JP2940818B2 - Optical semiconductor device and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical semiconductor device in which a photodiode and a bipolar IC are integrated.

[0002]

2. Description of the Related Art An optical semiconductor device in which a light receiving element and a peripheral circuit are integrated and formed in a monolithic manner is different from a hybrid IC in which a light receiving element and a circuit element are separately manufactured, and cost reduction can be expected. It has the advantage of being strong against noise due to external electromagnetic fields.

[0003] As a conventional structure of such an optical semiconductor device, for example, one described in Japanese Patent Application Laid-Open No. 1-205564 is known. This is shown in FIG. In the 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 epitaxial layer.
A + type isolation region, (5) an N + type diffusion region, (6) an N + type buried layer, (7) a P type base region, and (8) an N + type emitter region. The photodiode (9) is formed by a PN junction of the P-type epitaxial layer (2) and the N-type epitaxial layer (3), and the N + type diffusion region (5) is taken as a cathode and the isolation region (4) is taken as an anode. Things. The NPN transistor (10) has a buried layer (6) provided at the boundary between the P-type epitaxial layer (2) and the N-type epitaxial layer (3), and uses the N-type epitaxial layer (3) as a collector. Then, an acceleration electric field is formed by the auto-doped layer (11) from the substrate (1), thereby facilitating the movement of carriers generated in a region deeper than the depletion layer.

[0004]

However, in terms of the high-speed response of the photodiode (9), it is desirable to increase the width of the depletion layer to suppress carriers generated outside the depletion layer.
In the structure of FIG. 8, since the auto-doped layer (11) is superimposed on the P-type epitaxial layer (2), the impurity concentration increases,
There is a disadvantage that it is difficult to enlarge the depletion layer.

When the P-type epitaxial layer (2) is stacked, the device is contaminated with acceptor impurities. Therefore, the device must be separated from the device for growing the N-type epitaxial layer. There was a disadvantage that it was difficult to share the line.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and comprises a first epitaxial layer (24) non-doped on a substrate (23) and a first epitaxial layer (24). A) an N-type second epitaxial layer (25) laminated thereon and an isolation region (26) completely penetrating the first and second epitaxial layers (24) and (25).
An N + -type diffusion region (30) of a photodiode (21) formed on the surface of the second epitaxial layer (25);
An N + -type buried layer (34) formed at the boundary between the first and second epitaxial layers (24) and (25), and an NPN transistor formed on the surface of the second epitaxial layer (25) on the buried layer (34) By providing (22), an optical semiconductor device in which the high-speed photodiode (21) and the NPN transistor (22) are integrated is provided.

According to the present invention, the photodiode (21) can be formed by joining the first epitaxial layer (24) and the second epitaxial layer (25). Since the first epitaxial layer (24) was laminated without doping,
The depletion layer can be extremely thickened by the thickness of the first epitaxial layer (24). Therefore, the capacity of the photodiode can be reduced, 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]

DETAILED 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 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 having a thickness of 15 to 20 μ and non-doped on the substrate (23) by a vapor phase growth method, (25) ) Is the first epitaxial layer (2
4) A second epitaxial layer having a thickness of 4 to 6 μm, which is stacked on the substrate by phosphorus (P) doping by a vapor phase growth method. The substrate (23) has 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 non-doped so as to be 1000 Ω at the time of lamination. · 200 cm or more at the time of completion after heat treatment for forming a diffusion region
It has a specific resistance of 1500 Ω · cm. The second epitaxial layer (25) is doped with phosphorus (P) by about 10 15 to 10 16 cm -3 to form 0.5 to 3.0.
It has a specific resistance of Ω · cm.

First and second epitaxial layers (24)
(25) is a P + type isolation region (2
6) the photodiode (21) forming portion and the NPN
It is electrically separated from the transistor (22) formation portion. The isolation region (26) is vertically diffused from the surface of the substrate (23) in the vertical direction from the first isolation region (27) diffused in the vertical direction from the surface of the substrate (23), and from the boundary between the first and second epitaxial layers (24) and (25). And a third isolation region (29) formed from the surface of the second epitaxial layer (25). The first and second epitaxial layers ( 24) Separate (25) into islands.

