JPS613477A - Manufacture of semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain the APD of excellent characteristic by good guard ring effect by enabling a semiconductor layer in which the light receiving region is embedded to be epitaxially grown without defects by forming a mask out of Si nitride. CONSTITUTION:Semiconductor layers 2-4 are successively epitaxially grown on an N type InP substrate 1. An Si nitride film is formed on the InP layer 4, and a circuar mask 5 is formed by patterning this film. Next, this layer is formed into a mesa by removing the periphery of the light receiving region. Then, an N type InP layr 6 is epitaxially grown in liquid phase as the buried layer. An acceptor impurity is diffused by providing a mask 7 after removal of the mask 5. This diffusion enables a P type region to be formed over the InP layer 4 of the light receiving region and the InP layer 6 of the buried layer. Since the layer 6 has an n type impurity concentration of approx. 1X10<15>cm<-3>, even the region in the skirt of the impurity diffusion turns into a P type region 9, resulting in the construction of a guard ring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor light receiving device, and particularly to an improvement in a method for manufacturing an avalanche photodiode provided with a guard ring.

In optical communications and other systems that use light as a medium for information signals, a semiconductor photodetector that converts an optical signal into an electrical signal is one of the basic components.
An avalanche photodiode (hereinafter abbreviated as APD) whose photocurrent is multiplied by avalanche breakdown is highly effective in improving the signal-to-noise ratio of a photodetector. A guard ring is often provided for the purpose of stably generating this avalanche breakdown, but there is a demand for an improvement in the manufacturing method in order to improve the characteristics of the APD.

[Conventional technology]

For example, as a semiconductor light receiving device for optical communication, the wavelength is 1.3.
It is necessary to adapt to a band of about 1.65 μm.

FIG. 2(a) is a sectional view showing one conventional example of an APD suitable for this wavelength band.

In the figure, 21 is an n+WInP substrate, 22 is an n-type InP substrate, and 22 is an n-type InP substrate.
23 is a GaAs light absorption layer, 23 is an Il-type InP film, 24 is a p + type region 25 formed in n-type InP#, is a p-type guard ring region, 26 is an antireflection film, 27 is a protective insulating film, 28
indicates p@J electrode, and 29 indicates nglQ electrode.

A high reverse bias voltage is applied to make the APDK n-side electrode 29 positive and the p-side electrode 28 negative.
Avalanche breakdown occurs in the vicinity of the pn junction of the n-type InP layer 23 using holes excited by the input signal light as primary carriers.

The guard ring region 25 is formed deeper than this around the normally circular p+ type region 24, and prevents breakdown around the p+ type region 24, which is likely to occur at a voltage lower than the avalanche breakdown. The purpose is to

As a manufacturing method of an APD equipped with a guard ring as in this conventional example, a mask for selecting either one of the p+ type region 4 and the p type guard ring region 25 is conventionally used.
``Many methods are used in which impurities are provided on conductor #23 and impurities are introduced separately by diffusion or ion implantation.

This manufacturing method requires impurity introduction treatment twice, and it is necessary to strictly control the impurity concentration, diffusion depth, lateral spread of diffusion, etc. in each case.

In order to deal with this problem, a manufacturing method in which the guard ring is formed by a buried growth layer has been developed, for example, in Japanese Patent Laid-Open No. 55
-99782.

According to this manufacturing method, as shown in the cross-sectional view of FIG. 2(b), a double layer 32 and an n-layer 33 are formed on the semiconductor to form a junction, and then, for example, Sin is coated on the surface of the semiconductor. This is then selectively etched using an appropriate method to leave a desired size as a mask 36. This mask 3
6, as shown in the figure, the portion of the semiconductor layer not covered by the mask 36 is etched to a depth deeper than the pn junction surface 34 is exposed.

Next, epitaxial growth is selectively performed on this semiconductor layer. Through this epitaxial growth, a new semiconductor layer 35 is grown only on the exposed semiconductor part excluding the mask. layer 3
5 is operated as a guard ring.

However, the guard ring formed by the liquid phase epitaxial growth method according to this manufacturing method has the following problems.

First, near the 5in2 mask 36 of the buried growth layer, ripple-like undulations 37 appear as schematically illustrated in FIG. 2(c), and the morphology of the surface of the growth layer is excellent.

This is a sign that the epitaxially grown layer is strained and non-uniform, especially near the important growth interface.

The light-receiving region of a semiconductor light-receiving device is usually circular, and the crystal direction of the interface of the buried growth layer changes periodically. Although this is significantly different from epitaxial growth for filling the striped region of a semiconductor laser, there are still many problems in epitaxial growth on a surface where the crystal direction changes in this way.

Furthermore, using the entire buried growth layer as a guard ring as in the invention results in an extremely large junction capacitance.

[Problem that the invention seeks to solve]

As mentioned above, selective epitaxial growth for burying the light-receiving region of a semiconductor light-receiving device is epitaxial growth on a surface where the crystal direction changes. It is necessary to improve the crystallinity in the vicinity.

[Means for solving problems]

The problem is that when a mask is provided to cover the upper light-receiving region of the semiconductor substrate, the periphery of the region of the semiconductor substrate is selectively removed, and then a semiconductor layer to fill the region is grown by liquid phase epitaxial growth, the mask is removed. This problem is solved by a method of manufacturing a semiconductor light receiving device according to the present invention, which is formed using silicon nitride.

