JPH0582827A - Semiconductor light receiving element - Google Patents

Abstract

PURPOSE:To lessen the parasitic capacity and improve the high-speed responsiveness by having a passivation-cum-reflection preventive film on the surface of an element, and specifying the thickness. CONSTITUTION:The crystals of n<+>-InP 2, n<->-InGaAs 3, and n-InP layers 4 are stacked in order on a semiinsulating InP substrate 1, and then pn junction is made in the InGaAs 3 by the selective heat diffusion of Zn. Next, a mesa 6 including a light receiving part and a mesa 7 for an electrode are made by selective etching, and then a silicon nitride film 8 is made on the surface of the element by plasma CVD. This film doubles as a passivation film and a reflection preventive film, and the thickness shall be the wavelength (2n+1) within the film of an incident light/4 times (n is a natural number). Thereby, the process for changing the thicknesses of the films on the light receiving part and the section excluding it can be omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element.

[0002]

2. Description of the Related Art A semiconductor light receiving element using a compound semiconductor is widely used as an element for optical communication. An example of this optical communication element is an InGaAs pin photodiode. Higher response characteristics and improved receiver sensitivity are required for this device. It is important to reduce the element capacitance in order to speed up the response characteristics. For that purpose, it is necessary to reduce the junction diameter sufficiently to reduce the junction capacitance and also the parasitic capacitance. As an element structure for reducing the parasitic capacitance, for example, p ₊ by selective diffusion is used _.
-In the case of an n-type planar type element, a p-electrode is formed in a mesa-isolated region different from the light-receiving part by using an element isolation technique using a semi-insulating substrate and a mesa structure, and a step is formed between this and the p ⁺ region. A structure in which wiring is used for connection is being considered. By adopting such a structure, it is possible to form a p-pad electrode having a large area necessary for mounting an element without increasing the parasitic capacitance. Further, in order to improve the receiving sensitivity, firstly, the light absorption layer may be thickened, but if it is thickened to a certain extent or more, the response speed is deteriorated due to the limitation of the transit time of the carrier, so it is not possible to make the thickness unlimited. Can not. Therefore, for example, in the case of a front-illuminated element, a reflective film is formed on the back surface of the element that is mirror-polished, and the back-reflected light is incident on the light absorption layer again to increase the effective absorption layer thickness, or A silicon nitride film is formed on the surface of the light receiving part, and its thickness is set to 1/4 of the wavelength in the film of incident light, so that surface reflection is suppressed to improve the receiving sensitivity. There is.

[0003]

P ⁺ − by selective diffusion
Consider an n-type planar InGaAs pin photodiode. In the case of an element having a structure in which a mesa region different from the light receiving portion is provided using a semi-insulating substrate, a p pad electrode is formed in this region, and this and the p ⁺ region are connected by step wiring,
Part of the step wiring passes over the n region via the passivation film. Parasitic capacitance is generated in this portion. In the element having such a structure, the same silicon nitride film is usually provided with two functions of a passivation film and an antireflection film. The wavelength of light normally used in optical communication is 1.3 μm to 1.
It is 55 μm, and the film thickness of this silicon nitride is usually 1/4 of the wavelength in the film of this light. Therefore, the thickness of this silicon nitride film is as thin as about 0.2 μm, and there is a problem that the above-mentioned parasitic capacitance becomes large. In order to prevent this increase in parasitic capacitance, for example, there is a method in which a sufficiently thick silicon nitride film is first formed and then only the film thickness of the light receiving portion is set to about 0.2 μm by selective etching. However, in order to form the light receiving portion by this method, there is a problem that the PR process and the selective etching process are additionally required. An object of the present invention is to provide a semiconductor light receiving element that solves such problems.

[0004]

In order to solve the above-mentioned problems, a semiconductor light receiving element provided by the present invention has a passivation film / antireflection film on the element surface, and the film thickness of the incident light is The wavelength is (2n + 1) / 4 times (n is a natural number) in the film.

[0005]

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

FIG. 1 is a schematic sectional view of a pin photodiode showing an embodiment of the present invention. The structure of this embodiment will be described together with its manufacturing process.

First, n ⁺ -InP2, n ^-- InGaAs3 are sequentially formed on the semi-insulating InP substrate 1 by vapor phase epitaxy.
The crystals of the n-InP layer 4 are stacked. After that, a pn junction having a diameter of 40 μm is formed by InGaAs3 by selective thermal diffusion of Zn.
Form inside. Next, the mesa 6 including the light receiving portion and the mesa 7 for the p-pad electrode are formed by selective etching. These mesas are electrically separated by performing the etching at this time until reaching the semi-insulating substrate 1. afterwards,
A silicon nitride film 8 is formed on the device surface by plasma CVD. The film thickness at this time was 3/4 times the wavelength of the incident light in the film. Finally, the p-side electrode 9 and the n-side electrode 10 are formed. The p-side electrode 9 has a structure in which the contact electrode portion on the p ⁺ region 5 and the pad electrode portion are connected by a step wiring.

Next, the silicon nitride film 8 will be described in detail. This film also serves as a passivation film and an antireflection film. Since the film has a function as an antireflection film and it is preferable that the film thickness be as thick as possible in order to reduce parasitic capacitance, the film thickness of this film is 3 times the wavelength of incident light in the film.
/ 4 times. By doing so, it is possible to omit the step of changing the film thickness on the light receiving portion and on the other portion.

In this example, the case where the film thickness of the silicon nitride film 8 is set to 3/4 times the wavelength of the incident light in the film is shown, but it is not limited to 3/4 times and (2n + 1) / 4 times. If (n is a natural number), the same effect can be obtained.

[0010]

As described above, according to the present invention, a semiconductor light receiving element having a small parasitic capacitance and an excellent high-speed response can be obtained in a small number of steps.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a pin photodiode showing an embodiment of the present invention.

[Explanation of symbols]

1 Semi-insulating InP substrate 2 n ⁺ -InP 3 n ^-- InGaAs 4 n -InP 5 p ⁺ region 6 Mesa including light receiving part 7 Mesa for p pad electrode 8 Silicon nitride film 9 p-side electrode 10 n-side electrode

Claims (1)

[Claims] 1. A device has a passivation film and an antireflection film on the surface thereof, and the film thickness is (2) the wavelength of the incident light in the film.
n + 1) / 4 times (n is a natural number).