JPH045834A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a T-shaped gate metal which does not cause a disconnection by a method wherein, when a gate metal is attached to a compound semiconductor device, a heat treatment is executed, a taper is formed only at a pattern by a second organic thin film, at the upper part, whose heat-treatment property is bad out of gate patterns by a first organic thin film and the second organic thin film and the pattern is expanded. CONSTITUTION:A resist thin film 2 which excels in a close contact property and a heat-resistance property is formed on an N-type active layer 1 of GaAs; a resist film 3 whose heat-resistant property is inferior to that of the film 2 is formed on it. Then, the resist films are simultaneously irradiated selectively with an electron beam; the film 3 is developed; an opening part 3a in a fine gate pattern is formed. After that, the layer 1 is wet-etched while an opening part 2a formed in the film 2 is used as a mask; an opening part 1a in an inverted mesa shape is formed; a heat treatment is executed; only the opening part 3a is expanded while a taper is being formed. Then, a gate metal 4 is applied to the whole surface while the opening part 1a is being filled; a photosensitive- resist thin film 5 in a prescribed shape is formed on it; a dry-etching operation is executed; only the metal 4 having a taper is left.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, particularly a compound semiconductor device.

Background of the Invention In recent years, compound semiconductor devices have been used as high-speed arithmetic elements in computers, satellite broadcasting and satellite communications, and high-frequency and low-frequency devices used in mobile communications such as car phones and mobile phones, due to the high mobility of compound semiconductors. It is expected to be used as a noise transmission/reception amplification device.

An example of a conventional method for manufacturing a compound semiconductor device will be described below with reference to FIG.

FIG. 2 shows the process of forming a gate metal of a conventional compound semiconductor device. In Figure 2 (a), I is an n-type active layer of gallium arsenide, and on top of this n-type active layer l is excellent adhesion with gallium arsenide, excellent heat resistance up to 300°C, and PM sensitive to electron beams and near ultraviolet rays
A GI resist thin film 2 is provided. This PMG
On the I resist thin film 2, there is provided a PMMA resist thin film 3 which has a heat resistance of only up to 150° C. and has excellent sensitivity to near ultraviolet light and can form fine patterns. Further, in FIG. 2(C), 4 is a gate metal for forming a Schottky gate with the n-type active layer 1 of gallium arsenide. In FIG. 2(d), 5 is a photosensitive resist thin film for processing the cross-sectional shape of the gate metal 4 into a T-shape.

Next, a gate metal forming process for a compound semiconductor device having one or more structures will be described.

First, in FIG. 2(a), a thin PMGI resist film 2 having excellent adhesion and heat resistance is formed on the n-type active layer l of gallium arsenide by spin coating and heat treatment at 250°C.

Next, a PMMA resist thin film 3 is formed on the PMCI resist thin film 2 by spin coating and heat treatment at 120°C. Next, the PMMA resist thin film 3 and PMG I
Simultaneous exposure is performed on the resist thin film 2 by selective irradiation using an electron beam. Next, the PMMA resist thin film 3
is developed to form a fine gate pattern opening 3a. Next, the PMCI resist thin film 2 is developed using the opening 3a of the PMMA resist thin film 3 as a mass to form an opening 2a having the same gate pattern. Next, in FIG. 2(b), using the opening 2a of the PMG T resist thin film 2 as a mask, the n of the gallium arsenide is removed.
The mold active layer 1 is wet-etched to form an opening 1a in the shape of an inverted mesa. Next, in FIG. 2(C), from above the PMMA resist thin film 3 using the electron beam evaporation method,
Gate metal 4 is deposited on the entire surface. Next, in FIG. 2(d), spin coating is performed on the gate metal 4 at 120°.
A photosensitive resist thin film 5 is formed by C heat treatment. Next, a remaining gate pattern larger than the opening 3a of the gate pattern of the PMMΔ resist thin film 3 is formed by selective exposure and development. Next, in FIG. 2(e), the gate metal 4 is dry etched using the gate remaining pattern of the photosensitive resist thin film 5 to form the same shape as the photosensitive resist thin film 5. Finally, in FIG. 2(f), the photosensitive resist thin film 5 and the PM
The MA resist thin film 3 and the PMG I resist thin film 2 are all dissolved in an organic solvent and removed.

