JPS6395620A - Forming method for ohmic electrode - Google Patents

Abstract

PURPOSE:To improve an ohmic characteristic and a yield rate by a method wherein an NiGe alloy is evaporated on a GaAs substrate, a heat treatment of a specific temperature is then applied in a reducing atmosphere or an inactive atmosphere to form an alloy layer and Au is evaporated on the alloy layer. CONSTITUTION:After an active layer 2 is formed on a semi-insulative GaAs substrate 1, photoengraving is conducted to form a first photoresist 3. Next, an NiGe alloy layer 4 is formed by evaporation. By melting the first photoresist 3 subsequently, an unnecessary pattern is removed, while a desired pattern is formed. Next, a heat treatment of a specific temperature of 360 deg.C-450 deg.C is applied to form an alloy layer 5 in a reducing atmosphere, e.g. H2, or in an inactive gas atmosphere, e.g. N2. Then, a second photoresist 6 is formed in a part other than on the alloy layer 5. An Au layer 7 is formed by evaporation on the alloy layer 5. By removing the second photoresist 6 subsequently, an unnecessary pattern is removed, and thus a desired ohmic electrode is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming an ohmic electrode of a compound semiconductor.

[Conventional technology]

FIG. 2 is a cross-sectional view for explaining a conventional ohmic electrode forming method. In Fig. 2, 1 is a semi-insulating gallium arsenide (hereinafter referred to as rGaAsJ) substrate, 2 is an active layer, 3 is a photoresist formed by photolithography, and 4 is an A
5 is a Ni layer, 6 is an Au layer, and 7 is an alloy layer formed after heat treatment.

Next, a method for forming an ohmic electrode will be explained using FIG. 2.

First, an active layer 2 is formed on a GaAs substrate 1, and then photolithography is applied to form a photoresist 3 for forming an ohmic electrode (FIG. 2(a)).

Next, using a vapor deposition method, an Au08 layer 4. Ni layer 5, Au
Layer 6 is formed continuously (FIG. 2(b)).

Next, unnecessary metal and photoresist are removed by immersing in acetone and removing the resist, thereby forming a desired pattern (FIG. 2(C)).

Next, in a reducing atmosphere such as N2 or in an inert gas atmosphere such as N2, for example at 360°C to 450°C.
c. Heat treatment is performed for 1 to 3 minutes to form an alloy layer 7 and obtain an ohmic electrode (FIG. 2(d)).

・ [Problem to be solved by the invention] Since the conventional ohmic electrode forming method is configured as described above, when the alloying reaction progresses through heat treatment, the outermost gold is affected, and the surface becomes Roughness or ball-up may occur, resulting in masking or mask misalignment during post-process photolithography.
Alternatively, there is a problem that it becomes a cause of poor appearance after the process is completed.

The present invention has been made in view of these points, and its purpose is to be able to obtain a flat surface without surface roughness or ball-up, and to obtain good ohmic characteristics. An object of the present invention is to provide a method for forming an ohmic electrode.

[Means for solving problems]

In order to achieve such an object, the present invention uses GaAs having an active layer in the process of forming an ohmic electrode.
Step of vapor depositing NiGe alloy on the substrate and 360℃~4
This method includes a step of forming an alloy layer by performing heat treatment at 50° C. in a reducing atmosphere or an inert atmosphere, and a step of vapor depositing Au on the alloy layer.

[Effect]

In the present invention, surface roughness in the uppermost Au layer is prevented, and a good ohmic electrode is formed.

〔Example〕

FIG. 1 is a cross-sectional view for explaining one embodiment of the ohmic electrode forming method according to the present invention. In Figure 1,
1 is a semi-insulating GaAs substrate, 2 is an active layer, 3 is a first photoresist formed by photolithography (hereinafter referred to as "first photoresist"), 4 is a NiGe layer formed by vapor deposition, 5
6 is the heat-treated alloy layer, 6 is the second photoresist (hereinafter referred to as "second photoresist"), and 7 is A formed by vapor deposition.
This is the U layer.

Next, this method will be explained using FIG. 1.

After forming an active layer 2 on a semi-insulating GaAs substrate 1, photolithography is performed to form a first photoresist 3 (see FIG. 1(a)).
)).

Next, a NiGe alloy layer 4 is deposited using a vapor deposition method (FIG. 1(b)).

Next, by dipping in acetone and dissolving the first photoresist 3, unnecessary patterns are removed and a desired pattern is formed (FIG. 1(C)).

Next, heat treatment is performed at, for example, 360 DEG C. to 450 DEG C. in a reducing atmosphere such as H2 or an inert gas atmosphere such as N2 to form the alloy layer 5 (FIG. 1(d)).

Next, a second photoresist 6 is formed on areas other than the alloy layer 5 (FIG. 1(e)).

Next, an Au layer 7 is deposited on the alloy layer 5 using a vapor deposition method (FIG. 1(f)).

Next, unnecessary patterns are removed by immersing in acetone and removing the second photoresist 6, thereby obtaining a desired ohmic electrode (FIG. 1 (g6)).

In the above embodiment, a semi-insulating GaAs substrate was used as the substrate 1, but a GaAs substrate using a shrimp layer may also be used, and the same effect can be obtained.

〔Effect of the invention〕

As explained above, in the present invention, after alloying treatment, Au
By forming the layers separately, it is possible to prevent the surface of the top layer of Au5 from becoming rough and prevent ball-up from occurring, so it is possible to obtain good ohmic characteristics and to avoid negative effects in the photolithography process in the subsequent process. This has the effect of significantly improving yield without causing any adverse effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining an embodiment of the ohmic electrode forming method according to the present invention, and FIG. 2 is a sectional view for explaining a conventional ohmic electrode forming method. ■...GaAs substrate, 2...active layer, 3...first
Photoresist, 4... NiGe layer, 5... Alloy layer,
6... Second photoresist, 7... Au layer.

Claims (1)

[Claims] a step of vapor depositing a NiGe alloy on a GaAs substrate having an active layer; a step of performing heat treatment at 360° C. to 450° C. in a reducing atmosphere or an inert atmosphere to form an alloy layer;
An ohmic electrode forming method comprising the step of vapor depositing Au on the alloy layer.