13. Every second transfer electrode 13 thus
formed is made as a set. Upon transferring the carriers, 2-phase
clock pulses ~1 and ~2 are app1ied to the electrode 13 of each set.
- : .. -. . .
~7C~81~)6
The transparent electrode 16 is given a fixed potential such as the
ground potential.
In order to better understand the solid state image sensor
device of the invention described above, one method of making the
same will be described with reference to Figures 9A to 9H.
As shown in Figure 9A, the semiconductor substrate 10
with the channel stopper region 11 (not shown in Figure 9A) is pre-
pared first, and a silicon dioxide SiO2 layer is formed on the surface
of the substrate 10 by the thermal oxidization thereof to form the
insulating layer 12.
Next, as shown in Figure 9B, a si licon layer 20 of low
resistivity is formed on the insulating layer 12 by doping a P-type or
N-type impurity to a polycrystalline silicon layer at high concentration.
Then, the silicon layer or polycrystalline silicon layer 20
is subjected to photo-etching process to remove unnecessary portions
thereof and thus form the first electrode members 13A with the silicon
layer 20 as shown in Figure 9C. At this time, a portion corresponding
to the window portion 15 shown in Figure S is formed in the first
electrode member 13A.
As shown in Figure 9D, the insulating layer 14 made of
SiO2 is formed on all the surface of the elements shown in Figure 9C
by a chemical vapor growth method or thermal oxidization.
As shown in Figure 9E, a polycrystalline silicon layer 21
is formed on the insulating layer 14 by doping an impurity of P-type or
N-type at high concentration thereto.
Then, the polycrystalline silicon layer 21 is subjected to
q
~07(~306
photo-etching process to remove unnecessary portions thereof and
hence to form the second strip electrode rrlembers 13B, as shown in
Figure 9F.
If necessary, an insulating layer 17 is formed to cover
at least the second electrode members 13B by producing SiO2 with
thermal oxidization or the like as shown in Figure 9G.
Further, if necessary, the transparent electrode such as
Nesa layer 16 is coated on the insulating layer 17 as shown in Figure
9H.
The operation of the solid state image sensor device of
the invention described above will be described with reference to
Figures lOA and lOB. During the light receiving period of the image
sensing cell or period r1 in which a charge or carrier pattern in
accordance with a light image to be picked up is produced, one of two
electrode groups made by connecting every second electrode 13 are
supplied with the clock voltage, for example, -lOV (volts) as shown
in Figure 10A, and the other electrode group are kept at OV as shown
in Figure lOB. Thus, the charges or carriers induced in the substrate
10 beneath the respective windows 15 formed in the ~lectrodes 13 are
supplied with the voltage of -lOV during the light receiving period rl,
then transferred to the parts of the substrate lO beneath the electrodes
13 of the electrode group which establish a potential well (not shown)
in the substrate lO and stored therein. Accordingly, if the adjacent
2-phase clock voltages 01 and ~2 are supplied to the electrodes during
the next transfer period r2, the stored carriers are transferred
successively to the adjacent electrodes 13 in one direction and then to
~.~7~306
the storage array which was described in connection with Figure 1.
In this case, if the window portion 15 is formed to extend to or partially
overlap the channel stopper region 11, this portion can be used as an
image sensing cell also.
With the solid state image sensor device of the invention
described above, no electrode 13 presents at the portion for receiving
the light image, so that there is no defect that the light receiving
sensitivity is lowered or infringed by the electrode 13, especially for
light of short wave length. In addition, at the portions of the re-
spective electrodes 13 other than the window portions 15 or the portions
serving as the carrier transfer channels, there are no gaps there-`
between, so that the carrier transfer efficiency is improved.
In general, the carrier transfer e~ficiency is not propor-
tional to the width of the carrier transfer channel in the first degree
function, but when the width of the transfer channel is decreased, the
transfer efficiency is lowered abruptly.
According to the solid state image sensor device of the
invention, since the window portion 15 is provided at the position dis-
placed to one side of the portion between the adjacent channel stopper
regions 11, the effective width of the transfer channel portion can be
made wide. This causes the transfer efficiency to be improved also.
If the distance d of the window portion 15 between the
electrodes 13 is selected too small or smaller than a predetermined
value, for example, 4~-m, there may occur the fear that the carrier
transfer is caused in the window portion 15. In this case, the carrier
passing through this window portion is hard to affect by the voltage of
- . . .
. . , ,. : ;; . ..................... .
. . - .
107~8~6
the electrode 13 but is apt to be affected by the SiO2 layer on the
window portion 15 on which no electrode exists. As a result, the
transfer efficiency becomes dif~ferent at positions. For this reason,
a uniform picture can not be obtained and also resolution is deteriorated.
Therefore, it is desired that the distance d is selected greater than a
predetermined value.
The above expression is given on the example where 2-
phase clock type is employed. The case where 3-phase clock type is
employed will be described with reference to Figures 11 and 12, in
which the like numerals indicate the like elements and which also
belongs to this invention.
In this case, the insulating layer 12 made of SiO2 or the
like is also formed on one major surface lOa Oe the semiconductor
substrate 10 with the channel stopper regions 11, and a layer of high
resistivity such as an intrinsic polycrystalline silicon layer 22 is
formed on all the surface of the insulating layer 12, and a P-type or
N-type impurity is selectively doped at high concentration in the layer
22 by, for example, diffusion to form the electrodes 13. In this case,
a semi-insulating layer 23 made of parts of the poly~rystalline silicon
layer 22 is interposed between the adjacent electrodes 13, and also
parts of the layer 22 are removed by the photo-etching to form the
window portions 15. Every third electrode 13 is electrically connected
to form three sets of electrode group and the three sets of electrodes
are supplied with 3-phase clock 01~ 02 and 03 upon the carrier
transfer.
With the solid state image sensor device of the invention
.. 1~
.
- ,' ' , ;,
.: - . ,
107~06
described just above, the receiving of light is carried out through the
window portion 15 formed in the electrode 13 also, so that the light
receiving sensitivity can be improved especially in light of short wave
length as compared with the case where the light is received through
the electrode made of polycrystalline silicon. Further, since the
semi-insulating layer 23 is interposed between the adjacent electrodes
13 other than the window portion 15, no substantial gap exists be-
tween the electrodes 13 and hence the carrier transfer efficiency is
high.
It will be apparent that many modifications and variations
could be effected by one skilled in the art without departing from the
spirit or scope of the novel concepts of the present invention, so
that the scope of the invention should be determined by the appended
claims
~'~ ~