On the surface of the second epitaxial layer (25) in the photodiode (21) portion, a photodiode (21)
An N + type diffusion region (30) for taking out the cathode is formed on substantially the entire surface. The surface of the second epitaxial layer (25) is covered with an oxide film (31), and the cathode electrode (3) is formed through a contact hole partially opened in the oxide film (31).
2) contacts the N + type diffusion region (30). Further, the isolation region (26) is used as an anode-side low-resistance extraction region 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 buried. Second epitaxial layer (25) above buried layer (34)
On the surface, 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.

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

Next, the operation of the photodiode (21) will be described.

The photodiode (21) applies a VCC potential such as +5 V to the cathode electrode (32) and the anode electrode (3).
3) The device is operated in a reverse bias state in which a GND potential is applied. When such a reverse bias is applied, the first and second epitaxial layers (24) (2) of the photodiode (21) are
The depletion layer extends from the boundary of 5), and particularly greatly expands in the first epitaxial layer (24) since the first epitaxial layer (24) is a high resistivity layer. The depletion layer easily spreads to the substrate (23) and has a thickness of 20 to 2 mm.
An extremely thick depletion layer of 5 μ can be obtained. Therefore, the junction capacitance of the photodiode (21) is reduced, and high-speed response is enabled.

In the present invention, the impurity (boron) in the substrate (23) is diffused into the first epitaxial layer (24) by the heat treatment of each diffusion region to form a P-type auto-doped layer. However, since the impurity concentration is not so high because it is superimposed on the non-doped layer, the effect is doubled when a substrate (23) having a relatively low impurity concentration of 40 to 60 Ω · cm is used. for that reason,
The auto-doped layer by thermal diffusion does not inhibit the expansion of the depletion layer, and a thick depletion layer can be obtained also in this regard.

Further, a first epitaxial layer (24)
Is deposited non-doped, during the epitaxial growth step, the epitaxial layer is formed by the boron (B) scattered from the substrate (23) or the first isolation region (27) being recombined with silicon atoms and deposited, or from the outside. A non-impurity (mainly boron) intrusion can result in a P-type layer very close to the intrinsic layer. However, since N-type inversion is unlikely, it is possible to easily form a PIN junction or a PN junction suitable for forming a depletion layer by forming the N-type second epitaxial layer (25).

Further, since a thick depletion layer having a thickness equal to or greater than the thickness of the first epitaxial layer (24) is obtained, the efficiency of absorption of incident light is high, and the carriers generated in the deep portion of the photodiode (21) by that amount (outside the depletion layer). The ratio of generated carriers is also reduced, and the speed of the photodiode (21) can be increased.

The carriers generated by light incidence reach the anode electrode (33) via the low-resistance separation region (26) on the anode side, so that the series resistance of the photodiode (21) 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 shown in 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 form a selection mask. Then, boron (B) forming the first isolation region (27) of the isolation region (26) is diffused on the surface of the substrate (23) (FIG. 2).

Next, after removing all the oxide film used as the selection mask, the substrate (23) is placed on the susceptor of the epitaxial growth apparatus, and the substrate (2) is heated by a lamp.
By applying a high temperature of about 1140 ° C. to 3) and introducing SiH 2 Cl 2 gas and H 2 gas into the reaction tube, the non-doped first epitaxial layer (24) is
Grow 0μ. When grown non-doped in this way,
Upon completion of the entire process, 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 selection mask, and antimony forming the N + type buried layer (34) of the NPN transistor (22) is diffused. By this heat treatment, the first separation region (2
7) is also diffused a little.

Next, the selection mask is changed and the separation region (2
Boron (B) forming the second isolation region (28) of 6)
To spread. Then, the substrate (2)
3) A heat treatment is applied to the whole, and the first and second separation regions (2
7) Connect both by diffusing (28). In this step, the first separation region (27) is diffused by 8 to 10 μm, and the second separation region (28) is diffused by 6 to 8 μm. (FIG. 4) Thereafter, the oxide film is removed to form a first epitaxial layer (24).
Then, a phosphorus-doped second epitaxial layer (25) having a thickness of 4 to 6 μm is formed thereon (FIG. 5).

