JPH01181560A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To improve the photosensitivity of a photodetector by a method wherein the conductivity type of the epitaxial layer of the photodetector region is turned into N-type by autodoping and the effective thickness of an N-type epitaxial layer is increased. CONSTITUTION:A second conductivity type (N-type) buried layer 8b is formed in the photodetector region of a first conductivity type (P-type) semiconductor substrate 1 beforehand and a first conductivity type epitaxial layer 7 is made to grow on the semiconductor substrate 1 and a second conductivity type portion 8c is formed in a part of the epitaxial layer 7 corresponding to the buried layer 8b by autodoping. Further, a second conductivity type epitaxial layer 2, is made to grow on the autodoped part to form a photodetector and another second conductivity type epitaxial layer 2' is made to grow on the other part of the first conductivity type epitaxial layer 7 which is not autodoped to form circuit elements. By taking structures like this, the effective thickness of the epitaxial layer 2' of the photodetector part can be increased. With this constitution, the sensitivity of a photodiode, which is the photodetector, can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor light receiving element in which a circuit element is formed together with the light receiving element.

(Prior art) With the development of laser discs, compact discs, etc., the use of light-receiving elements has increased, and instead of using light-receiving elements as a single unit, devices that are integrated with circuit elements for processing received signals are now available. is used. An example thereof is shown in FIG. In the figure, KN on the P-type semiconductor substrate 1 is shown.
A type epitaxial layer 2 is grown. Before growing the epitaxial layer 2, an N++ buried layer 5(a) is provided in the circuit element region of the semiconductor substrate l and an N''ffi buried layer 5(b) is provided in the light receiving element region. , these diffuse into the epitaxial layer 2, as shown in the figure.The buried layer 6 on the surface of the epitaxial layer 20
When a P+ type diffusion layer 3 is provided in a portion corresponding to (b), a photodiode is constituted by a PN junction between the two. Further, on the surface of the epitaxial layer 2, a base layer 4(a) consisting of a P+ type diffusion layer, N
By providing an emitter layer 4 (b) consisting of a + type scattering layer, a collector contact layer 4 (C) consisting of an N+ type scattering layer, etc., the transistor for processing the output signal of the photodiode is formed. configured. Between the photodiode and transistor regions, there is a P+ type isolation diffusion layer 6,
separated by 6°6.

(Problems to be Solved by the Invention) In such a device, in order to improve the sensitivity of the photodiode, which is a light receiving element, (1) the area of the PN junction used as the photodiode is increased;

(2) Increase the thickness of the epitaxial layer 2.

(3) Increase the specific resistance of the epitaxial layer 2.

This is necessary. However, in the cases of (1) and (2) above, the area, volume, etc. of the chip increases, leading to an increase in cost. In addition, in the case of (2) p (a), there is a problem that the accumulation time of minority carriers in the collector of a transistor serving as a circuit element and the collector series resistance increase, resulting in a slow response speed.

(Means for Solving the Problems) In the present invention, a buried layer of the second conductivity type is provided in advance in the region of the light receiving element of the semiconductor substrate of the first conductivity type, and a buried layer of the first conductivity type wtm is provided thereon. Growing an epitaxial layer, forming a second conductivity type part in a part corresponding to the buried layer by autodoping, and further growing a second conductivity type epitaxial layer on the autodoped part. A light-receiving element is formed, and a second conductivity type epitaxial layer is grown on the remaining non-autodoped epitaxial layer of the first conductivity type to form a circuit element.

(Function) With the structure as described above, the effective thickness of the epitaxial layer of the light receiving element portion can be increased. The optimum epitaxial layer thickness can be set for the circuit element section separately from the light receiving element section.

(Example) An example of the present invention is shown in FIGS. 1<8), (b), and (c).

First, as shown in FIG. 1(a), an N+ type buried layer 8(b) is formed in the light-receiving element region of the P-type semiconductor substrate 1 by photolithography and impurity diffusion.

Next, as shown in FIG. 1(b), a P-type lower epitaxial layer 7 is grown, and the lower epitaxial layer 7 on the N+fi+ buried layer 8(b) is replaced by the N medium-type buried layer 8(b). Using an auto-doping trap, heat treatment is applied to transform the layer into 8 layers (8(c)). This heat treatment, including the heat treatment in subsequent steps, is performed under conditions such that the lower epitaxial layer 7 corresponding to the buried layer 5 (b) changes into 8 layers 13 (c) as a whole. Can be set. By changing the heat treatment conditions, autodoping of the N medium-sized buried layer 8(b) in the light receiving element region can be controlled, so the growth conditions for the lower epitaxial layer 7 can be set arbitrarily. Thereafter, a P-shaped buried layer 9 is formed to separate the light receiving element and the circuit element. It is also possible to form a separation diffusion layer in a later step without providing this buried layer 9.

Furthermore, as shown in FIG. 1(c) VC, in the region of the circuit element on the left side of the figure, in the lower epitaxial layer 7,
The N medium-sized buried layer 8(a) is formed by the same method as the N medium-sized buried layer 8(b). An N-type upper epitaxial layer 2' is grown thereon, and by photo-raffy, impurity diffusion, etc., an N+-type scattering layer 10 for taking out the photodiode electrode and a P layer for the photodiode are formed in the light-receiving element region.
A P+ type diffusion layer 8' is formed to form an N junction,
Circuit element area - C, door-shaped diffused layer 4 which becomes the base of the signal processing transistor ta)'t N+ type scattered layer 4b)' which becomes the emitter and N+ type scattered layer 4c)' which becomes the collector contact. Form. Further, at the boundary between the light receiving element and the circuit element, a P+ type diffusion layer 11.1 for separating the negative element is provided.
Set 1□.

(Effects of the Invention) With the above structure, the epitaxial layer below the light receiving element region is changed to N type by autodoping, so the effective thickness of the N type epitaxial layer is increased. Therefore, the minority carriers generated by light in the lower epitaxial layer also become particles contributing to the photocurrent of the photodiode, and the photosensitivity of the light receiving element can be improved without increasing the chip area.

Furthermore, epitaxial conditions for the circuit element that can achieve a desired response speed can be set independently of the light receiving element.

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

Photosensitivity is indicated by the amount of light absorption that contributes to the photocurrent of the photodiode. The light used is a commonly used semiconductor laser light with a wavelength of 760 nm.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) show a schematic cross-sectional view of the process and finished product of an embodiment of the present invention, and FIG. 2 shows a schematic cross-sectional view of a conventional example. ! ...Semiconductor substrate 2'...N type epitaxial layer 8'...P+ diffusion layer 7...P type epitaxial layer 8(a)...N++ buried layer 8(b)...N
++ Embedded layer 8 (C)...8 layers 9...P-type embedded layer 10...N+-type scattered layer 11...P+-type separated greedy layer Patent applicant Sharp Corporation Agent Patent Attorney Aihiko Fukushi

Claims (1)

[Claims] (1) a semiconductor substrate of a first conductivity type in which a buried layer of a second conductivity type is provided in a region of a light receiving element; an epitaxial layer of a first conductivity type formed on the semiconductor substrate; A part of the epitaxial layer is of a second conductivity type formed by autodoping the buried layer of the second conductive dust, and a part of the second conductivity type which has been autodoped is formed on a part of the epitaxial layer. A semiconductor light-receiving element in which a light-receiving element is formed and a circuit element is formed on the remaining portion of an epitaxial layer of a first conductivity type that is not auto-doped.