JPH06151354A - Electrode formation method of semiconductor element - Google Patents

Abstract

PURPOSE:To prevent bored-up uneven parts produced by the heat treatment of an ohmic electrode. CONSTITUTION:An n<-> type buffer layer 2, an n-type action layer 3 and an n<++> highly conductive layer 4 are epitaxially grown continuously and sequentially on a GaAs semiinsulating substrate 1, an alloy of Au and Ge (ratio of Ge:12%) and individual metals of Ni and Au are laminated on them by a vacuum evaporation operation, and a metal film 6 to be used as an ohmic electrode later is formed. In addition, an insulating film 7, e.g. an SiN film, is deposited on its whole surface. After that, the Ge metal under the insulating film is diffused to the Gaps substrate by a thermal radiation annealing operation (RTP) for executing a rapid heat treatment by irradiating radiant light obtained by using a platinum wire, a lamp or the like, and the ohmic electrode is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device such as a gallium arsenide field effect transistor (hereinafter referred to as GaAsFE).
(Referred to as “T”).

[0002]

2. Description of the Related Art In recent years, GaAs FETs have been developed and put into practical use as high frequency devices as parts of BS converters and MICs.

FIG. 4 shows a plan view of one GaAsFET, and FIG. 5 shows a cross-sectional view of a GaAsFET ohmic electrode formed by a conventional general alloying method along a line AA 'in FIG. FIG. 6 shows a cross-sectional view of a post-process of forming an ohmic electrode of a GaAsFET by a conventional general alloying method, taken along the line AA ′ in FIG.

As shown in FIG. 4, a gate electrode 11 is formed between a source electrode 8 and a drain electrode 9, and one end of the gate electrode 11 is provided with a large pad portion 12 for leading out an electrode.

As shown in FIG. 5, after the buffer layer 2, the operating layer 3 and the high conductivity layer 4 are deposited on the semi-insulating substrate 1 (see FIG. 5).
(A)), forming a resist pattern with the photoresist 5 for forming an ohmic electrode (FIG. 5).
(B)).

Next, an alloy of Au and Ge, and metal films 6 of Ni and Au are sequentially deposited on the semiconductor substrate 1 by vacuum evaporation (FIG. 5C). After forming the metal film 6, unnecessary portions of the metal film other than the ohmic electrode formation region are removed by lift-off to form a desired electrode pattern (FIG. 5D).

After that, the semiconductor element is heat-treated (alloyed) at an arbitrary temperature to diffuse the Ge metal into the GaAs substrate to form an ohmic electrode, that is, an ohmic electrode (FIG. 6A). Then, the n ⁺⁺ type high conductivity layer 4 is etched to expose the n type operation layer 3. This portion is a so-called recess portion.

Subsequently, a resist pattern 10 is formed on the entire surface of the semiconductor substrate except the etched portion of the n ⁺⁺ type high conductivity layer (FIG. 6B).

Aluminum is laminated thereon by vacuum vapor deposition. Then, the resist pattern 10 and the aluminum on the resist pattern are separated by lift-off. By doing so, the gate electrode 11 made of aluminum is formed (FIG. 6C).

Thus, the GaAs FET is manufactured.

However, when the heat treatment as described above is performed, the alloy of Au and Ge causes a boring-up phenomenon, and unevenness appears on the ohmic electrode made of the alloy of Au and Ge.

Then, in the subsequent photolithography process, when the photoresist is exposed, the unevenness of the light prevents the light from wrapping around and leaving the photoresist at the necessary portions. Therefore, the photoresist is left on the ohmic electrode. There is a drawback that it is very difficult to form a fine pattern by using it.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, in which an alloy of Au and Ge forming an ohmic electrode, and Ni and Au metal films are sequentially vacuum-deposited. After that, the present invention provides a method for forming an electrode of a semiconductor element, which can prevent the unevenness of the boring-up generated by the heat treatment of the ohmic electrode by depositing an insulating film on the entire surface.

[0014]

A method for forming an electrode for a semiconductor device according to the present invention is a method for forming an electrode for a semiconductor device, wherein a metal ohmic electrode for the semiconductor device is formed on a semi-insulating substrate. A step of depositing a plurality of metals by vacuum evaporation, a step of removing the metal other than the ohmic electrode formation region, a step of depositing an insulating film on the ohmic electrode before heat treatment, and a heat treatment on the ohmic electrode. And a step of alloying.

In the method of forming an electrode of a semiconductor device having an ohmic electrode made of metal on a semi-insulating substrate, an insulating film is deposited on the ohmic electrode before heat treatment of the ohmic electrode.

[0016]

According to the present invention, by depositing the insulating film on the ohmic electrode before the heat treatment, it is possible to prevent the boring-up that occurs during the heat treatment and to eliminate the irregularities on the ohmic electrode.

[0017]

EXAMPLE A method for forming an electrode of a semiconductor device according to the present invention is GaA.
An example when applied to the production of an sFET will be described with reference to the drawings.

FIG. 1 is a sectional view of a GaAsFET in which the method for forming an electrode of a semiconductor device according to the present invention is applied to manufacture a GaAsFET.

On the GaAs semi-insulating substrate 1, an n ^-- type buffer layer 2, an n-type operating layer 3, and an n ⁺⁺ -type high-conductivity layer 4 are successively and epitaxially grown, and an alloy of Au and Ge is formed thereon. (Ge ratio 12%), Ni, and Au metals are laminated by vacuum vapor deposition to form an ohmic electrode later.
To form. Further, an insulating film, for example, a SiN film is deposited on the entire surface. After that, by an apparatus that performs rapid thermal processing by irradiating radiant light obtained using an incandescent wire, a lamp, or the like, that is, a thermal radiation annealing (RTP) apparatus
The Ge metal under the insulating film 7 is diffused into the GaAs substrate to form an ohmic electrode, that is, an ohmic electrode.

