Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1999-04-08
2001-06-26
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S232000, C257S233000, C348S297000, C348S298000, C438S060000, C438S075000
Reexamination Certificate
active
06252285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state imaging device and an inspection method and a production method of the same, and more particularly to a solid state imaging device having on-chip microlenses and an inspection method and a production method of the same.
2. Description of the Related Art
In recent years, there have been increasingly developed solid state imaging devices for video cameras and image input cameras for personal computers. With the popularization of a solid state imaging device, higher performances have been required for it. In particular, increase of the number of pixels and miniaturization of solid state imaging device are essential problems to be tackled for the development. For example, as regards increase of the number of pixels, the number of pixels in a digital still camera application which has become popularized recently appears to increase from 330,000 pixels (640 dots by 480 dots) to 1,300,000 pixels (1,280 dots by 1,024 dots). Meanwhile, as regards miniaturization, in a solid-state imaging device of the class of 330,000 pixels, the main current till now appears to change from a ⅓ inch format (5.5 mm diagonally) to a ¼ inch format (4 mm diagonally).
Such increase of the number of pixels and miniaturization of a solid-state imaging device force reduction of the pixel size. In the aforementioned solid-state imaging device of the class of 330,000 pixels, if a pixel is of a square shape, one side of the pixel is approximately 6.8 &mgr;m in the ⅓ inch format, while one side of a pixel is 5.0 &mgr;m in the ¼ inch format. As the pixel size decreases, the mount of incident light also decreases, resulting in a drop in the sensitivity. This deteriorates the SN ratio and hence deteriorates the picture quality. Therefore, there arises a problem how to attain a high sensitivity even when the pixel size is small. In order to solve the problem, a construction has heretofore been employed wherein an on-chip microlens is formed on a photodiode to increase the light-gathering rate to the photodiode.
A construction of a conventional solid-state imaging device will be described below in detail. First, a conventional popular interline type CCD (Charge-coupled device) imaging device will be described.
Referring to
FIG. 1
, there is illustrated an interline type CCD imaging device which includes an imaging area
101
at a central portion of one major surface of a semiconductor substrate, a horizontal CCD
102
adjacent to imaging area
101
, and an output section (charge detector)
103
for horizontal CCD
102
, and the remaining portion forms a field area
108
. Arranged in a two-dimensional matrix in imaging area
101
are a plurality of photodiodes
104
which are photoelectric conversion elements for converting light into signal charge and storing the signal charge.
A vertical CCD
105
for transferring signal charge in a vertical direction is positioned adjacent each row of photodiodes
104
. A readout area
106
for reading signal charge from photodiode
104
to vertical CCD
105
is provided between each photodiode
104
and adjacent vertical CCD
105
. The portion in imaging area
101
other than the elements described forms an element separation area
107
. Vertical CCDs
105
are connected to horizontal CCD
102
. Though not shown in
FIG. 1
, a light-gathering microlens
119
which will be described later is provided above each of photodiodes
104
.
FIG. 2
shows a cross section of one of pixels of such a CCD imaging device as described above. P-type well
110
is formed on N-type substrate
109
, and N-type photodiode layer (photodiode)
104
which performs photoelectric conversion and stores the resulting signal charge, N-type vertical CCD buried layer
112
for transferring charge in a vertical direction, and a readout area
106
for reading charge from photodiode
104
to vertical CCD buried layer
112
are formed in P-type well
110
. P-type vertical CCD well layer
113
is formed below vertical CCD buried layer
112
, and high concentration P-type impurity layer
114
is formed on a surface of photodiode
104
and in element separation area
107
. Vertical CCD transfer electrode
116
is formed on vertical CCD buried layer
112
with insulating layer
115
interposed therebetween. A light intercepting film
117
is also formed on vertical CCD transfer electrode
116
with insulating layer
115
interposed therebetween, and photodiode
104
has a light intercepting film opening
118
formed thereon. Vertical CCD
105
described above comprises vertical CCD buried layer
112
, P-type vertical CCD well layer
113
, vertical CCD transfer electrode
116
and so forth.
A flattened layer
120
is formed on the semiconductor substrate, on which a light-gathering microlens
119
is formed in register with each light intercepting film opening
118
. Light-gathering microlens
119
serves as a convex lens and gathers incident light
121
to photodiode
104
through light intercepting film opening
118
to thereby achieve improvement of the sensitivity.
FIG. 2
shows a construction having a flattened layer
120
made of a uniform substance, while
FIG. 3
shows a construction of another color imaging device wherein a desired color layer
122
for each pixel is formed in flattened layer
120
. The construction shown in
FIG. 3
is same as that shown in
FIG. 2
except color layer
122
.
A method of forming this imaging device will be described by way of example. As shown in
FIG. 4
, through not described in detail, P-type well
110
, photodiode
104
, vertical CCD buried layer
112
, P-type vertical CCD well layer
113
, high concentration P-type impurity layer
114
and so forth mentioned above are formed on semiconductor substrate
109
semiconductor manufacturing process which is usually employed. Insulating layer
115
is then formed above.
Thereafter, vertical CCD transfer electrode
116
, light intercepting film
117
, light intercepting film opening
118
and so forth are formed as shown in
FIG. 5
, to complete a base of the imaging device. Then, as shown in
FIG. 6
, flattened layer
120
made of, for example, an acrylic resin is formed on the base of the imaging device formed by the semiconductor manufacturing process. For the imaging device of the single plate color type, a desired color layer (color layer of a pigment type material or color layer of a dye type material) is formed for each pixel (however, in an imaging device of any type other than the single plate color type, this color layer
122
may not be formed). Further, in order to keep the flatness after formation of color layer
122
, an additional flattened layer
120
is sometimes formed. Thereafter, as shown in
FIG. 7
, a lithography technique is utilized to pattern a resin, which is made of, for example, an acrylic resin, above each light intercepting film opening
118
, that is, at each portion at which a convex lens is to be formed. This resin forms base material
119
a
of light-gathering microlenses
119
. Thereafter, light-gathering microlenses
119
of the convex lens type having a desired curvature are formed, for example, by heat-reflowing, as shown in
FIG. 3
, to complete the imaging device.
Each light-gathering microlens
119
is shaped in a convex lens configuration and dimensioned such that all incident light
121
may be gathered upon photodiode
104
. For forming light-gathering microlenses
119
, an optical simulation is performed to determine a suitable thickness of flattened layer
120
and a height and a width of light-gathering microlenses
119
. In the manufacturing process, the film thickness of flattened layer
120
and the height of light-gathering microlenses
119
will be controlled by monitoring the film thickness of, for example, an acrylic resin upon application and performing a forming step while confirming that the film thickness is suitable. The convex lens surfaces of light-gathering microlenses
119
are formed in desired shapes by monitoring the shape upon patterning
Furumiya Masayuki
Hara Keiichi
Nakashiba Yasutaka
Yamada Tohru
Yamamoto Katsumi
NEC Corporation
Ngo Ngan V.
Young & Thompson
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