JPS62219518A - Formation of electrode of compound semiconductor element - Google Patents

Abstract

PURPOSE:To form a compound semiconductor element having both excellent adhesive strength with a semiconductor and low contact resistance by a method wherein a Ti/Pt multilayer metal film is formed on the region where a compound semiconductor is selectively exposed using an insulating film, and a second multilayer metal film, consisting of a metal film containing at least one of Ti, Pt, Pd and W, and the Au film provided on the surface of said metal film, is formed by making ion beam mixing take place. CONSTITUTION:An insulating film 2 is formed on the surface of a compound semiconductor 1, a photoresist 3 is coated thereon, the insulating film 2 located on the specific region is removed, and a Ti/Pt 5 film is vapor-deposited. An ion-beam mixing is performed by implanting B<+> ions, the photoresist is exfoliated, the Ti 4/Pt 5 is selectively left, an alloy of an electrode metal and a semiconductor is formed by performing a heat treatment in the above-mentioned state, and an ohmic electrode is obtained. A photoresist 6 is coated, and the photoresist on the specific region is removed by performing exposing and developing treatments in such a manner that the surface of the insulating film 2 located on the Pt 5 surface and its circumference will be exposed. A Ti 7/Au 8 are vapor-deposited, and lastly, the photoresist is exfoliated, and the bonding pads Ti 7/Au 8 are selectively formed on the specific region using a lift-off technique.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for forming electrodes of compound semiconductor devices.

[Conventional technology]

Compound semiconductors have been widely used in optical communication devices, etc., but in some cases these devices can be used under harsh conditions.
It is also used in situations where maintenance is difficult. Therefore, these devices are required to have not only excellent characteristics but also high reliability depending on the environment in which they are used. One of the factors that most affects reliability is electrode deterioration that progresses due to the reaction between the electrode and the semiconductor. Conventionally, ohmic electrodes having a structure in which a metal containing a small amount of doping impurities (Zn, Ge, etc.) is brought into direct contact with a semiconductor have been widely used as electrodes of semiconductor devices. However, in this electrode structure, the expanded Au
Because it reacts with semiconductors at temperatures as low as 00°C, it has sometimes caused significant deterioration of the characteristics of electronic devices. To improve this, Ti
, Ti/Pt (
Also, electrodes with a 1d Pd , W ) /Au multilayer structure have attracted attention. The Ti/Pt/Au electrode is made of Ti4 as a contact layer on the surface of the compound semiconductor 10 as shown in FIG.
f: It has a three-layer structure in which Au8 is used as a bonding pad and Pt5, a high melting point metal, is sandwiched between the two layers as a barrier metal for the Au.It is a typical multilayer structure electrode. It is attracting strong interest. Note that 2 is an insulating film.

[Problem that the invention seeks to solve]

However, although Ti/Pt/Au-based electrodes provide thermally stable and highly reliable electrodes, they hardly form an alloy layer with the underlying semiconductor, and the electrodes tend to peel off easily and have low contact resistance. The problem was that it was expensive. Electrode peeling caused a significant drop in device yield. In addition, high contact resistance is not just a hindrance to high-speed operation, but also causes deterioration due to surges, and Ti
Solving these problems with /Pt/Au based electrodes has been a major challenge.

An object of the present invention is to provide a method for forming an electrode for a compound semiconductor device, which eliminates the above-mentioned conventional drawbacks, has high reliability, has excellent adhesion to a semiconductor, and has low contact resistance.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a method for forming an electrode of a compound semiconductor, in which a first multilayer metal film made of Ti/Pt is formed in a region where the compound semiconductor is selectively exposed by an insulating film. a step of ion-implanting doping atoms into the metal thin film to cause ion beam mixing between the metal film and the compound semiconductor surface layer, a heat treatment step, and the first multilayer metal film and its surroundings. forming a second multilayer metal film consisting of a metal film containing at least one of Ti, Pt, Pd, and W and an Au film provided on the surface of the metal film in the region including the insulating film of the second part; shall be.

