Solid-state imaging device having a light barrier layer

A solid-state imaging device in which a light-barrier layer is formed on transfer electrodes on top of a vertical pixel isolating region by an insulating film. The light-barrier layer is adapted to overlie the lateral sides of the transfer electrodes and the peripheral region of a photosensor region neighboring on the vertical pixel isolating region. By provision of the light-barrier layer, the light incident on the vertical pixel isolating region is stopped to reduce smear charges which might otherwise be intruded into the vertical charge transfer section.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a CCD type solid-state imaging device in which 
signal charges are transferred by means of transfer electrodes. More 
particularly, it relates to an interline transfer or frame interline 
transfer type solid-state imaging device. 
2. Description of the Related Art 
A CCD image sensor usually has a plurality of photosensor regions arrayed 
on the surface of a silicon substrate, and is so constructed that signal 
charges generated in these regions are transferred out of a chip to 
produce image signals. 
This type of the CCD image sensor known in the art is constructed as shown 
in FIG. 1, in which a plurality of photosensor regions 2 consisting of 
n-type impurity-diffusion regions are formed on the surface of a p-type 
silicon substrate 1. Signal charges are generated in each of the these 
photosensor regions 2 isolated from the photosensor regions 2 neighboring 
thereon in the vertical direction or in a direction shown by an arrow V in 
FIG. 1. On top of a region isolating the neighboring photosensor regions 2 
from each other are formed a first transfer electrode layer 4 and a second 
electrode layer 5, with interposition of an insulating layer 3, for 
establishing connection with neighboring vertical charge transfer 
sections. On top of the second transfer electrode 5 is formed an aluminum 
light-barrier layer 7 with interposition of a second insulating layer 6. 
This light-barrier layer 7 is formed for surrounding a region around the 
photosensor region 2 and an aperture 8 formed in the light-barrier layer 7 
faces the photosensor region, 
With this type of the CCD image sensor, the light incident via aperture 1 
is converted in the photosensor region 2 into signal charges which are 
transferred and outputted as image signals. 
The above described conventional CCD image sensor, however, has a drawback 
that low smear cannot be realized due to electrical charges from a 
vertical pixel isolation region 9. 
That is, some of the incident light through aperture 1 is incident 
obliquely to generate signal charges in the vertical pixel isolating 
region 9. The charges thus generated in the vertical pixel isolating 
region 9 descend down the hill of potential towards the vertical charge 
transfer section 10 to flow into the vertical charge transfer section 10, 
thus producing smear to lower the quality of the video signals, 
In the JP Patent Publication KOKAI No. 62-221147 (1987), there is disclosed 
a technique wherein the light-barrier layer is formed up to the lateral 
side of a step region to reduce the smear. However, charge generation in 
the vertical pixel isolating region cannot be suppressed sufficiently by 
simply covering the step region with the light-barrier layer, 
OBJECT AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a solid-state imaging 
device wherein smear due to charges generated in the vertical pixel 
isolating region may be reduced. 
The present invention provides a solid-state imaging device in which a 
light-barrier layer is formed on top of transfer electrodes on a vertical 
pixel isolating region by means of an insulating layer, and in which the 
light-barrier layer is adapted to cover the lateral sides of the transfer 
electrodes and peripheral regions of the photosensor regions neighboring 
on the vertical pixel isolating region. 
With the present solid-state imaging device, the light-barrier layer is 
adapted to cover not only the lateral sides of the transfer electrodes but 
also the peripheral regions of the photosensor regions neighboring on the 
vertical pixel isolating region. Thus the light falling on the vertical 
pixel isolating region is stopped to reduce smear charges which might 
otherwise flow into the vertical charge transfer section,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, a CCD image sensor as a solid-state imaging 
device according to the present invention is hereinafter explained. 
