JPS61156786A - Manufacture of semiconductor luminescent device - Google Patents

Abstract

PURPOSE:To prevent the Au film from penetrating the semiconductor layer and to prevent the bad effect of the Au film by a method wherein a Ti film and a Pt film are adhered on the upper surface of the semiconductor substrate in such a way that at least one side of the Ti film and the Pt film is brought into an amorphous state. CONSTITUTION:The semiconductor substrate formed with a P-type InGaAsP contact layer 5 on its uppermost surface is placed in the chamber of the electron beam evaporating device and the substrate is cooled by liquid nitrogen and is made to drop to an absolute temperature of 77 deg.K. The interior of the evaporating chamber is made vacuous, and a Ti film 11 and a Pt film 12 are continuously evaporated on the upper surface of the semiconductor substrate by an electron beam evaporation method. So that the films 11 and 12 in an amorphous state are formed. Then, an Au film 13 is evaporated thereon. According to such a forming method, the film 11 and the film 12, which are adhered in an amorphous state, are hard to crystallize, and even though the films 11 and 12 are crystallized, pinholes are hard to generate. Accordingly, the Au film is prevented from penetrating the semiconductor layer and is prevented from being diffused in the semiconductor layer. As a result, the characteristics of the semiconductor laser can be made to improve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a semiconductor light emitting device, and particularly to a method of forming electrodes of a semiconductor laser or a light emitting diode.

Recently, optical transmission has been in the spotlight, and light-emitting diodes and semiconductor lasers are used as light sources.These light sources are made of a heterojunction structure of m-v compound semiconductors, and are particularly difficult to transmit coherent light. Semiconductor lasers that emit light are considered to be the most promising light sources for optical transmission. For example, ^lGaAs/GaAs in the wavelength band of 0.7 to 0.9 μm
(active M/substrate) and InGaA in the wavelength band of 1 to 1.5 μm
sP/InP is a well-known luminescent light source.

In such semiconductor lasers or light emitting diodes, it is desired to increase the luminous efficiency and extend the life span as much as possible, in other words, to improve the performance and reliability.

[Prior Art] The figure shows an example of such a light-emitting device.
This figure shows a schematic cross-sectional view of one type of GaAs P/In P semiconductor laser.
te Buri-ed tleterostruct
(ure type) embedded type laser.

In the figure, 1 is an n-InP substrate, 2 is an n-InPn flange 1 hood layer. 5 is a p-111GaAs P contact layer, 6 is a p-InP layer (current blocking layer), and an n electrode (+ electrode) 10 is provided on the upper surface of the contact layer 5, which is a titanium (Ti) film (film thickness 1000 mm). Fixed number of people 1, platinum (
Pt film (film thickness: approximately 1000) 2, gold (Au) film 1
It has a structure in which three layers (thickness: 3 μm) are laminated.

Further, an n-electrode (-electrode) 20 is formed on the back surface of the InP substrate 1, and is an electrode made of gold-germanium nitride.

In such a buried laser, the laser emission is confined by the current blocking layers on both sides, and the n-1nGaA
This is carried out in the sP active layer 3, and has the characteristic that a particularly low threshold current can be obtained.

[Problems to be Solved by the Invention] Incidentally, in the semiconductor laser or other light emitting device exemplified above, there is no problem since the n-electrode 20 is formed on the back surface of the thick substrate, but the p-electrode lO Since the layer is formed on a thin layer (layer close to the active layer) of the epidermis, it has a big impact on reliability.

That is, the Ti sieve film 1 and the Pt film 12 are successively formed by electron beam evaporation, and then the Au film is formed by electroplating. It has been found that the Au film diffuses through these films, reacts with the semiconductor layer, and deteriorates device characteristics. Furthermore, Au may penetrate during operation and deteriorate the light emitting characteristics.

These problems were detected by Auger electron spectroscopy analysis and
It has become clear.

The reason for this is that the Ti film and Pt film are very thin, and the deposited Ti film and Pt film are in a mixed state of amorphous and polycrystalline, and the ^U penetrates through the gaps unique to the crystal structure. Seem.

Furthermore, when observing the pinholes after these Ti films and Pt films were deposited, the pinhole density was 10'F/cni or more, which is also considered to be the cause of Au permeation.

On the other hand, the reason why the p-electrode IO has a Ti-Pt-Au three-layer structure is because Pt and the sieve easily react with the semiconductor layer, so Ti is interposed between the semiconductor layer and the sieve. , and because it easily reacts with Ti and Au, P
t is interposed therebetween.

