Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-08-18
2002-04-23
Bowers, Charles (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S293000, C257S290000, C369S044120
Reexamination Certificate
active
06376871
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-235760 filed Aug. 23, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device having a photodetector and an optical pickup system using the semiconductor device.
A photodiode as a photodetector capable of converting a light signal into an electric signal has been extensively used for optical sensors for controlling various kinds of photoelectric converters, for example, an optical sensor for obtaining a recording information signal (hereinafter, referred to as “RF signal”), a tracking error signal, a focusing error signal, and the like in a so-called optical pickup system for recording and/or reproducing light signals on and/or from an optical recording medium.
A photodetector is formed, together with various circuit elements such as a bipolar transistor, resistance, and capacitor, on a common semiconductor substrate, to be thus configured as a so-called photo-IC (Integrated Circuit). Such a photo-IC is generally fabricated in accordance with a method of fabricating a bipolar transistor as one of the above-described circuit elements.
As a photo-IC having a fast, high-sensitive photodetector, there has been proposed a photo-IC including a high resistance expitaxial semiconductor layer.
FIG. 5
is a schematic sectional view showing a prior art photo-IC on which a photodiode PD as a photodetector and a bipolar transistor TR are mixedly formed. The photo-IC shown in
FIG. 5
has a configuration of a bipolar IC on which an npn type transistor TR and an anode common type photodiode PD are formed on the same semiconductor substrate
1
.
The method of fabricating the bipolar IC will be described below. A high impurity concentration p-type buried layer
3
is formed on the entire principal plane of a p-type Si semiconductor base substrate
2
, and a low impurity concentration p-type first semiconductor layer
31
for forming an anode region
4
of the photodiode PD is formed on the buried layer
3
by epitaxial growth. A high impurity concentration collector buried region
5
is formed on a transistor TR formation area of the first semiconductor layer
31
. High impurity concentration buried isolation regions
6
are selectively formed in order to isolate circuit elements from each other and to divide the photodiode PD into parts (as will be described below). A high impurity concentration p-type buried region
8
is formed, simultaneously with the formation of the buried isolation regions
6
, under a contact of an anode electrode
7
of the photodetector PD.
A low impurity concentration n-type second semiconductor layer
32
for forming a cathode region
9
of the photodiode PD and a collector region
10
of the transistor TR is formed on the first semiconductor layer
31
by epitaxial growth.
In this way, the first and second semiconductor layers
31
and
32
are formed on the semiconductor base substrate
2
by epitaxial growth, to form an Si semiconductor substrate
1
. Insulating isolation layers
11
made from SiO
2
are formed, by a so-called LOCOS (Local Oxidation of Silicon), on the surface of the Si semiconductor substrate
1
, that is, on the second semiconductor layer
31
in order to electrically isolate semiconductor circuits elements or regions from each other.
In the second semiconductor layer
32
, a high impurity concentration p-type isolation region
12
is formed between the insulating isolation layer
11
and the buried isolation region
6
positioned thereunder at each insulating isolation portion between adjacent circuit elements. A high impurity concentration p-type anode electrode extraction region
13
is formed on the high impurity concentration buried region
8
, and a high impurity concentration anode contact region
14
is formed on the anode electrode extraction region
13
. A high impurity concentration p-type division region
30
is formed on the buried region
6
, which is formed at the division region for dividing the anode region
4
into two parts, in such a manner as to be in contact with the region
6
.
A high impurity concentration n-type collector electrode extraction region
15
and a p-type base region
16
are formed in the collector region
10
. An n-type emitter region
17
is formed on the base region
16
.
A high impurity concentration cathode region
18
is formed on each cathode region
9
of the photodiode PD, and a cathode electrode
19
is in ohmic-contact with the cathode region
18
.
An insulating layer
21
made from SiO
2
is deposited on the surface of the semiconductor substrate
1
, and electrode contact windows are formed in the insulating layer
21
. An emitter electrode
20
E, a base electrode
20
B, and a collector electrode
20
C of the transistor TR are brought into contact with the regions
15
,
16
and
17
through the electrode contact windows, and an interlayer insulating layer
22
made from SiO
2
is formed thereon. A light shading layer
23
made from Al, which has a light receiving window, is formed on the interlayer insulating layer
22
, and a protective layer
24
is formed thereon.
The photodiode PD is irradiated with a light ray to be detected through the light receiving window of the light shading layer
23
. In this case, the insulating layers
21
and
22
act as a reflection preventive film.
The photodiode PD configured as the bipolar IC thus fabricated is used as a sensor for obtaining an RF signal, a tracking error signal, and a focus error signal in an optical pickup system for recording and/or reproducing light signals on and/or from an optical recording medium.
FIG. 6A
shows a plane pattern of a photodiode PD used as a sensor for obtaining an RF signal, a tracking error signal, and a focus error signal in an optical pickup system. In this example, the photodiode PD includes a central photodiode PD
0
divided into four parts A, B, C and D in a cruciform and side photodiodes PD
S1
and PD
S2
disposed on both the sides of the central photodiode PD
0
. Such a photodiode PD is irradiated with light from an optical recording medium, typical, an optical disk in such a manner that a central light spot SP
0
is formed on the central photodiode PD
0
, and side spots SP
S1
and SP
S2
are formed on the side photodiodes PD
S1
and PD
S2
, respectively. In this case, assuming that the outputs obtained by photoelectric conversion at the four divided parts A, B, C and D of the central photodiode PD
0
are taken as outputs A, B, C and D, the focus error signal is obtained by calculating an equation of (A+C)−(B+D), and assuming that the outputs from the side photodiodes PD
S1
and PD
S2
are taken as outputs E and F, the tracking error signal is obtained by calculating an equation of (E−F), and the signal readout signal, that is, RF signal is obtained by calculating an equation (A+B+C+D).
FIG. 6B
shows another example of a photodiode PD applied to an optical pickup system. In this example, the photodiode PD includes a photodiode PD
1
divided in parallel into four parts A, B, C and D in which the center side divided parts B and C are each formed into an extremely thin stripe pattern with a pitch of 14 &mgr;m, and a photodiode PD
2
divided in parallel into four parts A′, B′, C′ and D′ in which the center side divided parts B′ and C′ are each formed into an extremely thin stripe pattern with a pitch of 14 &mgr;m. Such a photodiode PD is irradiated with light in such a manner that a light spot SP
1
is formed on the photodiode PD
1
and a light spot SP
2
is formed on the photodiode PD
2
. In this case, assuming that the outputs from the divided parts A, B, C and D of the photodiode PD
1
are taken as outputs A, B, C, and D and the outputs from the divided parts A′, B′, C′ and D′ of the photodiode PD
2
are taken as outputs A′, B′, C′ and D′, the focus error signal is obtained by
Finsmith David C
Sonnenschein Nath & Rosenthal
Sony Corporation
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