[Effect]

In the present invention, selective etching and liquid phase epitaxial growth are performed using a mask made of silicon nitride that covers the light-receiving region.

Silicon nitride films, SiO□ films, etc. are flexible, and the stress exerted on the epitaxial growth layer is alleviated.

Note that the silicon nitride film is preferably formed by a plasma chemical vapor deposition method, and its thickness is preferably 60 nm or more and 200 nm or less.

〔Example〕

The present invention will be specifically explained below with reference to embodiments shown in step-by-step cross-sectional views in FIG.

Referring to FIG. 1(a), the following semiconductor layers 2 to 4 are successively epitaxially grown on an n-type InP substrate 1. 2 is the impurity concentration I x 10
"cm-3 + n-type InGaAs layer with a thickness of about 2 μm, 3
is an n-type I with an impurity concentration equivalent to this and a thickness of about 05 μm.
The nGaAsP layer 4 is also an n-type InP layer with the same impurity concentration and a thickness of about 3 μm.

Note that InGaAsPnGaAs layer 2As layer 2 to InP
A mask 5 covering the light-receiving region is provided on the InP layer 4 provided to facilitate the injection of holes into the n-type layer (see FIG. 1(b)).

In this example, a silicon nitride film with a thickness of about 1100 nm was formed by plasma chemical vapor deposition, and this was patterned by phosphorography to have a diameter of about 10 nm.
A circular mask 5 of 0 μm is formed.

Then, by melt-back or chemical etching method, etc.
As shown in the figure, the periphery of the light receiving area is removed to form a mesa shape.

At this time, for example, about 0.5 μm of n-type InPMf4 is left.

As the reference buried layer in FIG. 1(c), for example, the impurity concentration lXl01! ″(
An n-type InP layer 6 having a thickness of approximately m −' is grown by liquid phase epitaxial growth. In order to avoid deteriorating the surface of the InPn seed layer on which this InP layer 6 is grown, it is desirable to perform the previous mesa formation by meltback and then grow the InP layer 6 immediately. 65
The growth of the InP layer 6 is carried out using a solution of InP in an In solvent at an unsaturated level of 2°C at 0°C, and the InP layer 6 is continuously grown using an In solution of InP at a supercooling level of 5°C.

FIG. 1(d) The reference mask 5 is removed and a mask 7 is provided to diffuse acceptor impurities. As the acceptor impurity, for example, cadmium (Cd), zinc (Z'n), etc. are used.

Due to this diffusion, a p-type head region is formed across InPJM6, which is the InPn seed layer buried layer in the light-receiving region, but the n-type impurity concentration of InP#6 is I x 10.
Since it is about l5cWL-', the area up to the bottom region of the impurity diffusion becomes the p-type region 9, forming a guard ring.

On the other hand, since the InP layer 4 has a higher impurity concentration than this, the p-group region 8 of the light receiving region is shallower than the region 9.

In this embodiment, the high density area where a fairly uniform density can be obtained is larger than 10'7", and the area 8 is about 1.
5 μm, and region 9 is approximately 2 μm deep.

Refer to FIG. 1 (Corporation) Anti-reflection coating 10 according to the prior art. Protective insulating film 11, p
A side electrode 12 and an n-side electrode 13 are provided.

In the embodiments described above, the silicon nitride film serving as the mask 5 is formed by plasma chemical vapor deposition.
According to this manufacturing method, as has been often reported, elements other than silicon and nitrogen are included in the film, increasing its flexibility.

Furthermore, if the thickness of the silicon nitride film is less than 60 nm, there is a high possibility that pinholes will occur in it;
If the mask exceeds 100%, the rigidity becomes large and problems such as cracking of the mask due to thermal strain during growth are likely to occur.

By using a silicon nitride mask with such consideration, epitaxial growth can be achieved without unevenness of the buried layer, distortion of the crystal, deformation of the pattern, etc.

〔Effect of the invention〕

As described above, the manufacturing method of the present invention makes it possible to epitaxially grow the semiconductor layer burying the light-receiving region without defects, and provides an APD with excellent characteristics due to the good guard ring effect.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an embodiment of the present invention in the order of steps, and Fig. 2 (
Figures a) and (b) are cross-sectional views of the conventional example, and figure (c) is a plan view of the main parts thereof. In the figure, ■ is an n-type InP substrate, 2 is an n-type InGaAa layer, and 3 is an n-type InP substrate.
is an n-type InGaAsP layer, 4 is an n-type InP layer, 5 is -r
6 is n-type InP layer, 8 is p-type head area
9 is a p-type guard ring region, 10 is an antireflection film,
11 is a protective insulating film, 12 is a pflll electrode
13 indicates an n-side electrode. - Part 1 ■ Fig. 1 Fig. 2

Claims (3)

[Claims] (1) A mask covering a light-receiving region is provided on a semiconductor substrate, the area around the region of the semiconductor substrate is selectively removed, and then the mask is nitrided when a semiconductor layer to fill the region is grown by liquid phase epitaxial growth. A method for manufacturing a semiconductor light receiving device, characterized in that it is formed using silicon. (2) The method of manufacturing a semiconductor light receiving device according to claim 1, wherein the silicon nitride used for the mask is deposited by a plasma chemical vapor deposition method. (3) The thickness of the mask is 60 nm or more and 200 nm
3. The method of manufacturing a semiconductor light-receiving device according to claim 2, wherein the distance is less than or equal to m.