However, in the above structure, as shown in FIG. 2(f), the photosensitive resist thin film 5, the PMMA resist thin film 3, and the PMCI resist thin film 2 are all dissolved in an organic solvent. When removing the PMMA resist thin film 2, the gate metal 4 on top of the PMMA resist thin film 2 is lifted on together with the PMMA resist thin film 2, resulting in a problem that a T-shaped gate structure cannot be formed.

The present invention solves these problems by wet-etching the n-type active layer of gallium arsenide to form an inverted mesa shape, and then heat-treating it to expand only the gate pattern of the PMMA resist thin film, thereby preventing disconnection. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can form a T-shaped gate structure without a gate structure.

Means for Solving the Problems In order to solve the problems, the present invention includes a step of forming a first organic thin film sensitive to electron beams or near ultraviolet light on a semiconductor substrate, and forming a first organic thin film on the first organic thin film. forming a second organic thin film that is sensitive to electron beams or near ultraviolet rays and has poorer heat resistance than the first organic thin film and undergoes shape change upon heat treatment; a step of performing selective irradiation or selective exposure to near ultraviolet rays; a step of forming a first opening in the second organic thin film by development; and a step of forming a first opening in the second organic thin film by development using the first opening as a mask. forming a second opening in the thin film; forming a third opening in the semiconductor substrate by etching using the second opening as a mask; and forming a slope in the first opening by heat treatment. a step of depositing a metal on the entire surface from above the second organic thin film; and a step of depositing a third film having photosensitivity and excellent corrosion resistance on the metal. a step of forming an organic thin film, a step of selectively exposing and developing the third organic thin film to form a remaining pattern larger than the first opening, and using the remaining pattern of the third organic thin film as a mask. The method includes etching the metal, and removing all the first, second, and third organic thin films using an organic solvent to form a T-shaped metal on the third opening. It is something.

Function: With this configuration, a T-shaped gate metal without disconnection can be formed, and the sheet resistance of the sheet metal can be significantly reduced.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings (FIG. 1). In the drawings, the same reference numerals as in the conventional example indicate the same members.

In the figure, members 1 to 5 are the same as those in the conventional example, so
The explanation will be omitted and the following will explain the gate metal formation process of compound semiconductor devices! I will explain.

First, in FIG. 1(a), a PMGI resist thin film 2 having excellent adhesion and heat resistance is formed on an n-type active layer 1 of gallium arsenide by spin coating and heat treatment at 250°C.

Next, PMG I is deposited on the PMG T resist thin film 2.
A PMMA resist thin film 3 having worse heat resistance than the resist thin film 2 is formed by spin coating and 120°C heat treatment. Next, the PMMA resist thin film 3 and the PMG I resist thin film 2 are simultaneously exposed by selective irradiation using an electron beam.