Referring to FIG. 3, the CCD image sensor according to the present 
invention includes a plurality of photosensor regions 12 comprised of 
n-type impurity-diffusion regions arranged on a p-type si 1 icon substrate 
in a matrix configuration, Each photosensor region 12 has a substantially 
square plan configuration. A vertical charge transfer section 21 is 
provided adjacent to each vertical column of the photosensor regions. A 
plurality of such vertical charge transfer sections are provided in 
alternation with the columns of the photosensors in the horizontal 
direction shown by an arrow H in FIG. 3. This vertical charge transfer 
section 21 is adapted for transferring charges in the vertical direction 
shown by an arrow V in FIG. 3. Each vertical charge transfer section 21 is 
electrically connected to the photosensor regions 12 by means of readout 
gates (ROGs) 23 provided between it and the photosensor regions 12. Each 
photosensor region 12 is surrounded by a channel stop region 22 except at 
the readout gate 23. The vertical pixel isolating region 13 between the 
vertically adjoining photosensor regions 12, 12 also forms a part of the 
channel stop region 22. Charge generation at the vertical pixel isolating 
region 13 is prevented as a result of the construction of the 
light-barrier layer 14 which will be explained subsequently. 
On top of the vertical charge transfer section 21 are formed two transfer 
electrode layers 17, 18 for supplying driving signals for transferring 
charges in the vertical direction. The first transfer electrode layer 17 
is formed of polysilicon and arranged on an insulating layer 16 formed on 
the silicon substrate 11. As shown in FIG. 4, the first transfer electrode 
layer has a length in the vertical direction equal to one half the pixel 
length and has a pattern of covering an area between the photosensor 
regions 12, 12 facing each other with the vertical charge transfer section 
21 in-between. This first transfer electrode layer 17 interconnects the 
vertical charge transfer sections 21 on top of the vertical pixel 
isolating region 13 with a pattern commensurate with or finer than the gap 
between the photosensor regions 12, 12 facing each other in the V 
direction. A second transfer electrode layer 18 is partially superimposed 
on the first transfer electrode layer 17 by means of an insulating layer 
19, while being also formed on a silicon substrate 11 by means of the 
insulating layer 16. This second transfer electrode layer 18 is similarly 
formed of polysilicon. The second transfer electrode 18 is of such a 
pattern in which it is of the same width as the first transfer electrode 
layer 17 in the H direction on top of the vertical charge transfer section 
21 and has its both ends in the V direction superimposed on the ends of 
the first transfer electrode layer 17. Meanwhile, on top of the vertical 
pixel isolating region 13, the second transfer electrode layer 18 is of a 
pattern finer than the first transfer electrode layer 17 for 
interconnecting the electrodes on each vertical charge transfer section 
21. 
Both of the first and the second transfer electrode layers 17 and 18, 
having the above described patterns, are coated by the insulating layer 
19. Referring to FIG. 5, a light-barrier layer 14 of aluminum is formed on 
the insulating layer 19. The light-barrier layer 14 is formed over the top 
and lateral sides 24 of the first and second transfer electrode layers 17 
and 18 as far as a peripheral regions 25 of the photosensor regions 12. 
Above all, on the substrate major surface, the light-barrier layer 14 
overlies the peripheral region 25 of the photosensor region 12 by a skirt 
portion 15 projecting from the lateral surface 24. With the skirt portion 
15 partially projecting on the photosensor region 12 as the charge storage 
section, the light about to be incident on the vertical pixel isolating 
region 13 is stopped by the skirt portion 15 for thereby suppressing 
generation of electrical charges in the vertical pixel isolating region 
13. The size of the skirt portion may be set depending on the amount of 
smear charges to be reduced and thus may be arbitrarily set in a range 
size from a size extending only slightly on the photosensor region 12 to a 
size substantially covering the peripheral region 25 of the photosensor 
region 12 to a larger extent. 
Meanwhile, smear charges which might cause deterioration of image signals 
are caused to flow in accordance with a potential from the vertical pixel 
isolating region 13 to the vertical charge transfer section 21, as already 
explained by referring to FIG. 2. At this time, the transfer electrodes 
17, 18 on the vertical pixel isolating region 13 function as gate 
electrodes of a simulated MOS transistor. Thus, for reducing smear, the 
threshold voltage Vth of the MOS transistor is enhanced to prevent the 
hill of potential of the vertical pixel isolating region from being 
shifted readily to a lower value towards the vertical charge transfer 
section V.sub.reg. Specifically, the impurity concentration of the 
vertical pixel isolating region 13 is adjusted to prevent a channel from 
being formed in the vertical pixel isolating region 13 when driving 
signals are supplied to the first transfer electrode layer 17. By such 
enhancement, charges may be prevented from flowing from the vertical pixel 
isolating region 13 into the vertical charge transfer section Vreg for 
realizing low smear.