Next, the surface of the second epitaxial layer (25) is thermally oxidized to form a selective mask, and the isolation region (26) is formed.
The boron (B) forming the third isolation region (29) is diffused, and heat treatment is applied to the second and third isolation regions (28).
(29) is connected. In this step, the second separation region (2
8) is 4-5 μ upward, and the third separation region (29) is 1 μm.
３3μ is diffused (FIG. 6).

Next, base diffusion is performed to form a base region (35) of the NPN transistor (22), and emitter diffusion is further performed to diffuse the emitter region (36) and the collector contact region (37) of the NPN transistor (22).
And the N + type diffusion region (3
0) is formed (FIG. 7). Incidentally, the third separation region (29)
Can be formed by the base diffusion described above.

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

[0027]

As described above, according to the present invention,
Since the non-doped first epitaxial layer (24) is laminated, the depletion layer can be extremely thickly spread in the first epitaxial layer (24). Therefore, it is possible to provide a photodiode (21) having a very high response speed since 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.

Further, a high-concentration low-resistance isolation region (26)
Reaches the substrate (23), 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, there is an advantage that a parasitic effect or the like can be prevented.

Furthermore, by stacking non-doped layers, it is not necessary to control the impurity concentration, so that a high resistivity layer can be easily obtained. In addition, the epitaxial growth apparatus is not contaminated with a large amount of boron (B). It has the advantages that the maintenance of the device is easy and the line can be shared with other models.

Further, since the first epitaxial layer (24) having a large thickness is separated by the first and second separation regions (27) and (28), the second separation region (28) can be made shallower and the second separation region (28) can be made shallower. Only lateral diffusion is reduced. Therefore, the withstand voltage between the second isolation region (28) and the N + buried layer (34) can be increased, which has the advantage that it can contribute to miniaturization of the NPN transistor (22).

[Brief description of the drawings]

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

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

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

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 31/10 H01L 27/06 H01L 27/14

Claims (3)

(57) [Claims] 1. A semiconductor substrate of one conductivity type, a first epitaxial layer non-doped on the surface of the semiconductor substrate, and a second epitaxial layer of opposite conductivity type formed on the surface of the first epitaxial layer Through the first and second epitaxial layers, the first
Forming a part of the isolation region, forming a part of the isolation region, and vertically diffusing from the surface of the substrate; A first isolation region diffused partway through the epitaxial layer, a second isolation region forming a part of the isolation region, and vertically diffusing from the surface of the first epitaxial layer; A third isolation region partially formed and diffused from the surface of the second epitaxial layer to the middle of the second epitaxial layer; and a diffusion region of the opposite conductivity type formed on the surface of the first island region. One electrode of a photodiode in contact with the other, the other electrode of the photodiode in contact with the surface of the isolation region, and a reverse conductivity type buried formed on the surface of the first epitaxial layer in a second island region If, comprising a second island region of one conductivity type formed on the surface of the base region and the opposite conductivity type emitter region, the semiconductor substrate is the first, the second and third separation region
Electrically connected to the other electrode of the photodiode via
The optical semiconductor device characterized by being. 2. The optical semiconductor device according to claim 1, wherein the first epitaxial layer has a specific resistance of 200 to 1500 Ω · cm. 3. a step of preparing a semiconductor substrate of one conductivity type; a step of selectively diffusing impurities of one conductivity type on a surface of the semiconductor substrate to form a first isolation region; Forming a first epitaxial layer on the semiconductor substrate in a substantially non-doped state; forming a second isolation region of one conductivity type on the surface of the first epitaxial layer; A step of forming a second epitaxial layer on the first epitaxial layer by doping an impurity of the opposite conductivity type, and a second separation of one conductivity type on the surface of the first epitaxial layer. Forming a region, forming a third isolation region of one conductivity type on the surface of the first epitaxial layer, and connecting the first, second, and third isolation regions to form the first and second isolation regions. 2 of the first and second epitaxial layers Separating the island into island regions; forming a base region of one conductivity type on the surface of the second island region; forming an emitter region of the opposite conductivity type on the surface of the base region; Forming a diffusion region of a reverse conductivity type in the region, and one electrode of a photodiode on the surface of the isolation region,
Forming the other electrode of the photodiode on the surface of the diffusion region of the opposite conductivity type, wherein the semiconductor substrate forms the first, second and third isolation regions.
Electrically connected to the other electrode of the photodiode via
A method for manufacturing an optical semiconductor device, comprising: