JPS60178673A - avalanche photodiode - Google Patents

Abstract

PURPOSE:To enable the APD having a uniform multiplying region to be obtained by a method wherein the impurity concentration at the center of the first conductivity type region of high concentration is made higher than that in the periphery of this first conductivity type region. CONSTITUTION:The breakdown voltage of both the center of the high concentration region and its periphery is made to have a difference by having a difference in impurity concentration. This difference in withstand voltage can be arbitrary taken according to states of formation of said high concentration region. The method of forming the high concentration region includes: (1) formation by ion implantation after a recess is bored in the substrate by etching, and by heat treatment thereafter and surface etching; (2) formation by setting the injection dosage at a desired value by variation in thickness of a selective injection mask, and thereafter by heat treatment; (3) formation by many times of selective ion implantation and heat treatment thereafter. Then, a P<+> region is formed, and a guard ring is formed if not formed into an element structure. Thus, a distribution of impurity concentration where there is some difference in impurity concentration between the center and the periphery in the region 18, leading to uniform multiplication is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to the structure of a half-balance receiving element, and particularly to an avalanche photodiode (hereinafter abbreviated as APD).

(Prior art and its problems) API) Various materials such as 4-8i, Ge, and compound semiconductors are used. Here, to make the discussion easier to understand, Ge
This will be explained using an example.

Germanium is an avalanche photodiode (AP)
The depletion layer width near the junction has a great influence on the performance of the device.

Germanium APDs, which are light-receiving elements for optical fiber tracking systems, have already been put into practical use in the 1.3 μm band, but there is an urgent need to develop light-receiving elements for the 1.5 μm band, which is the minimum loss region of optical fibers. There is. In order to have good sensitivity to light in the wavelength band of 1.5 μm, it depends on how the width of the depletion layer is expanded.

It is known that the light absorption coefficient of germanium is approximately 7×10/α for light with a wavelength of 1.55 μm. Therefore, the original absorption length needs to be 15 μm or more, and when the depletion layer 1- is less than 5 μm, the light absorption deep within the substrate deeper than the edge of the depletion layer becomes a slow diffusion component and a flow component, which causes deterioration of the photoresponse characteristics. It becomes a factor. In order to improve the frequency characteristics as described above, it is necessary to set the width of the S depletion layer to 15 μm or more so that the incident light is sufficiently absorbed within the depletion layer. The same can be said for other materials.

FIG. 1 is a structural diagram of a well-known so-called Brehner type APDO in which a pn junction serving as a light-receiving surface is manufactured by a boron ion implantation process and a heat treatment process.

In 1a, a P region 12 of +0.3 μm n radius is formed on an n-type germanium substrate 11 as a light receiving region. In the figure, 13 is the insulation 1@, 14, and 15 are the p1IIll electrode and the n1lil electrode, respectively.
6 is a guard ring consisting of a low medical grade area. A device having this structure is used by applying a reverse voltage #:IJ to the pn junction formed between Rj and 11.12 through electrodes 14 and 15. With this willow sac API), there is a limit to the expansion of the depletion layer width, so good sensitivity is only 1-0-' at most.
With this structure, it is difficult to obtain a depletion layer width of 15 μm or more, which is necessary to have high sensitivity to light in the 1.5 μm band on the longer wavelength side.

This is due to the following. When considering the step junction approximation to the pn junction, in order to make the depletion layer width 15 μm or more, the n-type substrate concentration must be 3XlO/i or less, and the breakdown voltage at that time will be 300V or more. With such a low concentration substrate, it is difficult to obtain a breakdown voltage difference from the breakdown voltage of the guard ring, and uniform multiplication within the photodetector tube cannot be obtained. In addition, if the reverse applied voltage is required to be 300 V or more, operation at a resistive voltage is required, which is practical in a system that requires 1C to occur.

In order to overcome the above problem, a so-called high-low (H1-Lo) structure shown in FIG. A light receiving element is made. In the figure, reference numeral 17 indicates a region with relatively high impurity concentration (hereinafter referred to as a high concentration region). In this structure, electric field strength sufficient to cause T-balance breakdown can be obtained in the vicinity of the pn junction 6 formed between 12 and 17 in the figure, and the low concentration substrate (1 in the figure
1), a high-speed response and a depletion layer width can be obtained with a low IEIJ applied voltage.

In this structure, since the high concentration region becomes the light receiving portion, the impurity concentration distribution must be uniform within the plane. This is due to the following. If the impurity concentration distribution is non-uniform in the plane, when a reverse voltage is applied to this element, the electric field will be concentrated in the lagoon region, and for example, as shown in Figure 3, the multiplication line scan will be sharp. become. Since the effective light-receiving area of a device with uneven multiplication becomes small, during actual operation, it is necessary to set the multiplication factor at the peak of the multiplication to a somewhat higher value than the optimum multiplication factor of the APD. be.

At this time, of course, the signal-to-noise ratio is not very good. As a result of the following, the impurity zone 4 is reduced in the high concentration region.
The degree 45 must be uniform across the plane i, but
In the current E structure, the electric field is generally concentrated in the middle/U part of the high concentration region, making it difficult to obtain uniform multiplication. This seems to be due to the substantially in-plane non-uniform impurity concentration distribution due to surface treatment etc. in the element manufacturing process after the manufacturing process.

(Objective of the Invention) The present invention overcomes the drawbacks of the above-mentioned conventional methods and provides an APD structure having a uniform multiplication region.

(Structure of the Invention) The present invention provides a first conductive type resistor semiconductor having a second conductive type region in the vicinity of the surface thereof, and a second conductive type region in the first conductive type high resistive semiconductor and the second conductive type region in the first conductive type high resistance semiconductor layer. In an avalanche photodiode including a high concentration wJl conductivity type region provided adjacent to a portion of the second conductivity type region that becomes a light receiving region, the impurity concentration in the central part of the high concentration 14th type region is The feature is that the impurity concentration is higher than the impurity concentration in the peripheral portion of the high concentration first conductivity type region.

(Operations and Effects of the Invention) The structure of the present invention will be described below by taking an n-type germanium substrate as an example. #! FIG. 4(a) shows an n-type high concentration region formed by selective ion implantation and subsequent heat treatment. In this structure, in the high concentration region, there is a difference in impurity concentration between the central part and the peripheral part, so that there is a difference in breakdown voltage between the two regions. This difference in breakdown voltage can be set arbitrarily depending on the state of formation of the high concentration region. The method for forming the high concentration region is as follows: ■ Substrate (H in the figure)
A method in which the four parts are formed by etching on top, followed by ion implantation, followed by heat treatment and surface etching.

■ A method in which the implantation dose is adjusted to a desired value by changing the thickness of the mask, and then heat treatment is performed. o There is a method of forming by selective ion implantation multiple times and subsequent heat treatment. When forming the high concentration region using any of the above methods, it does not matter whether the guard ring (16 in the figure) has already been formed or not. Thereafter, a P region is formed, and if a guard ring is not formed, a guard ring is formed to obtain the device structure shown in FIG. 4(b). In the structure of the present invention, there is a slight difference in impurity concentration between the center and the periphery in region 8, forming an impurity concentration difference distribution that provides uniform multiplication.

(Example) Examples of the present invention will be described in detail. In the structure shown in Fig. 4(b), an n-type germanium substrate (11 in the figure) with a net impurity concentration of 5 x 1.0 /- is formed by a guard ring (16 in the figure) by the zinc thermal diffusion method at 650°C for 16 hours. After formation 3, arsenic ion implantation (dose 1.20/-,
ion acceleration energy = 130 keV) and subsequent 66
High concentration region 18 is formed by activation annealing at 7° C. for 8 hours (8i02 film, in hydrogen atmosphere) and surface etching. After that, boron ion implantation (dose control = 3
xto /cJ, ion acceleration energy = 49 k
ey) and subsequent activation annealing at 650°C (Sin, protective film, hydrogen atmosphere) to form the P region 12 into the shape M,
Tru. As a surface protective film, 8i0. Attach a film (13 in the figure), p111t4 & (14 in the figure) toshite aluminum (AJ), n1lllljt [(15 in the figure)
Then, gold-germanium (Au-Ge) is deposited. FIG. 5 shows a line scan of the multiplication of the germanium APD manufactured according to this example.

The measurement was performed using a laser beam with a wavelength of 1.55 μm, and uniform multiplication was obtained within the light receiving surface. The breakdown voltage of the device according to this example was 90 V, and this is because the electric field strength at the pn junction in the peripheral area of the light receiving portion reached the breakdown electric field strength. In fact, the difference in breakdown voltage between the central part and the peripheral part of the light receiving part is thought to be about 5V.

Although germanium was used in the above embodiments, it goes without saying that other semiconductor materials such as gallium arsenide and gallium antimony threads may be used.

[Brief explanation of the drawing]

Figure 1 shows a conventionally known APD made of pn II.
o) Cross-sectional view. FIG. 2 is a cross-sectional view of an API (API) having a region with relatively high impurity concentration. Figure 3 shows the AP with the structure shown in Figure 2.
T diagram showing the multiplication line scan obtained in D. Figure 4 (
Figure a) is a cross-sectional view of the main steps of manufacturing the APD of the present invention, and Figure (b) is a cross-sectional view of the APD of the present invention. FIG. 5 is a diagram showing a multiplication line scan obtained by the APD of the present invention. 11 n germanium substrate 12 high concentration p region 13 surface protective film 14 pull pole 15 n

Claims (1)

[Claims] At least the second conductivity type is located near the surface of the high-low resistance semiconductor layer of the first conductivity type.
A high-concentration semiconductor layer is provided in the first conductivity type high-resistance semiconductor layer and adjacent to the light-receiving area of the former Mf second conductivity type region. In the avalanche photodiode having a 14th conductivity type region, the impurity concentration in the central part of the high concentration first conductivity type region is higher than the impurity concentration in the peripheral part of the high concentration first conductivity type region. Avalanche photodiode with a low value of 41 (!:T).