Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2003-03-17
2004-11-23
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S066000
Reexamination Certificate
active
06821809
ABSTRACT:
This application claims priority to Japanese Patent Application Number JP2002-076081 dated Mar. 19, 2002, which is incorporated herein by reference.
The present invention relates to a Solid State Image Pickup Device and a method of producing a solid state image pickup device for use as various kinds of image sensors and camera modules.
RELATED ART
In recent years, the demand for video cameras and electronic cameras has increased dramatically and these cameras use a CCD type or amplification type solid state image pickup device.
Among these, the amplification type solid state image pickup device (CMOS image sensor) includes on a single semiconductor chip an image pickup pixel portion comprising a plurality of pixels arranged in a two-dimensional form, and a peripheral circuit portion disposed on the outside of the image pickup pixel portion. In each pixel of the image pickup pixel portion, floating diffusion (FD) portion as well as various MOS transistors including a transfer transistor and an amplification transistor are typically provided. In this case, light incident on each pixel is subjected to photo-electric conversion by a photodiode to generate a signal charge, the signal charge is transferred to the FD portion by the transfer transistor, the variation of potential at the FD portion is detected by the amplification transistor, and the detected variation is converted into an electric signal and amplified, whereby signals from each pixel are output through signal wires to the peripheral circuit portion.
In addition, the peripheral circuit portion is provided with a signal processing circuit for applying a predetermined signal processing, for example, CDS (correlative double sampling), gain control, A/D conversion, etc. to the pixel signals from the image pickup pixel portion, and a driving control circuit for controlling the output of the pixel signals by driving each pixel in the image pickup pixel portion, for example, vertical and horizontal scanners, a timing generator (TG), etc.
FIG. 11
is a sectional view showing a device structure in a related-art CMOS image sensor, and shows the structure of one pixel
10
in the image pickup pixel portion and one MOS transistor
20
provided in the peripheral circuit portion.
The pixel
10
in the image pickup pixel portion includes a P type well region
11
on an N type silicon substrate
1
, and a photodiode
12
and an FD portion
13
are provided there. A polysilicon transfer electrode
14
for transfer gate for transferring a signal charge from the photodiode
12
to the FD portion
13
is provided in an upper insulating layer
2
of the N type silicon substrate
1
, metallic wirings
15
and
16
formed of aluminum or the like are provided on the upper side of the polysilicon transfer electrode
14
, and, further, a light-shielding film
17
having a light receiving opening portion for the photodiode
12
is provided on the upper side of the metallic wirings
15
and
16
.
In addition, a passivation film
3
comprised of a silicon nitride film or the like is provided on the upper insulating layer
2
, and an on-chip color filter
28
and an on-chip micro-lens
19
are provided on the upper side of the passivation film
3
.
On the other hand, the MOS transistor
20
in the peripheral circuit portion is provided with a P type well region
21
on the N type silicon substrate
1
, and a source region
22
and a drain region
23
are provided there. The upper insulating layer
2
of the N type silicon substrate
1
is provided with a polysilicon gate electrode
24
of the MOS transistor
20
, metallic wirings
25
,
26
and
27
formed of aluminum or the like are provided on the upper side of the polysilicon gate electrode
24
, and, further, a metallic wiring
28
formed of aluminum or the like is provided also in the passivation film
3
on the upper side of the metallic wirings.
In the solid state image pickup device as described above, each pixel is so constructed that in order to enhance the numerical aperture of the photodiode
12
(the ratio of the incident light on the photodiode
12
to the incident light on the pixel), the incident light is condensed on the photodiode
12
through the portion between the wirings by a micro-lens
19
.
In this case, however, a part of the light condensed by the micro-lens
19
is repelled by the wirings
15
and
16
. This causes the following undesired problems.
(1) Sensitivity is lowered as much as the amount of the light repelled by the wirings.
(2) A part of the light repelled by the wirings enters into the photodiode of the adjacent pixel, resulting in mixture of colors.
(3) Since the layout of the wirings is restricted, characteristics are lowered by the limitations such that the wirings cannot be located on the upper side of the photodiode, or thick wirings cannot be utilized.
(4) Miniaturization is difficult to achieve for the same reason as (3) above.
(5) Since skew incidence of light occurs and the proportion of the light repelled is higher at the pixels in a peripheral area, dark shading occurs more heavily in the peripheral area.
(6) When it is intended to produce the CMOS image sensor by an advanced CMOS process in which the number of the wiring layers is increased further, the distance from the micro-lens to the photodiode is enlarged, and the above difficulties are further increased.
(7) Due to (6) above, the typical advanced CMOS processing techniques cannot be used, correction of the layout of the circuits registered in the library is needed, or the number of the wiring layers is limited and therefore the area is enlarged, so that the cost is raised. Besides, the pixel area per pixel is also increased.
In addition, when long-wavelength light such as red light is subjected to photo-electric conversion in the P type well region
11
deeper than the photodiode
12
, the electrons generated diffuse into the P type well region
11
, resulting in that the electrons enter into the photodiode
12
located at another position to cause mixing of colors. When the electrons enter into a pixel light-shielded for detection of black, the black level is detected erroneously.
Besides, while there is a process in which a silicide is used for the active region, the silicide hampers the incidence of light, so that a process of removing only the silicide on the photodiode
12
must be added.
Therefore, the number of steps is increased, and the process becomes complicated. In addition, defects in the photodiode arise from the steps, also.
Furthermore, such functions as a camera signal processing circuit and a DSP which have hitherto been composed of other chips are mounted on the peripheral circuit portion of the CMOS image sensor, as described above. As to these, since the process generation is advanced in the manner of 0.4 &mgr;m→0.25 &mgr;m→0.18 &mgr;m→0.13 &mgr;m, the CMOS image sensor itself must be made to correspond to these new processes; if it is not fulfilled, the merits of miniaturization cannot be offered and the abundant library and knowledge of CMOS circuits cannot be utilized.
However, the number of layers in the wiring structure increases as the process generation advances. For example, while three wiring layers are used in the 0.4 &mgr;m process, eight wiring layers are used in the 0.13 &mgr;m process. In addition, the thickness of the wiring layer is also increased, and the distance from the micro-lens to the light receiving surface of the photodiode is increased by a factor of 3 to 5.
Therefore, in the related-art method in which the light is passed to the light-receiving surface through the wiring layers, it has come to be impossible to efficiently condense the light onto the light-receiving surface of the pixel, and the problems of (1) to (7) above have come to be conspicuous.
Meanwhile, recently, the so-called back-illuminated type solid state image pickup device in which the light-receiving surface of the photodiode is provided on the back side of a semiconductor chip has been proposed as a solid state image pickup device other than the above-mentioned
Abe Takashi
Fujita Hiroaki
Funatsu Eiichi
Mabuchi Keiji
Nakamura Nobuo
Chaudhari Chandra
Depke Robert J.
Holland & Knight LLP
Sony Corporation
Vesperman William
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