A method for manufacturing a GaAsFET when the above-described present invention is used for manufacturing a GaAsFET will be described below.

FIG. 2 shows a cross-sectional view of each ohmic electrode of the GaAsFET in each step before manufacturing, and FIG. 3 shows the GaAsFET.
7A to 7C are cross-sectional views of post-manufacturing steps of the ohmic electrode. The cross-sectional view is taken along the line AA ′ in FIG. 4 described above.

As shown in FIG. 2A, GaAs semi-insulating property
N on the substrate 1 having a thickness of 2 to 3 μm ^-Type buffer layer 2,
Carrier concentration 3.0 × 10¹⁷/ Cm³To 3.5 × 10
¹⁷/ Cm³, N-type operation with a thickness of 0.20 to 0.25 μm
Layer 3, carrier concentration 2.0 × 10¹⁸/ Cm³To 2.5
× 10¹⁸/ Cm³, N with a thickness of 0.5 μm⁺⁺Type high conductivity layer 4
Are successively epitaxially grown.

Then, PM is deposited on the n ⁺⁺ -type high-conductivity layer 4.
A MA type positive photoresist 5 is applied to a thickness of 0.8 μm, and then exposed and developed to form a resist pattern 5 for forming an ohmic electrode (FIG. 2B). A is formed on the entire surface of the semiconductor substrate on which the resist pattern 5 is formed (including on the resist pattern 5) in order from the lower layer.
A metal film 6 is formed by stacking alloys of u and Ge (Ge ratio 12%), Ni, and Au metals by vacuum deposition. The film thicknesses of the alloy of Au and Ge, Ni and Au are 800Å, 70Å and 1600Å, respectively (FIG. 2).
(C)).

After the vacuum deposition of the metal film 6, the resist pattern is dissolved using an organic solvent, and the unnecessary portion of the metal film other than the ohmic electrode formation region is peeled off. Forming a metal pattern (FIG. 2D). This ohmic electrode will later become a source electrode and a drain electrode.

Next, an insulating film 7 is deposited on the entire surface of the semiconductor substrate on which the metal pattern is formed by a plasma CVD device. The insulating film 7 is made of, for example, 1000 Å thick Si.
N film or the like.

After depositing the insulating film 7, by irradiating radiant light obtained by using an incandescent wire, a lamp or the like,
Equipment for rapid thermal processing, ie thermal radiation annealing (RTP)
Heat treatment is performed by the device.

For example, by performing a heat treatment (alloy) at 365 ° C. for 10 seconds in a nitrogen atmosphere using an infrared heating furnace device, the Ge metal under the insulating film 7 is diffused into the GaAs substrate and the ohmic property is obtained. An electrode having the, i.e., ohmic electrode (source electrode 8 and drain electrode 9) is formed (FIG. 3A).

Then, a resist pattern 10 is formed, the insulating film 7 between the source electrode 8 and the drain electrode 9 thereof is removed by etching, and the n ^{+ +} type high conductivity layer 4 is etched to obtain the n type. The operating layer 3 is exposed. This etching portion becomes a so-called recess portion (see FIG. 3).
(B)).

Aluminum is laminated thereon by vacuum vapor deposition. Then, the resist pattern 10 and the aluminum on the resist pattern are separated by lift-off. By doing so, the gate electrode 11 made of aluminum is formed (FIG. 3C).

Thus, the GaAs FET is manufactured.

As described above, by forming the insulating film on the ohmic electrode made of an alloy, it is possible to prevent the metal from boring up between Au and Ge during the heat treatment. The irregularities on the electrode made of the alloy can be removed.

Further, this makes it very easy to form a fine pattern using a photoresist.

Although the ohmic electrode formation of the GaAsFET has been shown in the above-mentioned embodiments, it can be applied to other GaAs elements such as HEMT and bipolar.

[0034]

As is clear from the above description, by depositing an insulating film on the ohmic electrode before heat treatment,
Since it is possible to prevent the alloying of Au and Ge from boring up caused by the heat treatment, the unevenness on the ohmic electrode is eliminated and a finer resist pattern can be formed, so that the reliability of the semiconductor element can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an ohmic electrode of the present invention.

FIG. 2 is a cross-sectional view of pre-manufacturing steps of the ohmic electrode of the present invention.

FIG. 3 is a post-process cross-sectional view of the ohmic electrode of the present invention.

FIG. 4 is a plan view of a conventional GaAs FET.

FIG. 5 is a cross sectional view of a conventional ohmic electrode before manufacturing.

FIG. 6 is a post-process cross-sectional view of a conventional ohmic electrode.

[Explanation of Codes] 1 GaAs semi-insulating substrate 2 n ⁻ type buffer layer 3 n type operating layer 4 n ⁺⁺ type high conductivity layer 5 positive type photoresist 6 metal film 7 insulating film 8 source electrode 9 drain electrode 10 resist pattern 11 gate electrode 12 pad portion

Claims (2)

[Claims] 1. A method of forming an ohmic electrode made of metal of a semiconductor element on a semi-insulating substrate, comprising: depositing a plurality of metals on the substrate by vacuum vapor deposition; It is characterized by comprising a step of removing the metal other than the electrode formation region, a step of depositing an insulating film on the ohmic electrode before heat treatment, and a step of heat treating the ohmic electrode to alloy it. Method for forming electrode of semiconductor device. 2. A method for forming an electrode of a semiconductor device, comprising an ohmic electrode made of metal on a semi-insulating substrate,
A method of forming an electrode of a semiconductor device, comprising depositing an insulating film on the ohmic electrode before heat treatment of the ohmic electrode.