JPS604214A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a reversal direction leakage current of a Schottky junction by a method wherein Al is deposited on a main surface of a gallium arsenite wafer and, after a heat-treatment, the aluminium layer and a reactive product layer are removed by etching and then a junction electrode is formed. CONSTITUTION:A thin N type layer 5 is formed on the main surface of an N<+> GaAs substrate 4 by an epitaxial growth. An SiO2 film 2 is formed on the surface of the thin layer 5 and a part of the SiO2 film where a Schottky junction is to be formed is removed by etching and the N type layer is exposed. After an aluminium layer 6 is formed on the whole surface, a thin GaAlAs layer 7 is formed by a heat-treatment of the GaAs wafer. Because of a diffusion during the heat-treatment, impurities of the surface of the N type layer 5 and heavy metals are captured into the GaAlAs layer 7 and removed with the aluminium layer 6 and the GaAlAs layer 7 by a hydrochloric acid etching. The tantallum layer 8 is deposited and a metal layer 9 is deposited on the tantalum layer 8 and the metal layer 9 and the tantallum layer 8 other than the electrode part are removed by an etching. Then on the backside of the substrate 4, an ohmic electrode 10 made of a gold/germanium alloy is formed. With this constitution, a reversal direction leakage current of the Schottky junction can be reduced and a contact resistance between the electrode metal and the GaAs wafer can be made uniform with low resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor device in which a bonding electrode is formed on the main surface of a gallium arsenide (C, aAs) wafer.

[Technical Background of the Invention and Problems Therewith] Generally, semiconductor devices operate by transmitting and receiving electrical signals through electrodes, so the role of the electrodes is extremely important.

Conventionally, when forming electrodes on a GaAs wafer, first,
As shown in FIG. 1 (lL), the acid surface of the electrical substrate of the n + GaAs substrate I is treated by a chemical method, and a silicon dioxide film (SIO2 film) 2, which is an insulator, is deposited on the surface.
Furthermore, a window is opened in the S102 film 2 into a predetermined shape using photoetching (hereinafter referred to as PEP). Then the first
As shown in figure (b).

The surface of the GaAs substrate is etched, and a metal film is further deposited on the entire surface by vacuum evaporation to form an electrode metal 3.
Etch and remove unnecessary metal film using EP. Thereafter, a desired electrode is obtained by performing heat treatment or the like.

However, in electrodes manufactured by such a method, impurities and heavy metals generated by processes such as PEP and etching adhere to the interface between the GaAs substrate and the metal that forms the bond, especially when forming a Schottky junction. These impurities and heavy metals can act as a cause of increasing reverse leakage current in Schottky junctions, and even in the case of ohmic contacts, they can cause rectification in the voltage-current characteristics, making it difficult to obtain uniform and low contact resistance over the entire contact surface. Inconveniences may occur, such as not being able to do so. In order to suppress this phenomenon, the exposed joint surfaces are generally machined.

Deeply removed with chi/g, high resistivity (15MΩ or more)
In order to deal with the above-mentioned disadvantages, washing the electrode repeatedly with pure water, adding a small amount of kermanium to the electrode forming metal, and performing heat treatment to reduce the contact resistance of the ohmic contact, etc. It is known as a relatively effective method. However, with the above methods, it is difficult to obtain a sufficiently clean GaAs surface no matter how carefully the pure water cleaning is performed, and even with the latter method, it is difficult to obtain a sufficiently clean GaAs surface with low contact resistance. It is often technically difficult to obtain ζ.

[Purpose of the invention]

The present invention has been made in view of the above circumstances.
Clean G that reliably removes impurities and heavy metals adhering to the substrate surface without causing any damage to the GaAs substrate.
By obtaining an aAs substrate surface, the reverse leakage current of the Schottky junction can be reduced.

Another object of the present invention is to provide a method for manufacturing a semiconductor device that can uniformly form a low contact resistance between an electrode metal and a GaAs substrate over the entire contact surface.

[Summary of the invention]

In the present invention, when forming an electrode on the main surface of a GaAs wafer, aluminum is deposited on the main surface of the GaAs wafer in advance and heat treated, and then the deposited aluminum layer and the gallium arsenide formed by the heat treatment are deposited on the main surface of the GaAs wafer. This is a method of manufacturing a semiconductor device in which a reaction product layer of aluminum is removed by etching, and then a required metal is deposited on the main surface of a GaAg wafer to form a bonding electrode.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

