JPH05291299A - Formation of metallic electrode - Google Patents

Abstract

PURPOSE:To provide a technique to form fine metallic films with good controllability on a compound semiconductor layer such as GaAs or the like. CONSTITUTION:After a protection film 102 of single atom layer level mainly consisting of S is formed on a GaAs layer 101, a part of the protection film 102 is selectively removed by irradiation of a focused energy beam, for example, an ion beam 103 to leave the protection film 102 only in the desired fine region. Next, a W film 104 is deposited only on the protection film 102 of the fine region by application of selective CVD technique of a metal, for example, W. Thereby, controllability within a fine region such as a line width of an energy beam, for example, ion beam 103 focused on the GaAs layer 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal electrode in a compound semiconductor device, and more particularly to a method for forming a fine metal electrode on the surface of a compound semiconductor.

[0002]

2. Description of the Related Art Compound semiconductors mainly composed of GaAs are Si
Electron mobility is higher than that of, and its application to ultra-high speed devices is being investigated. Among GaAs high-speed devices, for example, in order to achieve high speed and high performance of a field effect transistor (MESFET), it is effective to reduce parasitic components by miniaturizing the elements as in the Si device. In particular, by shortening the gate length to around 0.1 μm, there is a possibility of ballistic conduction of electrons, so that the device can be significantly improved in performance. In most cases, W or WSi metal having excellent heat resistance is used for the gate electrode of GaAs MESFET. For fine processing of W or WSi metal, for example, Dry Process Symposium (1984), II-2, p.
as described in p25-30, CF ₄ ,
Dry etching using a gas such as SF ₆ or NF ₃ is being studied.

[0003]

[SUMMARY OF THE INVENTION] CF ₄ described above, S
With a dry etching technique using a gas such as F ₆ or NF ₃ , it is difficult to control the processed cross-sectional shape and the gate length because a sufficient selection ratio cannot be obtained with the resist. Is impossible. Also,
Since the resist mask is patterned by the usual photolithography technique, it is difficult to perform fine processing of 0.3 μm or less.

[0004]

The oxide film on the surface of a compound semiconductor layer forming a gate electrode is removed, and then an ultrathin protective film containing S, Se and the like is formed on the compound semiconductor surface. Next, the ultrathin layer protective film containing S, Se and the like is removed except for the fine region where the gate electrode is formed by irradiation with energy rays. Then, a metal is selectively deposited on the compound semiconductor layer in the gate electrode formation region having the ultrathin layer protective film containing S, Se or the like.

[0005]

[Function] An ultrathin layer of S and Se formed on the surface of the compound semiconductor
By removing the desired area of the protective film including the like by irradiation with focused energy rays, a protective film in a fine area of the beam diameter of the converged energy ray (several nm or less in the case of electron beam) is formed on the compound surface. You can leave. On the surface of the compound semiconductor having a protective film containing S, Se, etc., Fermi level pinning is released, charge transfer occurs with adsorbed molecules, and metal deposition by CVD is possible.

[0006]

【Example】

<Embodiment 1> An embodiment of the present invention will be described with reference to the process chart shown in FIG. N-type Ga formed on the semi-insulating substrate 100
After the As layer 101 is immersed in a supersaturated ammonium sulfide solution, heat treatment (250 to 500 ° C.) is performed in a reduced pressure atmosphere to form a monatomic layer-level protective film 102 mainly containing S on the surface of the n-type GaAs layer 101. (Fig. 1 (a)). Next, a desired region of the sample was scanned with a focused ion beam 103 (Si ions, accelerating voltage of 50 kV) to selectively remove the protective film 102 (FIG. 1B). Then, the selective W-CVD technique is applied to the sample to apply the n-type GaAs layer 1
The W film 104 was selectively deposited on the protective film 102 patterned on 01 (FIG. 1C). The selective W-CVD conditions at this time are as follows: gas flow rate WF ₆ : 2 sccm, SiH
₄ : 1 sccm, total gas pressure 0.12 torr, substrate temperature 320 ° C.

Through the above steps, the W film 104 can be formed in a fine region on the GaAs layer 101. Here, although the W film 104 is deposited on the n-type GaAs layer 101 in this embodiment, other II such as InAs is used.
It is also applicable to the IV compound semiconductor layer.

<Embodiment 2> An embodiment of the present invention will be described with reference to the process chart shown in FIG. The active layer 201 made of n-type GaAs formed on the semi-insulating substrate 200 is immersed in a supersaturated ammonium sulfide solution, and then heat-treated (250 to 500 ° C.) in a reduced pressure atmosphere to form an active layer 201 made of an n-type GaAs layer. A monoatomic layer-level protective film 202 mainly containing S was formed on the surface of the (FIG. 2A). Next, electron beam 20
By the irradiation of No. 3, the protective film 202 other than the fine gate electrode formation region was removed (FIG. 2B). The acceleration voltage of the electron beam 203 is 50 kV and the beam diameter is about 20 nm. In addition, the protective film 202 was easily removed by heating the sample during electron beam irradiation.

Next, the selective W-CVD technique is applied to the sample to pattern the protective film 20 on the active layer 201.
Then, W was selectively deposited on the layer 2 to form the gate electrode 204 (FIG. 2C). The selective W-CVD conditions at this time are
The gas flow rate is WF ₆ : 2 sccm, SiH ₄ : 1 sccm, the total gas pressure is 0.12 torr, and the substrate temperature is 320 ° C. Next is AuGe /
The source / drain electrodes 205 made of Ni / Au were formed by an ordinary lift-off method to complete the MESFET (FIG. 2 (d)).

According to this embodiment, the gate electrode 204 can be formed in a fine region below the resolution limit of the ordinary photolithography technique without using dry etching. As described in the prior art, the MESFET can achieve significantly high speed and high performance by shortening the gate electrode 204.

[0011]

EFFECT OF THE INVENTION G of the same width as the focused energy ray width
The metal film can be formed in a fine region on the aAs layer with good controllability.

[Brief description of drawings]

FIG. 1 is a process diagram of a first embodiment of the present invention.

FIG. 2 is a process diagram of a second embodiment of the present invention.

[Explanation of symbols]

100 ... Semi-insulating substrate, 101 ... N-type GaAs layer, 10
2 ... Protective film, 103 ... Ion beam, 104 ... W film.

Claims (3)

[Claims] 1. A step of forming an ultrathin layer protective film on the surface of the compound semiconductor after removing the oxide film on the surface of the compound semiconductor layer, and irradiation of energy rays, whereby the ultrathin layer protective film in a desired region is formed. And removing the ultra-thin layer protective film on the compound semiconductor layer by a metal selective CVD technique without forming a metal on the surface of the compound semiconductor layer. A method of forming a metal electrode, comprising the step of selectively depositing a metal on the layer of the compound semiconductor. 2. The step of forming the ultrathin layer protective film on the surface of the compound semiconductor after removing the oxide film on the surface of the compound semiconductor layer according to claim 1, 1. A method for forming a metal electrode, which comprises a step of immersing in a metal solution and a step of performing heat treatment under atmospheric pressure or reduced pressure. 3. The method for forming a metal electrode according to claim 1, wherein the step of removing the ultrathin layer protective film in a desired region by irradiation with the energy beam is performed by maskless irradiation with a charged particle beam such as electrons or ions. ..