JPH04267561A - Photo semiconductor device - Google Patents

Abstract

PURPOSE:To form an IC comprising a photodiode (21) which ensures quick response by sequentially stacking a non-doped first epitaxial layer (24) and an N-type second epitaxial layer (25). CONSTITUTION:A non-doped first epitaxial layer (24) and an N-type second epitaxial layer (25) are sequentially stacked on a P-type substrate (23) and these are isolated like islands with a P<->type isolating region (26) provided perfectly through such layers. An N<->type diffused region (30) is formed on the surface of the second epitaxial layer (25) to form a photodiode (21) and a P type base region (35) and an N<+>type emitter region (36) are also formed thereon to obtain an NPN transistor (22).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device that integrates a photodiode and a bipolar IC.

0002

[Prior Art] Optical semiconductor devices in which a light-receiving element and peripheral circuitry are integrated and formed monolithically are expected to reduce costs, unlike hybrid ICs in which the light-receiving element and circuit elements are made separately. , which has the advantage of being resistant to noise caused by external electromagnetic fields.

A conventional structure of such an optical semiconductor device is known, for example, as described in Japanese Unexamined Patent Publication No. 1-205564. This is shown in FIG. In the same figure,
(1) is a P-type semiconductor substrate, (2) is a P-type epitaxial layer, (3) is an N-type epitaxial layer, and (4) is a P-type semiconductor substrate.
+ type isolation region, (5) is N+ type diffusion region, (6) is N+ type
Type buried layer, (7) is P type base region, (8) is N+
type emitter region. The photodiode (9) is formed by a PN junction between a P-type epitaxial layer (2) and an N-type epitaxial layer (3), with the N+ type diffusion region (5) taken out as a cathode and the isolation region (4) taken out as an anode. It is. The NPN transistor (10) has a buried layer (6) provided at the boundary between a P-type epitaxial layer (2) and an N-type epitaxial layer (3), and uses the N-type epitaxial layer (3) as a collector. An accelerating electric field is formed by the autodoped layer (11) from the substrate (1) to facilitate the movement of carriers generated in a region deeper than the depletion layer.

0004

However, from the viewpoint of high-speed response of the photodiode (9), it is desirable to widen the width of the depletion layer to suppress carriers generated outside the depletion layer. In the structure of FIG. 8, the autodoped layer (11) overlaps the P-type epitaxial layer (2), so the impurity concentration increases,
There was a drawback that it was difficult to expand the depletion layer.

Furthermore, when the P-type epitaxial layer (2) is laminated, the equipment becomes contaminated with acceptor impurities, so it must be separated from the equipment for growing the N-type epitaxial layer, and it cannot be used with other general bipolar ICs. The drawback was that it was difficult to share lines.

[0006]

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned drawbacks, and includes a first epitaxial layer (24) laminated in a non-doped manner on a substrate (23); ), an isolation region (26) completely penetrating the first and second epitaxial layers (24) (25), and a second epitaxial layer (25) stacked on top of the second epitaxial layer (25); The N+ type diffusion region (30) of the photodiode (21) formed on the surface of the photodiode (25), the N+ type buried layer (34) formed at the boundary between the first and second epitaxial layers (24) and (25), and the buried Layer (3
4) A high-speed photodiode (21) and an NPN transistor (22) formed on the surface of the second epitaxial layer (25) are provided.
22) is provided.

[0007]

[Operation] According to the present invention, the first epitaxial layer (2
4) and the second epitaxial layer (25), a photodiode (21) can be formed. Since the first epitaxial layer (24) is laminated without doping, the depletion layer can be expanded to be extremely thick by the thickness of the first epitaxial layer (24). Therefore, in addition to reducing the capacitance of the photodiode, the light absorption rate in the depletion layer can be increased and the generation of carriers generated outside the depletion layer can be suppressed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of an IC incorporating a photodiode (21) and an NPN transistor (22). In the same figure, (23) is a P-type single-crystal silicon semiconductor substrate, (24) is a first epitaxial layer with a thickness of 15 to 20 μm, which is laminated on the substrate (23) without doping by vapor phase epitaxy, (25) ) is the first epitaxial layer (24
) is a second epitaxial layer having a thickness of 4 to 6 μm and laminated with phosphorus (P) doping by vapor phase epitaxy. Substrate (2
3) uses a specific resistance of 40 to 60 Ω・cm, which has a lower impurity concentration than that of a general bipolar IC, and the first epitaxial layer (24) is laminated without doping, so that it has a resistivity of 1000 Ω・cm when laminated. The above results are 200 to 15
It has a specific resistance of 00Ω·cm. The second epitaxial layer (25) contains phosphorus (P) at a concentration of 1015 to 1016 cm-
By doping about 3%, it has a specific resistance of 0.5 to 3.0 Ω·cm.