Next, the PMMA resist thin film 3 is developed to form a fine gate pattern opening 3a. Next, the PM
Using the opening 3a of the MA resist thin film 3 as a mask, the P
The MGI resist thin film 2 is developed to form an opening 2a having the same gate pattern. Next, in FIG. 1(b), using the opening 2a of the PMG I resist thin film 2 as a mask, the n-type active layer 1 of gallium arsenide is wet-etched to form an opening 1a in the shape of an inverted mesa. Next, in FIG. 1(C), heat treatment is performed at 200° C. so that only the opening 3a of the gate pattern of the PMMA resist thin film 3 is tapered or enlarged. Next, Figure 1 (d
), a gate metal 4 is deposited over the entire surface of the PMMA resist thin film 3 using an electron beam evaporation method. Next, in FIG. 1(e), a photosensitive resist thin film 5 having excellent corrosion resistance is formed on the gate metal 4 by spin coating and heat treatment at 120°C. Next, a remaining gate pattern larger than the opening 3a of the gate pattern of the PMMA resist thin film 3 is formed by selective exposure and development. Next, in FIG. 1(f), the gate metal 4 is dry-etched using the gate leaving pattern of the photosensitive resist thin film 5, and the photosensitive resist thin film 5 is etched by dry etching.
form the same shape as. Finally, in FIG. 1(g), the photosensitive resist thin film 5, PMMA resist thin film 3, and PMCI resist thin film 2 are completely dissolved in an organic solvent and removed, and the n-type active layer 1 of gallium arsenide is inverted. A T-shaped gate metal 4 is formed in the mesa-shaped opening 1a.

As described above, according to this embodiment, after the n-type active layer 1 of gallium arsenide is formed into an inverted mesa shape as shown in FIG.
By tapering the gate pattern of the resist thin film 3 and expanding the gate pattern, the gate metal 4 deposited on the entire surface is connected deep into the gate pattern without disconnection at the gate pattern portion, as shown in FIG. 1(d). . By preventing wire breakage in this way, after removing all the resist with an organic solvent as shown in FIG. A T-shaped gate metal 4 that can reduce resistance is formed.

In the embodiment, an n-type active layer l of gallium arsenide was used, but the active layer is not limited to gallium arsenide, and may be any semiconductor. HE using heterojunctions such as gallium arsenide/aluminum gallium arsenide
MT etc. can be considered. Alternatively, after forming the active layer in an inverted mesa shape, heat treatment is performed to make the PMMA resist thin film 3 taper, or heat treatment is first performed to make the PMMA resist thin film 3 taper, and then the active layer is formed in an inverted mesa shape. You may.

Effects of the Invention As described above, according to the present invention, heat treatment is applied to only the gate pattern of the upper second organic thin film, which has poor heat resistance, among the gate patterns of the first organic thin film and the second organic thin film. By tapering and widening the gate pattern, it is possible to form a T-shaped gate metal with no disconnection, and this T-shaped shape can significantly reduce the gate resistance of the gate metal, which has great practical effects. .

[Brief explanation of the drawing]

FIGS. 1(a) to (g) are process diagrams for forming gate metal of a compound semiconductor device according to an embodiment of the present invention, and FIG. 2(a) is
-(f) are process diagrams for forming gate metal of a conventional compound semiconductor device. DESCRIPTION OF SYMBOLS 1... N-type active layer of gallium arsenide, 1a... Opening part, 2... PMG I resist thin film, 2a... Opening part, 3... PMMA resist thin film, 3a... Opening part,
4...Gate metal, 5...Photosensitive resist thin film.

Claims (1)

[Claims] 1. forming a first organic thin film sensitive to electron beams or near ultraviolet rays on a semiconductor substrate; and forming a first organic thin film sensitive to electron beams or near ultraviolet rays on the first organic thin film; a step of forming a second organic thin film that is less heat resistant and undergoes shape change upon heat treatment, and a step of selectively irradiating the second organic thin film and the first organic thin film with an electron beam or selectively exposing near ultraviolet rays. a step of forming a first opening in the second organic thin film by development; and a step of forming a second opening in the first organic thin film by development using the first opening as a mask. forming a third opening in the semiconductor substrate by etching using the second opening as a mask;
a step of enlarging the opening of the second organic thin film, a step of evaporating a metal over the entire surface of the second organic thin film, and forming a third organic thin film having photosensitivity and excellent corrosion resistance on the metal. a step of selectively exposing and developing the third organic thin film to form a remaining pattern larger than the first opening; and etching the metal using the remaining pattern of the third organic thin film as a mask. the first step;
A method for manufacturing a semiconductor device comprising the step of removing all the second and third organic thin films using an organic solvent and forming a T-shaped metal over the third opening.