JP3123217B2 - Method of forming ohmic electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an ohmic electrode, and more particularly to a method for forming an ohmic electrode in a compound semiconductor layer containing Ga as a constituent.

[0002]

2. Description of the Related Art Conventionally, AuGe or N is formed on a GaAs semiconductor layer formed in a GaAs compound semiconductor device.
An ohmic electrode is formed by alloying a metal layer made of i-AuGe. Ohmic electrodes are
For example, Au-Ge is formed on the n-type GaAs compound semiconductor layer.
(12% by weight) layer and a Ni layer are formed in this order by a vacuum deposition method, and then alloyed at 400 to 450 ° C. By this alloying treatment, Au-G
Dissolution of e occurs and a liquid phase is formed. At this time, n-type G
Since the surface of the aAs compound semiconductor layer is in an unsaturated state, A
Au-Ga dissolved in u-Ge solution and excess As
And an alloy layer composed of Ni-As-Ge composed of Ni and Ge. Next, an electrode material layer is deposited on the alloy layer, and the electrode material layer is further etched into a desired shape to complete an ohmic electrode.

[0003]

The alloy layer contains β-
It is known that AuGa is generated. β-AuGa
As a result, the alloy layer becomes thermally unstable. That is, β
The melting point of AuGa is about 360 ° C., which is about the same as the processing temperature of various steps that must be performed after the formation of the alloy layer, for example, the formation of the SiN layer by the CVD method at about 350 ° C. Therefore, when the ohmic electrode is exposed to the processing temperature in such a post-process, there is a problem that the contact resistance of the electrode is increased (for example, the literature "De"
velopmentof Ohmic contact materials for GaAs integ
rated circuit ", M. Murakami, Material Science Repo
rts 5 (1990), pp273-317). Furthermore, even at room temperature, the contact resistance of the electrode increases, albeit at a low speed. Such a phenomenon also occurs in an ohmic electrode formed by alloying a metal layer made of AuGe.

Due to such a phenomenon, AuGe or N
An ohmic electrode made of an alloy layer formed by alloying a metal layer made of i-AuGe has a problem of poor reliability.

Accordingly, it is an object of the present invention to provide a method for forming a thermally stable, highly reliable ohmic electrode on a compound semiconductor layer containing Ga as a constituent.

[0006]

Means for Solving the Problems The present inventor has proposed a Ni—Au
When the composition in the thickness direction of the alloy layer formed by alloying the metal layer made of Ge was analyzed, the surface layer of the alloy layer mainly contained Au and Ga, and the alloy layers other than the surface layer mainly contained Au and Ga. Contained Ni-As-Ge in the present invention, and completed the present invention. That is, the method for forming an ohmic electrode according to the present invention includes the following steps: (a) forming a compound semiconductor layer containing Ga
A step of forming a metal layer containing Au; (b) a step of subjecting the metal layer to alloying to form an alloy layer; and (c) a step of removing a surface layer mainly containing Au—Ga in the alloy layer . (D) depositing an electrode material layer on the alloy layer from which the surface layer has been removed.

In one aspect of the method for forming an ohmic electrode of the present invention, the metal layer is preferably composed of two layers, an AuGe layer and a Ni layer.

[0008]

In the process of forming an alloy layer by subjecting a metal layer formed on a compound semiconductor layer containing Ga as a component to an alloy layer, Au moves to the surface of the alloy layer, and the surface of the alloy layer is mainly Au. And a layer containing Ga. In the method of the present invention, since the surface layer is removed by etching or the like, the above-mentioned thermally unstable β-AuGa hardly exists in the ohmic electrode, and as a result, a thermally stable ohmic electrode is obtained. be able to.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for forming an ohmic electrode according to the present invention will be described with reference to the drawings based on embodiments. First, a GaAs-based compound semiconductor is manufactured by a conventional method. As shown in a schematic partial cross-sectional view of FIG. 1A, the compound semiconductor layer 10 containing Ga as a component of the uppermost layer is an n-type G
It consists of an aAs compound semiconductor layer. In regions other than the regions where the ohmic electrodes of the compound semiconductor layer 10 are formed, for example, S
An insulating layer 12 made of iN is formed by a normal CVD method or the like. Note that the insulating layer 12 can be omitted in some cases.

Next, a metal layer containing Au is formed on the compound semiconductor layer 10. The patterning of the metal layer can be performed by a lift-off method. This metal layer 14 containing Au
Is a 200 nm thick Au from the compound semiconductor layer 10 side.
A Ge (12% by weight) layer 16 and a 50 nm-thick Ni layer 18 formed thereon (see FIG. 1A). These layers can be formed by, for example, a vacuum evaporation method or other various film formation methods. In this state, the metal layer 14 has a Schottky junction with the underlying compound semiconductor layer 10, and the current-voltage characteristics are not ohmic but show rectification.