[0010] The first and second epitaxial layers (24) (
25) is a P+ type isolation region (26) that completely penetrates both.
) electrically isolates the photodiode (21) forming portion and the NPN transistor (22) forming portion. This isolation region (26) includes a first isolation region (27) that is diffused in the vertical direction from the surface of the substrate (23), and a first isolation region (27) that is diffused in the vertical direction from the boundary between the first and second epitaxial layers (24) and (25). A third isolation region (28) formed from the surface of the second epitaxial layer (25)
9), and by connecting the three, the first and second epitaxial layers (24) and (25) are separated into islands.

[0011] On the surface of the second epitaxial layer (25) of the photodiode (21) portion, the photodiode (21)
An N+ type diffusion region (30) from which the cathode is taken out is formed on almost the entire surface. The surface of the second epitaxial layer (25) is covered with an oxide film (31), and a cathode electrode (32) is formed through a contact hole partially opened in the oxide film (31).
) contacts the N+ type diffusion region (30). Also,
The isolation region (26) is used as a low resistance extraction region on the anode side of the photodiode (21), and the anode electrode (33) contacts the surface of the isolation region (26).

At the boundary between the first and second epitaxial layers (24) and (25) of the NPN transistor (22),
An N+ type buried layer (34) is embedded. Second epitaxial layer (25) above buried layer (34)
A P-type base region (35), an N+-type emitter region (36), and an N+-type collector contact region (37) of the NPN transistor (22) are formed on the surface.

[0013] An Al electrode (38) is in contact with each diffusion region, and an Al wiring extending on the oxide film (31) connects each element, so that the photodiode (21) connects the optical signal input section. The NPN transistor (22) constitutes a signal processing circuit together with other elements.

Next, the function of the photodiode (21) will be explained.

The photodiode (21) applies a VCC potential such as +5V to the cathode electrode (32), and applies a VCC potential such as +5V to the anode electrode (32).
33) is operated in a reverse bias state where a GND potential is applied. When such a reverse bias is applied, the first and second epitaxial layers (24) (
The depletion layer spreads from the boundary of 25), and particularly spreads largely into the first epitaxial layer (24) because the first epitaxial layer (24) is a high resistivity layer. The depletion layer easily expands until it reaches the substrate (23) and has a thickness of 20~
An extremely thick depletion layer of 25μ can be obtained. Therefore, the junction capacitance of the photodiode (21) is reduced, enabling high-speed response.

Also in the present invention, the impurity (boron) in the substrate (23) is diffused into the first epitaxial layer (24) by heat treatment of each diffusion region to form a P-type autodoped layer. However, since the impurity concentration is superimposed on the non-doped layer, the impurity concentration does not become so high, and the substrate (
If a material with a relatively low impurity concentration of 40 to 60 Ω·cm is used as 23), this effect will be doubled. Therefore, the autodoped layer due to thermal diffusion does not inhibit the expansion of the depletion layer, and in this respect as well, a thick depletion layer can be obtained.

Furthermore, a first epitaxial layer (24)
When stacked without doping, during the epitaxial growth process, the epitaxial layer covers the substrate (23) and the first isolation region (23).
If boron (B) scattered from 27) recombines with silicon atoms and is deposited, or if unexpected impurities (mainly boron) enter from the outside, the layer can become a P-type layer that is very close to the intrinsic layer. However, since N-type inversion is unlikely to occur, by forming the N-type second epitaxial layer (25), P is suitable for forming a depletion layer.
An IN junction or a PN junction can be easily formed.

Furthermore, since a depletion layer thicker than the first epitaxial layer (24) is obtained, the absorption efficiency of incident light is high, and the carriers generated in the deep part of the photodiode (21) (outside the depletion layer) are correspondingly high. The ratio of generated carriers is also reduced, and the speed of the photodiode (21) can be increased.

Furthermore, carriers generated by light incidence reach the anode electrode (33) via the low-resistance separation region (26) on the anode side.
1) The series resistance can be reduced. Since the cathode side is recovered by the N+ type diffusion region (30) formed so as to cover the entire surface, the series resistance can be reduced.

The structure of FIG. 1 can be achieved by the following manufacturing method. First, the surface of the P-type substrate (23) is thermally oxidized to form an oxide film, and the oxide film is photo-etched to serve as a selection mask. Then, on the surface of the substrate (23) there is a separation region (
Boron (B) forming the first isolation region (27) of
) (Figure 2).

Next, after removing all the oxide film used as a selective mask, the substrate (23) is placed on a susceptor of an epitaxial growth apparatus, and the substrate (23) is heated by lamp heating.
) is heated to a high temperature of approximately 1140°C, and S is added to the reaction tube.
By introducing iH2Cl2 gas and H2 gas, the non-doped first epitaxial layer (24) is
Grow 0μ. When grown in this way without doping,
When all steps are completed, a high resistivity layer of 200 to 1500 Ω·cm can be formed (FIG. 3).

Next, the surface of the first epitaxial layer (24) is thermally oxidized to form a selective mask, and antimony forming the N+ type buried layer (34) of the NPN transistor (22) is diffused. With this heat treatment, the first separation region (27
) is also slightly diffused.

