JPH01181559A - Photodetector with built-in circuit - Google Patents

Abstract

PURPOSE:To improve the photosensitivity of a photodetector part by a method wherein the thickness of the epitaxial layer of a photodetector region is larger than the thickness of the epitaxial layer of a circuit element region. CONSTITUTION:A recess 10 is formed in the photodetector region of a first conductivity type semiconductor substrate 11 by anisotropic etching and second conductivity type diffused layers 12, 12 and 12 are formed on the inner wall surface and circuit element regions of the recess 10. Then a second conductivity type epitaxial layer 13 is made to grow on the surface of the substrate 11 and the surface is polished and levelled. The thickness of the epitaxial layer of the photodetector region is larger than that of the epitaxial layer of the circuit element region. The photodetector is composed of a center part first conductivity type diffused layer 16 and the second conductivity type epitaxial layer 13 and transistors are composed of second conductivity type diffused layers 17 and 17, the epitaxial layers 13 and 13 and first conductivity type diffused layers 16 and 16 of the both sides to provide the circuit element. With this constitution, the photosensitivity of the photodetector region can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light receiving element with a built-in circuit, in which a circuit element and a light receiving element are provided on the same substrate, and the light sensitivity of the light receiving element is increased.

(Prior art) With the spread of devices that use light, light-receiving elements with a built-in circuit have been developed, in which a light-receiving element for picking up signals and a circuit element for processing signals from the light-receiving element are formed on the same substrate. ,
It is becoming widely used.

In such devices, the light-receiving element is required to have high photosensitivity, the circuit element is required to have high speed and good frequency characteristics, and on top of both, low manufacturing costs are required. requested. An example of a conventional light-receiving element with a built-in circuit is shown in FIG. A buried diffusion layer 2, 2.2 of the second conductivity type is formed in the light receiving element region and the circuit element region of the semiconductor substrate l of the first conductivity type, and an epitaxial layer of the second conductivity type is formed thereon. Grow layer 8. Second lead 1
When the Jt type buried diffusion layer 2 is n+, the second conductive epitaxial layer 8 is n. At this time, the surface of the buried diffusion layers 2, 2, 2 of the second conductivity type is initially the same as the surface of the semiconductor substrate 10 of the first conductivity type, but the surface of the second conductivity type epitaxial layer 30 is then 1 conductivity type separation diffusion layer 4
, 4.4 are formed at the boundary between the light receiving element region and the circuit element region, and the second conductive diffusion layer 5, 5.5 is formed from the surface to the second conductive type buried diffusion layer 2, 2.4. Form up to 2.

Further, first conductivity type diffusion layers 6, 6.6 are formed.

The center portion of FIG. 2 is the region of the light receiving element, and the light receiving element is formed by the diffusion layer 6 of the first conductivity type and the epitaxial layer 8 of the second conductivity type. The parts on both sides of FIG. 2 are circuit element regions, and the first conductivity type diffusion layers 6,
Diffusion layers 7, 7 of a second conductivity type are further formed in 6. The epitaxial layer 8 and diffusion layer 7 of the second conductivity type and the diffusion layer 6 of the first conductivity type constitute a transistor.

(Problems to be Solved by the Invention) In order to increase the sensitivity of the light receiving element, it is preferable to make the epitaxial layer thicker. However, when the epitaxial layer is made thicker, the high-speed performance of the circuit element is lost, the chip size becomes larger, and the cost increases. When the epitaxial layer is made thinner in order to increase the speed and reduce the chip size of the circuit element, there is a problem in that the photosensitivity of the light-receiving element decreases.

(Means for solving the problem) In the conventional structure shown in FIG. 2, the thickness of the epitaxial layer 3 in both the light-receiving element region and the circuit element region was between the two. In the invention, the thickness of the epitaxial layer in the region of the light receiving element is made thicker than the thickness of the epitaxial layer in the region of the circuit element.

(Function) According to the present invention, the above-mentioned problems can be solved, the photosensitivity of the light-receiving element section can be increased, and the high-speed performance or frequency characteristics of the circuit element section can be improved.

