Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
1998-11-06
2001-03-27
Munson, Gene M. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S248000
Reexamination Certificate
active
06207981
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a two-phase charge-coupled device with a single-layered electrode structure where a pair of potential barrier region and a charge storage region are disposed underneath one charge transfer electrode, and more particularly to a method for producing the charge-coupled device.
There are two types of charge-coupled devices: a 2-phase, 2-ply-electrode-type charge-coupled device and a 2-phase, single-ply electrode-type charge-coupled device.
The 2-phase, 2-ply electrode type charge-coupled device is disclosed in references: JP-A-192561/1992, JP-4133/1986, and IEDM Technical Digest, 1974, pp 55-58. This charge-coupled device is fabricated as follows:
Referring to FIGS.
12
(A) to
12
(E), an N-type semiconductor region
702
is first formed on a P-type semiconductor substrate
701
. Then, a first insulating film
703
is formed on the surface of the N-type semiconductor region
702
though a heating process (FIG.
12
(A)).
A first conductive electrode
704
of polycrystalline silicon is formed on the first insulating film
703
(FIG.
12
(B)). As seen in
FIG. 13
, the first conductive electrode
704
has a rectangular top pattern.
FIG. 13
is a schematic plan view corresponding to FIG.
12
(B). The first conductive electrodes
704
are disposed at constant intervals.
Next, impurities (e.g. boron) of a conductivity type opposite to that of the N-type semiconductor region
702
are implanted into regions between the first conductive electrodes
704
, so that a N
−
-type semiconductor region
705
is formed (FIG.
12
(C)).
FIG. 14
is a schematic plan view corresponding to FIG.
12
(C).
In succession, the first insulating film
703
is removed with the first conductive electrode
704
acting as a mask. Thereafter, the intermediate structure is again subjected to a heating process to form the second insulating film
706
. A second conductive electrode
707
of polycrystalline silicon is formed on the second insulating film
706
corresponding to the first conductive electrode
704
and the N
−
-type semiconductor region
705
(FIG.
12
(D)).
FIG. 15
is a schematic plan view corresponding to FIG.
12
(D).
Next, an interlayered insulating film
708
is disposed. Electrodes are interconnected with metal conductors
709
(FIG.
12
(E)). Thus, a conventional 2-phase, 2-ply electrode charge-coupled device is fabricated.
The progress of the micro patterning technique has allowed a single-ply electrode-type charge-coupled device with a electrode spacing of 0.2 to 0.3 &mgr;m to be fabricated by etching single-ply conductive electrode materials.
The charge-coupled device with the single-ply electrode structure has no electrode portions overlapped. This structure provides a small capacitance between layers and raises no insulation fault between electrodes. Moreover, the oxidizing process is not required to form the interlayered film. This allows metal films or silicide films to be used as an electrode material, instead of the polycrystalline silicon, so that the resistance component of the electrode can be decreased.
The 2-phase, single-ply electrode type charge-coupled device is fabricated according to the FIGS.
16
(A) to
16
(D).
An N-type semiconductor region
802
is first formed on a P-type semiconductor substrate
801
. Then, the intermediate structure is subjected in a heating process to form an insulating film
803
on the surface of the N-type semiconductor region
802
(FIG.
16
(A)).
Next, impurities (e.g. boron) of an opposite conductivity type to the second conductivity type of the N-type semiconductor region
802
are implanted with a photoresist in a predetermined pattern acting as a mask. Thus, the N
−
-type semiconductor region
805
is formed (FIG.
16
(B)).
FIG. 17
is a schematic plan diagram corresponding to FIG.
16
(B).
In succession, a conductive electrode
804
of a polycrystalline silicon is formed on the insulating film
803
(FIG.
16
(C)). The conductive electrode
804
is patterned so as to have a pair of a charge storage region and a potential barrier region. FIG.
16
(C) is a schematic plan diagram corresponding to FIG.
16
(C).
Next, an interlayered film
808
is formed on the surface of the intermediate structure. Electrodes are interconnected with metal conductors
809
(FIG.
16
(D)).
Thus, a conventional 2-phase drive type charge-coupled device with a single-ply electrode structure can be obtained.
On the other hand, in the 2-phase, 2-ply electrode type charge-coupled device, the potential barrier region is self-aligned with the charge transfer electrode and is formed in a rectangular pattern. In this structure, it has been difficult to provide a potential distribution sloped in the charge transfer direction to facilitate the charge transfer.
JP-A-192561/1994 discloses a solid-state image pickup device having slanted electrode patterns. However, even in this image pickup device, since the potential in the charge storage region becomes shallow gradually in a charge transfer direction, the advantages of the present invention cannot be obtained.
Moreover, the same problem arises in the above-mentioned single-ply electrode, 2-phase drive charge transfer device.
SUMMARY OF THE INVENTION
The objective of the present invention is to solve the above-mentioned tasks.
Moreover, the objective of the invention is to provide a charge-coupled device that can smoothly transfer electric charges.
Furthermore, the objective of the present invention is to provide a method for producing a charge-coupled device that can smoothly transfer electric charges.
The objective of the present invention is achieved by a charge-coupled device comprising a first conductivity-type semiconductor layer; a charge transfer electrode formed on the first conductivity-type semiconductor layer; and a potential barrier region and a charge storage region formed in the first conductivity-type semiconductor layer underneath the charge transfer electrode, wherein the charge storage region is formed in such a manner that the potential P(x) in the charge storage region at a point a distance x in the charge storage region apart in a charge transfer direction from the boundary between the potential barrier region and the charge storage region is a monotone decreasing function when a voltage is applied to the charge transfer electrode.
Moreover, according to the present invention, a charge-coupled device comprises a first conductivity-type semiconductor layer; a charge transfer electrode formed on the first conductivity-type semiconductor layer; and a potential barrier region and a charge storage region formed in the first conductivity-type region underneath the charge transfer electrode, wherein the charge storage region is formed in such a manner that the cross area of the charge storage region at a point a distance x in a charge transfer direction from the boundary between the potential barrier region and the charge storage region is a monotone increasing function when the charge storage region is cut perpendicularly to the charge transfer direction.
Particularly, in a charge-coupled device comprising a first conductivity-type semiconductor layer, a charge transfer electrode formed on the first conductivity-type semiconductor layer, and a potential barrier region and a charge storage region formed in the first conductivity-type semiconductor layer underneath the charge transfer electrode, the charge storage region is formed in such a manner that the potential P(x) in the charge storage region at a point a distance x in a charge transfer direction from the boundary between the potential barrier region and the charge storage region is a monotone decreasing function when a voltage is applied to the charge transfer electrode and in such a manner that the cross area of the charge storage region at a point a distance x in a charge transfer direction from the boundary between the potential barrier region and the charge storage region is a monotone increasing function when the charge storage region is cut perpendicularly to the char
Hatano Keisuke
Nakashiba Yasutaka
Hayes Soloway Hennessey Grossman & Hage PC
Munson Gene M.
NEC Corporation
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