Next, the selection mask is changed and the separation region (2
6) Boron (B) forming the second isolation region (28)
spread. Then, while attaching an oxide film, the substrate (23
), the first and second separation regions (27) are subjected to heat treatment.
The two are connected by diffusing (28). In this step, the first isolation region (27) is diffused by 8 to 10μ, and the second isolation region (28) is diffused by 6 to 8μ. (FIG. 4) After that, the oxide film is removed and a phosphorus-doped second epitaxial layer (24) with a thickness of 4 to 6 μm is formed on the first epitaxial layer (24).
25) (Figure 5).

Next, the surface of the second epitaxial layer (25) is thermally oxidized to form a selective mask, and the isolation region (26) is
Boron (B) forming the third isolation region (29) is diffused and heat treated to form the second and third isolation region (28) (
29). In this step, the second separation region (28)
is 4 to 5 μ in the upward direction, and the third separation region (29) is 1 to 3
μ diffused (Figure 6).

Next, base diffusion is performed to form the base region (35) of the NPN transistor (22), and emitter diffusion is performed to form the emitter region (36) and collector contact region (37) of the NPN transistor (22).
and the N+ type diffusion region (30) of the photodiode (21).
) (Figure 7). Note that the third isolation region (29) can also be formed by the base diffusion described above.

Thereafter, the structure shown in FIG. 1 can be achieved by forming various electrode wirings by depositing Al and photo-etching.

[0027]

[Effects of the Invention] As explained above, according to the present invention,
Since the non-doped first epitaxial layer (24) is laminated, the depletion layer can be extended extremely thickly in the first epitaxial layer (24). Therefore, the junction capacitance can be reduced, the light absorption rate can be improved, and the generation of carriers generated outside the depletion layer can be suppressed, so there is an advantage that a photodiode (21) with an extremely fast response speed can be provided.

Furthermore, a high concentration low resistance isolation region (26)
reaches the substrate (23), so the series resistance of the photodiode (21) can be significantly reduced, and the isolation region (26) completely separates the photodiode (21) from the NPN transistor (22). Therefore, it has the advantage of preventing parasitic effects and the like.

Furthermore, by laminating the layers without doping, there is no need to control the impurity concentration, so it has the advantage that a high resistivity layer can be easily obtained, and the epitaxial growth apparatus is not contaminated with a large amount of boron (B). It has the advantage that the equipment is easy to maintain and the line can be shared with other models.

Furthermore, since the thick first epitaxial layer (24) is separated by the first and second isolation regions (27) and (28), the second isolation region (28) can be made shallower. However, lateral diffusion can also be reduced. Therefore, the second isolation region (28) and the N+ buried layer (34) can have a high breakdown voltage, which has the advantage of contributing to miniaturization of the NPN transistor (22).

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining an optical semiconductor device of the present invention.

FIG. 2 is a first drawing illustrating the manufacturing method of FIG. 1;

FIG. 3 is a second drawing illustrating the manufacturing method of FIG. 1;

FIG. 4 is a third drawing illustrating the manufacturing method of FIG. 1;

FIG. 5 is a fourth drawing illustrating the manufacturing method of FIG. 1;

FIG. 6 is a fifth drawing illustrating the manufacturing method of FIG. 1;

7 is a sixth drawing illustrating the manufacturing method of FIG. 1. FIG.

FIG. 8 is a sectional view showing a conventional example.

Claims (4)

[Claims] 1. A semiconductor substrate of one conductivity type, a first epitaxial layer laminated in a non-doped manner on the surface of the semiconductor substrate, and a second epitaxial layer of the opposite conductivity type formed on the surface of the first epitaxial layer. and the first and second
an isolation region of one conductivity type penetrating the epitaxial layer of the substrate to form the first and second epitaxial layers into a plurality of island regions; The first layer diffused halfway through the epitaxial layer.
forming a part of the separation region, and the first separation region forming a part of the separation region;
The second layer diffused vertically from the surface of the epitaxial layer.
forming a part of the separation region and the second separation region forming a part of the separation region;
a third isolation region diffused from the surface of the epitaxial layer to the middle of the second epitaxial layer, and one electrode of a photodiode in contact with the opposite conductivity type diffusion region formed on the surface of the first island region; the other electrode of the photodiode in contact with the surface of the separation region;
a buried layer of opposite conductivity type formed on the surface of the first epitaxial layer of the island region, and a base region of one conductivity type and an emitter region of opposite conductivity type formed on the surface of the second island region. An optical semiconductor device characterized by: 2. The semiconductor substrate has a specific resistance of 40 to 60.
2. The optical semiconductor device according to claim 1, wherein the resistance is Ω·cm. 3. The optical semiconductor device according to claim 1, wherein the first epitaxial layer has a specific resistance of 200 to 1500 Ω·cm. 4. The optical semiconductor device according to claim 1, wherein the opposite conductivity type diffusion region of the photodiode is formed simultaneously with the formation of the emitter region.