Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2003-03-21
2004-12-07
Pham, Hoai (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S557000, C257S577000
Reexamination Certificate
active
06828644
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application No. 2002-81041, filed on Mar. 22, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
A) Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device with reduced parasitic capacitance between two adjacent impurity diffusion regions formed in a semiconductor substrate.
B) Description of the Related Art
FIG. 11A
is a cross sectional view of a photodiode which is one kind of a photo sensor. On the surface of a p-type silicon substrate
100
, an epitaxial layer
101
made of n-type silicon is formed. On the surface of the n-type epitaxial layer
101
, a field oxide film
102
is formed to define a plurality of active regions.
In one active region (an active region in the central area of FIG.
11
A), a plurality of n-type cathode regions
103
are formed mutually spaced apart by a certain distance. Between two adjacent cathode regions
103
, a p-type separation region
104
is formed. The surface of the active region
104
in which the cathode regions
103
and separation region
104
are formed is covered with an antireflection film
105
.
In each of the active regions (active regions on the right and left sides in
FIG. 11A
) adjacent to the active regions in which the cathode regions
103
are formed, a p-type anode lead region
106
is formed. The bottom of the anode lead region
106
reaches the p-type silicon substrate
100
.
The cathode region
103
and p-type silicon substrate
100
constitute a photodiode. The p-type silicon substrate
100
functions as the anode of the photodiode.
Such photodiodes are widely used as an optical pickup device to be used with a photoelectric conversion device typically an optical disc such as a DVD and a CD, as a photo sensor having a photoelectric conversion function. A photo sensor to be used with an optical disc is desired to operate at high speed as the wavelength of a laser beam becomes shorter. In order to realize stable high-speed operation, it is desired to reduce various types of parasitic capacitances in the photo sensor and prevent leak currents.
The photo sensor shown in
FIG. 11A
has parasitic capacitances between the cathode region
103
and adjacent anode region
106
, between the cathode region
103
and p-type silicon substrate
100
and between the cathode region
103
and separation region
104
. These parasitic capacitances are desired to be reduced in order to ensure stable high-speed operation.
FIG. 11B
is a cross sectional view of a conventional photo sensor whose parasitic capacitance is partially reduced. Between the cathode region
103
and anode lead region
106
, a trench
108
is formed through the field oxide film
102
, the trench reaching the surface layer of the p-type silicon substrate
100
. A silicon oxide film is formed on the bottom and inner sidewalls of the trench
108
, and polysilicon is filled in the trench
108
.
A p-type high impurity concentration region
109
is formed in a region of the p-type silicon substrate
100
and n-type epitaxial layer
101
in contact with the trench
108
. This p-type high impurity concentration region
109
prevents leak current from flowing via the bottom of the trench
108
.
Since the thin silicon oxide film having a dielectric constant lower than that of silicon is formed on the sidewall of the trench
108
, parasitic capacitance between the cathode region
103
and anode lead region
106
can be reduced.
Although the parasitic capacitance between the cathode region
103
and anode lead region
106
of the photo sensor shown in
FIG. 11B
can be reduced, the parasitic capacitances between the cathode region
103
and p-type silicon substrate
100
and between the cathode region
103
and separation region
104
cannot be reduced.
Since the p-type high impurity concentration region
109
is formed around the trench
108
, parasitic capacitance is newly formed between the cathode region
103
and p-type high impurity concentration region
109
.
SUMMARY OF THE INVENTION
An object of this invention is to provide a semiconductor device with reduced parasitic capacitance between two impurity diffusion regions having opposite conductivity types.
According to one aspect of the present invention, there is provided a semiconductor device comprising: an underlying substrate having at least a surface layer made of semiconductor of a first conductivity type; a first layer formed on or over the underlying layer and made of semiconductor having a resistance higher than a resistance of the surface layer of the underlying substrate; a first impurity diffusion region formed in a partial surface region of the first layer and doped with impurities of a second conductivity type opposite to the first conductivity type, the first impurity diffusion region not reaching a surface of the underlying substrate; a second impurity diffusion region of the second conductivity type disposed in the first layer and spaced apart from the first impurity diffusion region in an in-plane direction by a certain distance, the second impurity diffusion region reaching the surface of the underlying substrate; and a first separation region disposed between the first and second impurity diffusion regions and comprising a trench formed in the first layer and dielectric material disposed at least in a partial internal region of the trench.
The first layer having a high resistance is disposed between the first impurity diffusion region and underlying substrate. Parasitic capacitance between the first impurity diffusion region and underlying substrate can therefore be reduced. Since the dielectric material is disposed in the trench constituting the first separation region, parasitic capacitance between the first and second impurity diffusion regions can be reduced.
REFERENCES:
patent: 5500550 (1996-03-01), Morishita
patent: 6229194 (2001-05-01), Lizotte
patent: 62-86756 (1987-04-01), None
patent: 3-89550 (1991-04-01), None
patent: 7-45912 (1995-02-01), None
patent: 2000-156521 (2000-06-01), None
Asano Yuji
Fukushima Toshihiko
Katou Morio
Natsuaki Kazuhiro
Setoyama Takao
Fujitsu Limited
Pham Hoai
Westerman Hattori Daniels & Adrian LLP
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