Furthermore, the reason why the Ti film and Pt film are formed at a constant thickness of about 1000 is that if they are deposited too thickly, their thermal expansion will be significantly different from that of the semiconductor layer, which will cause stress to occur in the semiconductor layer. This is because there is a problem in that it causes distortion and affects the light emission characteristics.

The present invention eliminates these problems and improves performance.
This paper proposes a method for forming highly reliable electrodes.

[Means for solving the problem] The problem is to form a Ti film and a Pt film in succession on the upper surface of a semiconductor substrate so that at least one of them is in an amorphous state, and then to form an Au film on the Pt film. The problem is solved by a method of manufacturing a semiconductor light emitting device, which includes a step of forming an electrode with a three-layer stacked structure.

For example, this semiconductor substrate is cooled to a temperature of 100°K or less, and a Ti film and a Pt film are successively formed on the upper surface of the semiconductor substrate. Moreover, such a three-layer electrode is made of p-InGaA
Connect to the contact layer made of sP.

[Function] - That is, in the present invention, the semiconductor substrate is heated to a temperature of 100" or less,
That is, the Ti is cooled to about liquid nitrogen temperature (77°K).
At least one of the film and the Pt film is deposited in an amorphous state. Of course, it is preferable that both films be deposited in an amorphous state.

As a result, the film becomes dense and does not crystallize even after heat treatment, thus preventing the film from penetrating.
Its negative effects are prevented.

[Example] Hereinafter, the formation process will be explained in detail using examples.

p-In Ga AsP (0<x<1.0<y<1
) is placed in a chamber of an electron beam evaporator and cooled to 77°K with liquid nitrogen. Then, the degree of vacuum in the evaporation chamber was set to 1O-6 Torr or less, and a Ti film 11 with a thickness of 1000 nm was deposited on the top surface using the electron beam evaporation method.
．． Pt1l odor 12 with a film thickness of 1000 was applied continuously. In this way, a film in an amorphous state (non-crystalline state) is formed.

Next, this is heat-treated at 430° C. for 30 minutes in a hydrogen atmosphere. This is a process to ensure sufficient ohmic contact with the contact layer. Next, a U film having a thickness of 3 μm is deposited thereon by a normal electrolytic plating method.

Next, an n-electrode 20 with a thickness of 2000 was deposited, and further,
Heat treatment is performed at 380° C. for 1 minute, and finally, the semiconductor laser is finished by folding.

According to such a formation method, the Ti film and Pt film deposited in an amorphous state are difficult to crystallize, and even if crystallized, pinholes are not formed (the density of the pinholes is 1).
It has been confirmed that it is less than 0.03 /clIl. Moreover, according to this formation method, the Au concentration of the contact layer was below the detection limit of Auger electron spectroscopy. Analysis using the Rutherfort backward lt&random method was also outside the detection limit.

Although the above embodiment is a VSB type buried semiconductor laser, it goes without saying that it can also be applied to other BH type or PBH type semiconductor lasers or light emitting diodes.

[Effects of the Invention] As is clear from the above description, according to the present invention, transmission and diffusion of Au into the semiconductor layer is eliminated, and a great effect is obtained in improving the characteristics and reliability of the semiconductor laser.

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view of a semiconductor laser according to an embodiment of the present invention. In the figure, 1 is an n-1nP substrate, 2 is an n-1nP buffer layer, 3 is an n-1nGaAs P active layer, 4 is a p-1nP cladding layer, 5 is a p-1nGaAs P contact layer, and 6 is a p-1nP layer.
1nP current blocking layer, 20 is one electrode, 10 is ten electrodes, 11 is Ti film, 12 is Pt
Membrane 13 indicates the ^U membrane.

Claims (3)

[Claims] (1) Step of forming an electrode with a three-layer stacked structure in which a Ti film and a Pt film are successively formed on the upper surface of a semiconductor substrate so that at least one of them is in an amorphous state, and then an Au film is formed on the Pt film. 1. A method of manufacturing a semiconductor light emitting device, comprising: (2) Cooling the semiconductor substrate at a temperature of 100°K or less,
Continuously forming a Ti film and a Pt film on the upper surface of the semiconductor substrate,
2. The method of manufacturing a semiconductor light emitting device according to claim 1, further comprising the step of forming an electrode having a three-layer laminated structure of forming an Au film on the Pt film. (3) The upper surface of the semiconductor substrate to which the above electrode is connected is p-
2. The method of manufacturing a semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is made of an InGaAsP (0<x<1, 0<y<1) layer.