(Example) Figures 1 (a), (b), (c) and (d) are
1 is a cross-sectional view of a manufacturing process and a finished product of a light-receiving element with a built-in circuit according to the present invention.

As shown in FIG. 1), first, a recess 10 is formed in the light receiving element area of the first conductivity type semiconductor substrate 11 by anisotropic etching, and a recess 10 is formed on the inner wall surface of the recess 10 and in the circuit element area. 2 conductivity type diffusion layers 12.12.12 are formed. This second conductivity type diffusion layer 12 functions to lower the series resistance of the light receiving element.

Next, as shown in FIG. 1(b), an epitaxial layer 18 of a second conductivity type is grown on the surface of the semiconductor substrate 110 of the first conductivity type. The specific resistance of the epitaxial layer is the optimum value for both the circuit element and the light receiving element, for example, 1Ω steel, and the surface is then polished to make it flat to the extent that it does not interfere with subsequent steps. This state is shown in FIG. 1(c). At this time, the thickness of the epitaxial layer is, for example, 6 μm at the thickest part in the light receiving element region and 3 μm in one circuit element region.

The optimum thickness is selected depending on the purpose of use.

Furthermore, as shown in FIG. 1(d), first conductivity type diffusion layers 14, 14, 14.14 for element isolation are formed, and buried layers 12.12 of gg2 conductivity type are formed from the surface. Diffusion layers 15 , 15° 16 of the second conductivity type up to .12 are formed, and then diffusion layers 16 , 16 .
16, and first conductivity type diffusion layers 16, 16 at both ends.
A second conductivity type diffusion layer 17.17 is formed in a part of the semiconductor device. A light-receiving element is constituted by a first conductivity type diffusion layer 16 and a second conductivity type epitaxial layer 18 in the center of the figure, and second conductivity type diffusion layers 17.17 and epitaxial layers 18.18 on both sides. and a first conductivity type diffusion layer 16.16
Each of these constitutes a transistor and becomes a circuit element. First conductivity type separation diffusion layer 14, 14...The subsequent steps are the same as the conventional one.

(Effects of the Invention) According to the present invention, an epitaxial layer that satisfies the optimum epitaxial layer conditions for the circuit element region (for example, resistivity 10G, thickness 8 μm) and increases the photosensitivity of the light receiving element region. The conditions (for example, specific resistance of 1Ω, thickness of 8 μm) can be satisfied.

A comparison between an example of the conventional example and an example of the present invention is shown in the table below.

(Hereinafter referred to as margin) Photosensitivity can be expressed by the amount of original absorption that contributes to the photodiode photocurrent of the light receiving element. The original wavelength used for comparison was 760 nm of commonly used semiconductor laser light.
It is nm. As shown in the table above, it can be seen that according to the present invention, the photosensitivity can be approximately doubled compared to the conventional method.

Additionally, depending on the purpose of use, the thickness of the epitaxial layer in the circuit element area and the photodetector area can be independently set to the optimal conditions, making it possible to produce a photodetector with a built-in circuit at a low cost and with high photosensitivity and good frequency characteristics. Can be manufactured.

[Brief explanation of the drawing]

1(a) p(b)*(C) and (d) show the process of forming a light receiving element with a built-in circuit according to the present invention and a cross section of a completed product. The vJz diagram shows a cross section of a conventional photodetector with a built-in circuit. 11... Semiconductor substrate of first conductivity type 12... Buried diffusion layer 18 of second conductivity type... Epitaxial layer 14 of second conductivity type...
Separation diffusion layer 15 of first conductivity type...Diffusion layer 16 of second conductivity type...Diffusion layer 17 of wjl conductivity type...Diffusion layer of second conductivity type Patent applicant Sharp Corporation -1X agent patent attorney Yoshihiko Fukushi! 11.・Filling l Figure tσノAtsushi 1511 (C) @/ Figure (d) Filling 2 Figure

Claims (1)

[Claims] (1) A light-receiving element with a built-in circuit, comprising a circuit element and a light-receiving element, and characterized in that the epitaxial layer in the region of the light-receiving element is thicker than the thickness of the epitaxial layer in the region of the circuit element.