[Effect]

The present invention solves the problems of the prior art with the above-described configuration. That is, when the first multilayer metal film is formed, doping atoms are ion-implanted, ion beam mixing is performed at the metal-semiconductor interface, and in conjunction with the subsequent heat treatment step, the metal-semiconductor alloy is isometrically formed. This makes it possible to promote the progress of chemical transformation. In addition, doping atoms ion-implanted near the semiconductor surface also enter, increasing the surface impurity concentration and making it possible to reduce multi-contact resistance. Also, the first
Since the multilayer metal MK does not contain Au, the Au does not react with the semiconductor during heat treatment (such as forming alloy spikes), thereby preventing deterioration of device characteristics. The second multilayer metal film, which serves as a bonding pad, is formed on the selectively exposed surface of the first multilayer metal film and the surface of the insulating film in the vicinity thereof, thereby ensuring close contact between the metal and the insulating film. Because of its high properties, it is possible to obtain a highly reliable electrode with excellent overall electrode adhesion strength and low contact resistance.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, an example of forming a P-side electrode of a ■-■ group compound semiconductor will be described. First, an insulating film 2 is formed on the surface of a compound semiconductor 1 as shown in FIG. (As shown in bJ, a specific region of the insulating film 2 is removed by etching to expose the surface of the compound semiconductor 1. After that, a Ti4/Pt5 film is deposited as shown in Fig. (C1). As shown in dl, Be, which is a P-type dopant, is ion-implanted and ion beam mixing is performed.Next, the photoresist 7 is peeled off, and Ti4/Pi5 is left selectively only in specific areas using a lift-off technique. In this state, heat treatment is performed to form an alloy of the electrode metal and the semiconductor to obtain an ohmic electrode (Fig. Then, remove the photoresist in a specific area so that the Pts surface and the surface of the insulating film 2 around it are exposed.Next, as shown in Figure (f), Ti7/Au8 is deposited, and finally, photoresist is removed. (Remove the resist and apply lift-off technology to bonding pad)
Ti7/Au8 is selectively formed in the constant region (Figure (h) =).

Next, the process shown in FIG. 4(d) will be explained in detail using FIG. 2. Ti/Pt deposited on a semiconductor has a steep interface as shown in Figure 2 (al).
/Pt-based electrodes do not form a #1 alloy layer with the underlying semiconductor layer even when subjected to heat treatment, and as a result, the electrodes tend to peel off easily and have high contact resistance. According to the present invention, as shown in FIG. 2(b), by ion-implanting Be, which is a P-type dopant, into the deposited Ti/P film and performing ion beam mixing, the interaction between sTs and the semiconductor is achieved. It is possible to disturb the steepness of the interface and mix Ti atoms into the semiconductor surface layer. Subsequently, heat treatment is performed to obtain the effect of promoting alloy progress equivalently.

Furthermore, it is known that a compound of Ti and Pt contributes to the stopper effect as a barrier metal for Au, and in this regard, according to the present invention, Ill i and P
Because the mixing of t makes it easier to form a silica compound,
The device also has excellent reliability under high temperatures. Also Ti/Pt'
The Be that has passed through i and reached the semiconductor surface layer increases the P-type impurity concentration in the semiconductor surface layer, contributing to a reduction in contact resistance. Here, a sufficient mixing effect can be obtained with Ti/Pt/semiconductor, and the acceleration voltage t" is 150 kV and the implantation amount is 1Xl0 cm so that the Be+ ions themselves reach the semiconductor surface layer.
, Ti and Pt layer thicknesses were set to 800A and 1200A, respectively.

Furthermore, according to the present invention, the first Ti/Pt metal film has A
Since it does not contain u, Au will not react with the semiconductor during heat treatment and will not cause alloy spikes or other deterioration in device characteristics.

In addition, the second Ti/Au metal film is the Ti/Au metal film of the first layer.
The electrode wire is formed so as to be bound to the surface of the Pt metal film and the surrounding insulating film, and the electrode wire does not come loose due to the high adhesion between the metal and the insulating film. Furthermore, since there is no part of the semiconductor surface exposed to the atmosphere in the finished structure, there is no concern about surface deterioration.

In addition, in the above example, T was used as the metal film immediately inside the Au.
Although the case is shown in which Ti is used, Pd, Pt,
Similar effects can be obtained with W and combinations thereof.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain an electrode for a compound semiconductor device that is highly reliable, has excellent adhesion, and has low contact resistance.

[Brief explanation of drawings]

Figures 1 (a) to (h) are schematic cross-sectional views showing the manufacturing process of an embodiment of the present invention, and Figures 2 (a) and (b) are Figure 1 (
A schematic diagram conceptually showing the state of the interface between a metal atom and a semiconductor to explain the step d).
FIG. 2 is a schematic cross-sectional view of a compound semiconductor device having an electrode with a /P t/Au three-layer structure.

Claims (1)

[Claims] A step of forming a first multilayer metal film made of a Ti/Pt film in a region where the compound semiconductor is selectively exposed by the insulating film, and ion-implanting doping atoms into the metal film to form a surface layer of the metal film and the compound semiconductor. a step of causing ion beam mixing between the
Ti, Ti,
A method for forming electrodes of a compound semiconductor device, comprising the step of forming a second multilayer metal film consisting of at least one metal film of Pt, Pd, and W and an Au film provided on the surface of the second multilayer metal film.