Thereafter, an alloying process is performed on the metal layer 14 to form an alloy layer 20. The alloying process is performed, for example, at 450 ° C.
This is a heat treatment for one minute. Note that the temperature and time in the heat treatment can be appropriately changed. Thereby, GaAs in the compound semiconductor layer 10 and Ni-AuG in the metal layer 14 are formed.
reacts with e to form an alloy. FIG. 2 shows the result of Auger analysis of the composition in the thickness direction of the alloy layer 20 and the compound semiconductor layer 10 containing Ga as a constituent. The surface layer of the alloy layer 20 contains much Au. That is, G
A layer 22 mainly composed of Ni-As-Ge is formed on the aAs semiconductor layer 10, and Au has moved to the surface of the alloy layer. FIG. 1B schematically shows this state, and the alloy layer 20 is mainly composed of Ni—As— from the GaAs semiconductor layer 10 side.
It has a two-layer structure of a layer 22 containing Ge and a surface layer 24 mainly containing Au-Ga.

Next, the surface layer 24 of the alloy layer 20 is removed by an etching method. The thickness of the surface layer to be removed is about 20 to 80% of the total thickness of the alloy layer. As an etching method, for example, an ion milling method or I ₂ : NH ₄ I: H ₂
A wet etching method using an etchant composed of O: C ₂ H ₅ OH can be used. The alloy layer 20 remaining after the surface layer 24 mainly containing Au and Ga is removed by etching is a layer mainly containing Ni-As-Ge. The contact between the alloy layer 20 and the compound semiconductor layer is basically the same as the alloy layer made of Ni—As—Ge formed by the conventional method, and the ohmic electrode formed by the method of the present invention is: The contact resistance is about the same as that of an ohmic electrode formed by a conventional method. However, the surface layer 24 mainly containing β-AuGa which is thermally unstable is removed. Therefore, the ohmic electrode becomes thermally stable.

Next, as shown in FIG. 1C, the alloy layer 20 from which the surface layer 24 mainly containing Au and Ga has been removed,
That is, the electrode material layer 26 is formed on the layer mainly containing Ni-As-Ge.
Is deposited in a conventional manner. The electrode material layer 26 is, for example, a 50 nm thick Ti layer, 50 n
A W layer having a thickness of m, a Ti layer having a thickness of 50 nm, a Pt layer having a thickness of 50 nm, and an Au layer having a thickness of 500 nm can be used. These electrode materials can be deposited by, for example, a vacuum evaporation method. Thereafter, the electrode material layer 26 is patterned by an ion milling method or the like to obtain a desired electrode shape. In the electrode material layer, the lowermost Ti layer is used for improving the adhesion to the alloy layer 20, and the W layer is used for the electrode material layer (Ti-Pt in this embodiment) formed thereon. —Au layer) to suppress an intermetallic reaction.

Although the present invention has been described based on the preferred embodiment, the present invention is not limited to this embodiment. With the method of the present invention, an ohmic electrode can be formed on an n-type GaAs substrate. AuGe can be used as the metal layer containing Au. As the compound semiconductor layer, other than GaAs, AlGaAs, InG,
Compound semiconductors containing Ga as a constituent such as aAs can be given.

[0015] The method of the present invention comprises a MESFET, a JFE
The present invention can be applied to the manufacture of various devices requiring ohmic contact, such as various compound semiconductor devices such as T, HEMT, and HET, semiconductor lasers, light receiving elements, and the like.

[0016]

According to the method of the present invention, β-AuGa which causes thermal instability of the ohmic electrode is removed from the alloy layer. Therefore, various processes performed after the formation of the alloy layer, for example, the CV of the SiN layer as the interlayer insulating layer
Even if the ohmic electrode is exposed to a high temperature in the formation process by the method D, the contact resistance of the electrode does not increase. In addition, AuGe or Ni-type is formed on a compound semiconductor layer containing Ga as a component such as MESFET or JFET.
The reliability of a compound semiconductor device, a semiconductor laser, and a light receiving element having an alloy layer formed of AuGe can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view of a compound semiconductor device for explaining a method of forming an ohmic electrode according to the present invention.

FIG. 2 is a diagram showing Auger analysis results in the thickness direction of an alloy layer and a compound semiconductor layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Compound semiconductor layer containing Ga as a constituent 12 Insulating layer 14 Metal layer 16 AuGe layer 18 Ni layer 20 Alloy layer 22 Layer mainly containing Ni-As-Ge 24 Layer mainly containing Au and Ga 26 Electrode material layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/28 H01L 29/80 H01L 31/02 H01L 33/00 H01S 5/042 H01S 5/323

Claims (3)

(57) [Claims] 1. A method for forming an ohmic electrode on a compound semiconductor layer containing Ga as a constituent component, comprising: (a) forming a metal layer containing Au on the compound semiconductor layer; (C) removing a surface layer mainly containing Au—Ga in the alloy layer ; and (d) forming an electrode material layer on the alloy layer from which the surface layer has been removed. Depositing an ohmic electrode. 2. The metal layer includes an AuGe layer and a Ni layer.
The method for forming an ohmic electrode according to claim 1, comprising a layer. 3. Primarily Ni before Symbol alloy layer surface is removed
-As-Ge is contained.
Or the method of forming an ohmic electrode according to claim 2.