Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2000-11-14
2001-11-06
Fahny, Wael (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S031000, C438S032000, C438S060000, C438S069000, C438S071000, C438S072000
Reexamination Certificate
active
06312969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a solid state imaging sensor, a method for manufacturing the solid-state imaging sensor and an imaging device, and relates in particular to a CCD type solid-state imaging sensor (hereafter CCD solid-state image sensor), a manufacturing method for the CCD solid-state image sensor, and an imaging device incorporating the CCD solid-state image sensor.
2. Description of Related Art
The pixel structure for the CCD solid-state image sensor known in the conventional art is for example shown in the cross section of an essential portion in
FIG. 9. A
line-shaped vertical transfer section
32
is formed at intervals on a silicon (Si) substrate
31
. A line-shaped transfer electrode
33
is formed on the silicon substrate
31
directly above the vertical transfer section
32
. Further, a discrete sensor
34
for performing photoelectric conversion is formed on the silicon (Si) substrate
31
between the lines of the transfer electrode
33
.
A light-impervious film
35
with an aperture is formed directly above the sensor
34
and covers the transfer electrode
33
from above. Light enters the sensor
34
through the aperture
36
of the light-impervious film
35
. This light-impervious film
35
functions to block light from entering any portion other than the sensor
34
. Further, incident light is focused on the sensor
34
by a so-called on-chip lens (OCL)
37
.
In this kind of CCD solid-state image sensor
30
, light enters from the edge of the aperture
36
of the light-impervious film
35
so that light may reflect at the boundary between the light-impervious film
35
and the silicon substrate
31
and a portion of the reflected light may enter the vertical transfer section
32
causing a problem known as “smear”. An overhang
35
a
is installed to project over the bottom of said light-impervious film
35
and over the sensor
34
in order to reduce this smear component. In the conventional art, the focal point for the on-chip lens is for instance brought in proximity to the light-receive surface
34
a
of the sensor
34
by means of the aperture
36
of the light-impervious film
35
, or in other words, formed to be at the same height as the overhang
35
a.
An imaging device known in the conventional art, is shown for instance in the concept structural view of FIG.
10
. An imaging device
50
has an imaging zone
39
with pixels arrayed vertically and horizontally on the silicon substrate
31
, and further has a CCD solid-state image sensor
30
with the above mentioned cross sectional structure for these pixels. Said imaging device is further comprised of a camera lens system
40
comprising a diaphragm
42
and an imaging lens
41
installed above the CCD solid-state image sensor
30
.
However, in the above-mentioned CCD solid-state image sensor
30
, when light passes through the end of the on-chip lens
37
as shown in
FIG. 9
, a problem occurs in that the light A is reflected from the upper end (shoulder portion) of the light-impervious film
35
and exits on the outer side of the on-chip lens
37
and thus cannot enter the sensor
34
as intended. Further, the light B located more towards the center of the on-chip lens
37
than the light A, is reflected from the side surface of the light-impervious film
35
and also reflected from the overhang
35
A for the light-impervious film
35
projecting over the sensor
34
so that light cannot enter the sensor
34
. This problem, as is related later is thought due to the installation of the overhang
35
A height in proximity to the focusing point of on-chip lens
37
. The extent of light reflection at the light-impervious film
35
increases as the light contains more of these oblique light constituents such as the light A and B mentioned above. This increase is particularly drastic when the F number of the camera lens system
40
of the imaging device
50
is set to be a minimum or when the so-called pupil distance s from the diaphragm
42
of the camera lens system
40
to the light-receive surface
34
a
is short.
Whereupon, moving the on-chip lens closer or farther away from the light-receiving surface
34
a
of the sensor
34
was attempted as a countermeasure as well as changing the refraction index of the on-chip lens
70
however a portion of the light input is blocked by the light-impervious film
35
due to the structure of the above-mentioned CCD solid-state image sensor
30
. Also in this structure, during the light entry process, the light C which is not blocked by the light-impervious film
35
is successfully incident upon the light-receiving surface
34
a
however a portion is reflected from the surface of the silicon substrate and does not enter the light-receive surface
34
a.
Thus in the CCD solid-state image sensor
30
of the conventional art, even if light is concentrated with the on-chip lens
37
towards the sensor
34
, this light will be reflected from the surface of the silicon substrate
31
or the light-impervious film
35
and exit on the outer side of the on-chip lens
37
, failing to enter the sensor
34
. In other words, many constituents of the light do not contribute to device sensitivity thus leading to decline in sensitivity in the CCD solid-state image sensor
31
. The light reflected from the surface of the silicon substrate
31
is reported to be
30
percent or more.
Further, when the pupil distance s is short in the camera lens system
40
in the imaging device
50
of the conventional art shown in
FIG. 10
, light from the on-chip lens
37
of the camera lens system
40
will irradiate (be incident upon) the sensor
34
however, as related before this light contains a particularly large amount of oblique light constituents. Also, in
FIG. 10
, from among the input light, the concentrated light E
1
(hereafter referred to as the main light beam) which passes through the approximate center of the diaphragm
42
, tends to spread out in an increasingly large angle from the center of the imaging zone
39
towards the periphery with respect to the light-receive surface
34
a
of the sensor
34
, and when the distance s as shown in the figure is short, the oblique light constituents contained in the input light clearly increase as the light approaches the periphery of imaging zone
39
. Consequently, the focusing point for the light from the on-chip lens deviates a slight amount at a time from the pixels at the approximate center of the aperture
36
of the light-impervious film
35
as the light shifts from the center of the imaging zone
39
towards the periphery. The focusing efficiency on the sensor
34
of the imaging zone
39
in particularly declines along with a drop in sensitivity and the problem of shooting occurs.
In order to resolve these problems, the conventional art attempted shifting the position of the on-chip lens
37
a slight amount at a time from the center of the imaging zone
39
and towards the periphery, thus offsetting or compensating the input light position according to the distance s as shown in
FIG. 11
, in an enlarged cross section (b) of an essential portion of FIG.
10
. However, in this case also, the light E passing the end of the on-chip lens
37
is reflected from the upper edge of the light-impervious film
35
and cannot enter the sensor
34
due to the reason related before in which the focus point of the on-chip lens
37
is located near the same height as the overhang
35
a
. This method thus failed to adequately improve light focusing efficiency.
However as increasing progress is made in miniaturizing pixel size along with greater compactness of the CCD solid-state image sensor
30
, the need for setting the physical thickness of the light-impervious film
35
to a certain extent vertically becomes more essential however, making the light-impervious film
35
thinner is difficult. Further, the smear constituents cannot be increased so that a covering for the light-impervious film
35
above sensor
34
is needed, in other words making an overhang
3
Fahny Wael
Sonnenschein, Nath & Rosentahl
Sony Corporation
Toledo Fernando
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