That is, FIG. 2 shows an embodiment in which a tantalum (Ta)-n-type GaAs Schottky barrier diode is applied to the present invention according to its manufacturing process. Figure 2 (,)
is a thin n layer on the main surface of the n+GaAs substrate 4 with a thickness of about 15 to 2.0 μm and a carrier concentration of 2×10”cm−3.
It is shown that the mold layer 5 was formed by an epicyclic growth technique. Furthermore, FIG. 2(b) shows that S is on the surface of this n-type layer 50.
An insulating film such as the iO2 film 2 is formed by the CVD method, and the S on the n-type layer 5 in the portion that will become the Schottky junction is formed using PEP.
This shows that the iO2 film 2 is etched away and the n-type layer 5 is exposed. Next, FIG. 2(C) shows the exposed n
It shows that an aluminum layer 6 of 2000i to 3000J was deposited on the entire surface including the mold layer 5 using a vapor deposition method. At this time, heating the substrate (about 100° C.) is effective because gas adsorbed on the exposed surface of the n-type layer 5 can be removed, contributing to surface cleaning. Next, the GaAs wafer thus formed is placed in a furnace in a reducing atmosphere (hydrogen gas) and subjected to heat treatment at a temperature of about 200° C. for 10 minutes. Through this heat treatment, the aluminum layer 6 penetrates into the n-type layer 5 in two-way contact with solid phase diffusion, forming a very thin GaAtAs layer 7, as shown in FIG. 2(d). Due to diffusion during this heat treatment, impurities and heavy metals adhering to the surface of the n-type layer 5 in contact with the aluminum layer 6 are taken into the GaklAs layer 7 which is reacted and produced as the diffusion progresses. After Gi,
Aluminum layer 6 and GaA are removed by treatment with hydrochloric acid.
The tAs layer 7 is etched, and the impurities and heavy metals incorporated therein are also removed at the same time.

Since hydrochloric acid has the property of hardly etching GaAs, only the aluminum layer 6 and G-S layer 7 can be dissolved and removed, and the GaAs wafer is not affected at all. Also, during this hydrochloric acid treatment, the n-type layer 5 of the electrode-shaped sensing part
A thin GaAs oxide film is formed on the surface of the n-type layer 5 and acts as a stable surface protection film, so that the exposed surface of the n-type layer 5 is never contaminated again. Furthermore, this oxide film has a thickness of several 10
Because it is extremely thin, it does not affect subsequent processes.

FIG. 2(e) shows that in order to completely form a Schottky junction, a Kunkle layer 8 of a high melting point transition metal is deposited, and furthermore, an undying layer 8 is deposited.
It is shown that a gold layer 9 is successively deposited on the tantalum layer 8 for the purpose of coating. In FIG. 2(f), the gold layer 9 and tantalum layer 8 other than the electrode portions are removed by etching using the glazma etching technique, and then 2-nopping and polyzono-nobbing are performed on the back surface of the 1+GaAs substrate 4 to completely remove the entire wafer layer. 10
In order to form an ohmic electrode with a thickness of 0 to 120 μm, gold-darmanium alloy 10 is deposited on the entire polished surface, and then heat-treated in a 400°C furnace for 10 minutes to form an ohmic electrode. This shows the final shape of the ohmic electrode. Aluminum has a lower deep impurity level density in GaAs than other metals, and in this sense it acts as an inert metal with respect to GaAs, and is extremely effective in the present invention. The figure shows the experimental results of the voltage-current characteristics of a Ta--GaAs Schottky diode manufactured by the conventional method and a Ta--GaAs Schottky diode manufactured by surface cleaning with aluminum according to the present invention.

As is clear from FIG. 3, the present invention can reduce the reverse leakage current of the Schottky junction. Here, A indicates the method according to the present invention, and B indicates the method according to the conventional method.

〔Effect of the invention〕

As described above, according to the present invention, when forming an electrode on the main surface of a GaAs wafer, GaA
Aluminum is vapor-deposited and heat-treated on the main surface of the wafer,
Thereafter, the reaction product f of gallium arsenide and aluminum formed by the vapor-deposited aluminum layer and heat treatment
By removing the tl etching and then depositing the required metal on the main surface of the GaAs wafer to form a bonding electrode, impurities and heavy metals adhering to the surface of the GaAs wafer can be removed by causing capillary damage to the GaAs wafer. Since it can be removed reliably and a clean GaAs wafer surface can be obtained, the reverse leakage current of the Schottky junction is reduced and the contact resistance between the electrode metal and the GaAs wafer is made uniform over the entire contact surface.

Moreover, it can be formed with low resistance. Furthermore, since a clean GaAg wafer surface can be obtained simply by removing the thin GaAtAs layer, it is possible to provide an extremely effective means for forming electrodes of GaAs semiconductor devices having a thin active layer.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a manufacturing process in a conventional semiconductor device manufacturing method υ, FIG. 2 is a diagram showing a manufacturing process in an embodiment of the present invention, and FIG. 3 is a diagram showing a manufacturing process in an embodiment of the present invention. FIG. 2 is a characteristic diagram showing an example of the current characteristics of the 'Booh-current characteristic in comparison with the conventional one. I... n+GaAs substrate, 2... silicon dioxide film, 3... electrode metal, 5... engineered axial n-type layer,
6... Aluminum layer, 7... GaAtAs layer,
8... Taftal layer, 9... Gold layer. Applicant's representative Patent attorney Takeshi Suzue Rice production Figure 1 (a) (b)

Claims (1)

[Claims] Aluminum is vapor-deposited and heat-treated on the main surface of the gallium arsenide wafer in advance, and then the vapor-deposited aluminum layer and the reaction product layer of gallium arsenide and aluminum formed by the heat treatment are removed by etching. 1. A method of manufacturing a semiconductor device, comprising forming a bonding electrode by vapor-depositing a required metal thereon.