JP2000183022A - Manufacture of compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely remove an oxide film on the surface of an AlGaAs layer generated by a selective etching, in a recess-gate type FET. SOLUTION: In a process for manufacturing a recess-gate type FET, a recess etching process (S105) subjects it to an aqueous solution containing aqueous ammonia for selective etching with GaAs in wet-etching. An aluminum oxide film generated on the surface of an AlGaAs layer at the lower part GaAs in the recess etching process is removed (S106) in an aqueous phosphate. The temperature of the aqueous phosphate is kept at 30 deg. or below and only an oxide film is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a method for manufacturing a recess gate type FET.

[0002]

2. Description of the Related Art Conventionally, GaAs / AlGaAs H
2. Description of the Related Art A recess gate structure is used in a compound semiconductor device such as an EMT (high electron mobility transistor).

An FET having a recess gate structure is usually made of GaAs.
The s / AlGaAs layer is selectively etched by using only an aqueous solution containing phosphoric acid and hydrogen peroxide to form a recess (groove), and is formed on the surface of the AlGaAs layer in the recess etching step. The oxide film such as alumina was removed using HF.

[0004]

However, GaAs is selectively used by using an aqueous solution containing a phosphoric acid solution and a hydrogen peroxide solution.
When etching only the s layer, since the etching rates of phosphoric acid water and hydrogen peroxide water for GaAs and AlGaAs are almost equal, it is necessary to remove only the GaAs layer by strictly controlling the etching time. There was a problem that etching was difficult.

In the step of removing the oxide film formed on the surface of the AlGaAs layer by HF, not only the oxide film but also the protective film (SiN) located on the side surface of the recess is etched, and the recess width is reduced. Problems such as enlargement and partial peeling of the resist occur, and there is a problem that electrical characteristics such as mutual conductance are lowered.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and performs a selective etching (recess etching) of GaAs easily and surely, and forms a selective etching process on the surface of an AlGaAs layer. An object of the present invention is to provide a method capable of manufacturing a compound semiconductor device having excellent electrical characteristics by reliably removing only an oxide film.

[0007]

In order to achieve the above object, the present invention provides a method of manufacturing a recess gate type compound semiconductor device having an AlGaAs layer and a GaAs layer laminated on a substrate, the method including an aqueous ammonia. A selective etching process for selectively etching the GaAs layer using an aqueous solution, and an oxide film for selectively removing an oxide film formed on the surface of the AlGaAs layer in the process of the selective etching process using a phosphoric acid solution It is characterized by including a removal process. An aqueous solution (NH ₄ OH + H ₂ O ₂ ) containing aqueous ammonia and hydrogen peroxide etches GaAs, whereas etching of AlGaAs is prevented by an oxide film formed on the surface. Therefore, by using an aqueous solution containing aqueous ammonia in the selective etching process (recess etching process),
Only the s layer can be selectively etched easily and reliably. Then, after the selective etching process, wet etching is performed using phosphoric acid water (H ₃ PO ₄ ), so that a protective film such as SiN is not etched.
Only the oxide film formed on the surface of GaAs can be removed. Since the hot phosphoric acid solution etches SiN and the like, the phosphoric acid solution used in the oxide film removal process is S
The temperature is kept low enough not to etch iN or the like.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows GaAs / GaAs in this embodiment.
The manufacturing process of AlGaAs HEMT is shown. An AlGaAs layer, a GaAs layer, a GaAs contact layer, and the like are sequentially epitaxially grown on the substrate (S101).
After element isolation (S102), a SiN spacer is formed (S103) to form a source / drain (S10).
4).

FIG. 2 is a sectional view of the device obtained in the steps up to S104. Semi-insulating GaAs substrate 1
A GaAs buffer layer 12, an AlGaAs electron supply layer 14, and a GaAs contact layer 16 are formed by epitaxial growth on the SiN spacer 18 and the source 2
0, a drain (AuGe / Ni / Au) 22 is formed.

Returning to FIG. 1, after forming the source / drain, a resist is laminated, and selective etching (recess etching) of the GaAs layer is performed using this resist as a mask (S105). One of the features of this embodiment is that an aqueous solution containing aqueous ammonia (aqueous ammonia and hydrogen peroxide) is used in this selective etching (recess etching), and an aqueous solution containing aqueous ammonia (aqueous ammonia and hydrogen peroxide) is used. The etching rate of GaAs in water is about 20
By utilizing the fact that the etching rate of AlGaAs is extremely slow at about 1 nm / min, whereas it is 0 nm / min, it is possible to easily selectively etch only the GaAs layer.

FIG. 3 is a sectional view showing a case where selective etching (recess etching) is performed with an aqueous solution containing ammonia water (aqueous ammonia and hydrogen peroxide). A photoresist 23 is laminated, and only the GaAs contact layer 16 is etched by wet etching using an aqueous solution containing aqueous ammonia to form a recess 24. At the time of this selective etching (recess etching),
An oxide film 26 of alumina or the like is formed on the surface of the AlGaAs electron supply layer 14 (the aluminum oxide film 26 is hardly etched by an aqueous solution containing ammonia water, and thus can be selectively etched).

Returning to FIG. 1, after selective etching (recess etching) is performed to form a recess, AlGaAs is formed.
The oxide film 26 formed on the surface of the s electron supply layer 14 is removed (S106). The removal of the oxide film 26 is performed by wet etching using phosphoric acid water. The condition of the wet etching is to maintain the temperature of the phosphoric acid water at a low temperature of 30 degrees or less. The hot phosphoric acid water exceeding 30 degrees is not only the oxide film 26 but also the SiN spacer 1 remaining on the side surface of the recess.
8 is also side-etched. In this embodiment, only the oxide film 26 can be removed by performing etching at a temperature of 20 to 25 degrees for 10 minutes.

After removing the oxide film, a gate is formed by vapor deposition in the recess (S107), the resist is lifted off, an interlayer insulating film is formed (S108), and an upper wiring (S109) is performed, thereby completing the HEMT manufacturing.

FIG. 4 is a cross-sectional view after the upper wiring is formed in S109. Gate 28 in recess 24
(Ti / Pt / Au) is formed. The protective film 30 is formed simultaneously with the formation of the interlayer insulating film in S108.

As described above, in the present embodiment, since the aqueous solution containing ammonia water (aqueous ammonia and hydrogen peroxide solution) is used in the selective etching (recess etching) process, the AlGaAs layer is laminated on the AlGaAs layer without being etched. Only the etched GaAs layer can be easily and reliably etched.

Since phosphoric acid water (non-hot phosphoric acid water) is used in the oxide film removing process, only the oxide film on the surface of the AlGaAs layer can be removed without affecting the recess structure.

In this embodiment, an aqueous solution containing aqueous ammonia (aqueous ammonia and aqueous hydrogen peroxide) is used in the selective etching. However, it is necessary to add citric acid to this aqueous solution to more effectively etch the GaAs layer. Are also suitable.

As an etching solution for removing an aluminum oxide film on the surface of the AlGaAs layer, an aqueous solution (H ₃ PO ₄ + H ₂ SO ₄ ) obtained by adding sulfuric acid to a phosphoric acid solution can be used.

In this embodiment, Si is used as a spacer.
Although N is used, it goes without saying that SiO ₂ may be used.

Furthermore, in the present embodiment, HEMT has been described as an example, but the method of the present invention is not limited to this, and all semiconductor devices (MESFET and MESFET) requiring an oxide film removing process after a selective etching process are required. PHEM
T, strain HEMT, etc.).

[0022]

As described above, according to the present invention,
Only the GaAs layer can be selectively etched easily and reliably, and the in-plane uniformity of the AlGaAs layer can be maintained. Further, according to the present invention, since only the oxide film on the surface of the AlGaAs layer can be reliably removed without affecting the peripheral structure, it is possible to obtain a compound semiconductor device having excellent properties such as mutual conductance and minimum noise figure. .

[Brief description of the drawings]

FIG. 1 is a manufacturing process flowchart of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the semiconductor device after a source / drain formation process in FIG. 1;

FIG. 3 is a sectional view of the semiconductor device after the recess etching process in FIG. 1;

FIG. 4 is a sectional view of the semiconductor device after a protective film forming process in FIG. 1;

[Explanation of symbols]

10 GaAs substrate, 12 GaAs buffer layer, 14
AlGaAs electron supply layer, 16 GaAs contact layer, 18 SiN spacer, 20 source, 22 drain, 24 recess, 26 oxide film, 28 gate.

Claims (1)

[Claims] 1. A method of manufacturing a recess gate type compound semiconductor device in which an AlGaAs layer and a GaAs layer are stacked on a substrate, wherein the selective etching process selectively etches the GaAs layer using an aqueous solution containing ammonia water. A process for selectively removing an oxide film formed on the surface of the AlGaAs layer in the course of the selective etching process using phosphoric acid water. Method.