JPH0260125A - semiconductor equipment - Google Patents

Abstract

PURPOSE:To prevent the contact resistance from being increased by the successive heat treatment process by a method wherein an opening is etched away using anisotropical etchant with face orientation dependence to form an ohmic electrode comprising a metallic layer on a wavy surface exposing (III) face to specific region. CONSTITUTION:A resist layer 3 is formed on e.g., a gallium.arsenic layer 1 forming the essential part of a semiconductor device and then an opening 4 is made in a source.drain electrode forming region by photolithography. Next, the opening 4 is etched away using anisotropical etchant with face dependence such as mixed solution, etc., of phosphoric acid and hydrogen peroxide solution to form wavy surface around 100Angstrom thick exposing (III) face to the source.drain electrode forming region. Then, a gold germanium layer around 400Angstrom thick, a nickel layer around 50Angstrom thick and a metal around 5000Angstrom thick are formed into one body to be heat-treated so that a three layered metallic layer 2 and the gallium.arsenic layer 1 may be alloyed to form an ohmic electrode. Through these procedures, the contact resistance can be prevented from being increased by the successive heat-treatment process.

Description

[Detailed Description of the Invention] [Summary] An object of the present invention is to provide a semiconductor device having an ohmic electrode with a reduced contact resistance and a highly conductive ohmic electrode that does not change due to continuous heat treatment. An ohmic electrode made of a metal layer formed on a semiconductor layer that is etched using an anisotropic etchant to expose the (111) plane and have a corrugated surface. be done.

[Industrial application field]

The present invention relates to a semiconductor device having an ohmic electrode with low contact resistance. In particular, the present invention relates to a semiconductor device having a metal electrode that is highly conductive to the source, drain, etc. of a field effect transistor made of a compound semiconductor.

[Conventional technology]

A method of forming an ohmic electrode with low contact resistance on a semiconductor layer is to form a metal layer on the surface of the semiconductor layer using a vapor deposition method, perform heat treatment, and alloy the vapor-deposited metal with the semiconductor. Widely used. When forming an ohmic electrode on a compound semiconductor layer, for example, a gallium arsenide layer, a three-layer metal layer in which gold germanium, nickel, and gold are sequentially laminated is generally used as a vapor-deposited metal.

The mechanism of alloying in this case is inferred as follows. Germanium enters the gallium vacancies of the gallium arsenide crystal as a donor, forming an n° layer with high carrier density. On the other hand, nickel reacts with gold and germanium to form a film-like nickel-gold-germanium alloy, which prevents the gold-germanium crystal grains from growing larger and appearing on the ohmic junction surface, and also prevents the alloy layer from growing deep (progressing). As a result, the alloy layer has a high carrier density n
It is connected to the gallium arsenide layer through the ° layer, forming a low-resistance ohmic electrode.

Other methods for reducing ohmic contact resistance include increasing the bonding area between the alloy layer and the semiconductor layer, and forming the edge of the bonding surface between the metal layer and the semiconductor layer into a tapered shape to prevent electric field concentration. There is.

Contact resistance may increase. The increase in contact resistance due to this high-temperature process is thought to be due to the fact that the alloying between the metal and the semiconductor further progresses in the depth direction due to the high-temperature process, and as a result, the n layer, which is effective for ohmic contact, disappears. Theoretically, if you back-calculate the effects of all heat treatment steps on ohmic contact before commercializing a semiconductor device and select the heat treatment conditions for the initial ohmic electrode formation so that the final ohmic contact is optimal, would be nice, but it is difficult to implement in reality.

An object of the present invention is to eliminate this drawback, and to provide a semiconductor device having a highly conductive ohmic electrode that does not change due to continuous heat treatment.

[Problem to be solved by the invention]

By the way, even if an ohmic bond is made using the optimal heat treatment conditions for alloying to form a low-resistance ohmic electrode, the ohmic bond will deteriorate due to the high temperature process that is carried out after that. Means] The above object is formed on a semiconductor layer (1) which is etched using an anisotropic etchant having plane orientation dependence to expose the (111) plane and have a corrugated surface. This is achieved by a semiconductor device having an ohmink electrode made of a metal layer (2).

