Photo semiconductor integrated circuit device and optical...

Details Photo semiconductor integrated circuit device and optical... Photo semiconductor integrated circuit device and optical...

2001-08-06

2003-06-03

Zarabian, Amir (Department: 2822)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Electromagnetic or particle radiation

C257S444000, C257S462000, C257S463000

Reexamination Certificate

active

06573578

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a photo semiconductor integrated circuit device having a photodiode portion and an amplifier portion.
2. Description of the Related Art
A photo semiconductor integrated circuit device having a photodiode portion and an amplifier portion is used for light detection and signal processing, for example, in CD (Compact Disk) drives or DVD (Digital Versatile Disk) drives as optical information recording reproducing apparatus. A semiconductor integrated circuit device and a photodetector have been generally manufactured separately so far and detection signals from a photodiode are sent by way of wirings such as lead wires to the semiconductor integrated circuit device and applied with processing such as amplification. However, in the CD drives, it has been demanded for high-speed operation of reading and size reduction of apparatus, and those referred to as OEIC (Optoelectronic Integrated Circuit Device) in which a photodiode and a semiconductor integrated circuit are prepared on one identical substrate have been manufactured in order to cope therewith. The structure is described for example in JP-A-266033/1999. Further, JP-A-82268/1992 describes a semiconductor device having a semiconductor substrate of a first conduction type and a photodiode constituted with an epitaxial layer of a second conduction type in which a semiconductor region at a concentration lower than an epitaxial layer or the semiconductor surface is formed below the epitaxial layer, or a semiconductor region of a first conduction type at a concentration higher than the semiconductor substrate is formed below the epitaxial layer thereby improving the responsivity and extending the band width of the photodiode.
FIG. 2
is a schematic cross sectional view for one example of a photo semiconductor integrated circuit device with a photodiode prepared on an SOI (Silicon on Insulator) substrate. In
FIG. 2
, are shown a photodiode portion
1
and a transistor portion
2
as a part of an amplifier portion. The devices are prepared on the SOI substrate in which an n-type silicon handle wafer
30
, an oxide layer
40
and a silicon crystal layer (that is, an SOI layer
31
) are formed.
In the transistor portion
2
, a collector
63
, an emitter
64
and a base
65
are formed on a passivation layer
43
. An n
−
type epitaxial layer
32
is present on the SOI layer
32
, and constitutes together with a base diffusion layer
33
and an emitter diffusion layer
35
. A polysilicon layer
34
is provided for leading out the base layer
33
, and an oxide layer
45
is provided on layer
34
. A buried layer
50
as a high concentration impurity layer prepared on the surface of the substrate before growing a silicon layer by epitaxial growing, is formed by introducing an impurity into the SOI layer
31
for lowering the collector resistance and is connected by way of an n-type diffusion layer
51
for collector junction to an upper electrode (collector). It is conducted with the emitter
64
by way of the emitter diffusion layer
35
, polysilicon
36
for emitter and a silicide layer
66
. A side wall oxide layer
42
insulates polysilicon for the emitter and the base. Devices are separated from each other by an inter-device isolating buried oxide layer
41
and intra-device isolation is attained by buried oxide layer
46
as a shallow groove.
In the photodiode portion
1
, are shown a cathode electrode
61
and an anode electrode
62
of the photodiode. Light
10
to be detected transmitting the oxide layer
44
generates carriers in a p
+
layer
37
, an epitaxial layer
32
, and a buried layer
50
to form an photo current between the electrodes
61
and
62
. A polysilicon layer
34
is provided for leading out the p
+
layer
37
. The photodiode has a buried layer
50
as in the case of the transistor and is connected to the cathode electrode (upper electrode)
61
by way of an n-type diffusion layer
52
and a suicide layer
67
for cathode connection. Although not illustrated in this example, current from the photodiode is put to signal processing by a group of transistor integrated circuits.
In the photodiode portion
1
, are shown a cathode electrode
61
and an anode electrode
62
of the photodiode. Light
10
to be detected transmitting the oxide layer
44
generates carriers in a p
+
layer
37
, an epitaxial layer
32
, and a buried layer
50
to form an photo current between the electrodes
61
and
62
. The photodiode has a buried layer
50
as in the case of the transistor and is connected to the cathode electrode (upper electrode)
61
by way of an n-type diffusion layer
52
and a silicide layer
67
for cathode connection. Although not illustrated in this example, current from the photodiode is put to signal processing by a group of transistor integrated circuits.
FIG. 3
shows the change of intensity of light in the inside of silicon when silicon crystals are irradiated. The intensity of light is normalized by the intensity at the surface. While the intensity of light decays as the depth increases from the surface and the state of decay is different depending on the wavelength of light. Near the wavelength at 780 nm used in CD drives, light intrudes deeply as far as the inside of the silicon crystals but light at a shorter wavelength of 410 nm is substantially decayed near the surface. Further, the intrusion state of light at a wavelength of 660 nm used in DVD drives situates between both of them.
The light intruding to the inside of silicon generates carriers to form photocurrent. The relation between the state of generation of carriers and the structure of the photodiode constitutes a factor determining the responsivity of the photodiode and the frequency response.
FIG. 3
shows an example of a size for the cross sectional structure of a photodiode. PD layer shows a range from p
+
layer at the surface of the photodiode to a depletion layer end including an n
−
layer. SOI layer is a silicon crystal layer in which a buried layer is formed. A reverse bias is applied at a sufficient level to the SOI layer relative to the PD layer and the depletion layer reaches as far as the SOI layer. At the wavelength of 410 nm shown by the solid line, since almost of light is absorbed in the PD layer, the cutoff frequency is determined by the drifting speed of the carriers and it is expected to be a cutoff frequency at about Giga Hz. On the other hand, at a wavelength of 780 nm shown by the short dotted line, the light reaches at a sufficient intensity as far as the SOI layer and further reaches as far as the handle wafer. Since a voltage is not applied in the SOI layer as in the depletion layer, the photo generated carriers form a photocurrent through the diffusion process. Since the diffusion process is an extremely slow process, the frequency band width of the photodiode is remarkably narrowed as the ratio of this current increases.
Further, the photodiode responsivity can be improved when more photo generated carriers enter the depletion layer. In the photodiode using the SOI substrate, since it is separated by an insulator from the handle wafer, photo-carriers generated in the handle wafer do not contribute to the photo-current of the photodiode. Accordingly, in a case where a great amount of light intrudes through the oxide layer into the handle wafer as in the case of the light at 780 nm shown in
FIG. 3
, photodiode of higher responsivity is no more obtainable.
At present, high-speed readout has been demanded in compact disk drives or digital versatile disk drives and higher responsivity and broader band width are required for the photodiode. However, while the production process is optimized to the integrated circuit device portion, when the cutoff frequency or the responsivity of the photodiode is intended to be improved by changing the thickness of the SOI layer and the thickness of the PD layer, the performance of the integrated circuit device portion such as for transistors may possibly be deteriorated.

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