[Effect]

It has been confirmed that when the interface between the metal layer and the semiconductor layer is flat, the ohmic contact resistance increases in the heat treatment step after forming the ohmic electrode. This is thought to be due to the fact that when the interface between the metal layer and the semiconductor layer is flat, alloying in the depth direction between the metal layer and the semiconductor layer during the heat treatment process tends to progress.8 Alloying progresses deeply. Then, the gold-gallium eutectic alloy eliminates the n'' layer formed by germanium entering the gallium vacancies as a donor, and also generates gallium vacancies to act as acceptors, thereby increasing the contact resistance. This is thought to be to increase the

The inventor of the present invention says that if the surface of the semiconductor layer is formed into a wave shape with uniform surface orientation and a metal layer is formed on top of the surface, alloying in the depth direction during the heat treatment process will be difficult to proceed. He discovered the laws of nature and skillfully applied them to realize the present invention. Forming the surface of the semiconductor layer into a wave shape having a uniform plane orientation is achieved by etching using an anisotropic etchant having plane orientation dependence to expose the (111) plane. If alloying is difficult to proceed in the depth direction, the n layer, which is effective for ohmic contact, will not disappear due to continuous heat treatment, and gallium vacancies will not be generated and act as acceptors.
Therefore, the ohmic contact resistance does not increase, and this has been experimentally confirmed.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, including a process for forming ohmic electrodes of the source and drain of a field effect transistor made of a compound semiconductor, to further clarify the structure of the present invention.

See Figures 2 and 3. FIG. 3 is an enlarged view of section A in FIG. 2.

For example, a gallium arsenide layer on which the main parts of a semiconductor device are formed
A resist layer 3 is formed thereon, and openings 4 are formed in the source/drain electrode formation regions using a photolithography method. Etching using etchant,
A wavy surface having a depth of about 100 mm with the (111) plane exposed is formed in the source/drain electrode formation region.

Using the deposition method shown in FIG. 1, a gold germanium layer is formed to a thickness of about 400 mm, then a nickel layer is formed to a thickness of approximately 50 mm, and then a gold layer is formed to a thickness of approximately 5,000 mm; A three-layer metal layer 2 of gold germanium/nickel/gold is formed by lift-off, and a heat treatment is performed at about 450° C. for about 2 minutes to form a three-layer metal layer 2 of gold germanium/nickel/gold and a gallium arsenide layer l. and forms an ohmic electrode.

〔Effect of the invention〕

As explained above, in a semiconductor device having an opaque electrode according to the present invention, etching is performed using an anisotropic etchant having surface orientation dependence.
) Since it has an ohmic electrode made of a metal layer formed on a semiconductor layer with a corrugated surface with an exposed surface, alloying in the depth direction is difficult to progress during the heat treatment process after forming the ohmic electrode. Therefore, contact resistance does not increase and high conductivity is maintained.

Refer to FIG. 4. To confirm the effect, an experiment was conducted to see how the ohmic contact resistance changes over time when heated and held at 350° C. after the alloying process for forming an ohmic electrode. The results are shown in Figure 4. In the case of the conventional ohmic electrode (indicated by the broken line), the contact resistance was approximately 3 after 60 minutes of heating.
On the other hand, in the case of the ohmic electrode according to the present invention (indicated by the solid line), there is almost no change, and it has been demonstrated that high conductivity is maintained even by continuous firing treatment after alloying. Ta.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of ohmic electrodes of the source and drain of a field effect transistor according to an embodiment of the present invention. FIG. 2 is a process diagram of the ohmic electrode. FIG. 3 is an enlarged view of section A in FIG. 2. FIG. 4 is a graph showing the change in contact resistance of the ohmic electrode with respect to heating time. Process diagram Fig. 2 1... Semiconductor layer, 2... Metal layer, 3... Resist layer, 4... Opening.

Claims (1)

[Claims] Formed on a semiconductor layer (1) that is etched using an anisotropic etchant having plane orientation dependence to expose the (111) plane and have a corrugated surface. Metal layer (
2) A semiconductor device characterized by having an ohmic electrode comprising: