JPH0997913A - Method for manufacturing compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove simply S left on GaAs generated at the time of dry etching and form a gate electrode having stably excellent Schottky characteristics. SOLUTION: After a silicon oxide film 3 is formed on a GaAs substrate 1 having an operation layer 2, the silicon oxide film 3 is dry-etched using SF6 gas. At this time, residual sulfur 6 remains on a face of GaAs. Next, after photoresist 4-1 is removed and it is soaked in an aqueous solution of hydrochloric acid, it is baked at a high temperature of 300 or more to less than 600 deg.C under H2 gas atmosphere to remove the residual sulfur 6. A gate electrode is formed and a source.drain electrode is formed to obtain a semiconductor device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a method for manufacturing a gate electrode of MESFET.

[0002]

2. Description of the Related Art A Schottky barrier gate field effect transistor (MESFET) using a group III-V compound semiconductor such as GaAs (gallium arsenide).
Is a structure having a gate electrode with a Schottky junction formed by contact between a metal and a semiconductor, and it is often used as a low noise amplification element for microwave and millimeter wave band and a high output amplification element by utilizing excellent high frequency characteristics. ing.

What is important as the gate electrode of the Schottky junction that controls the characteristics and reliability of the MESFET is φ.
_B (the height of the Schottky barrier seen from the metal side) is stable and increases. In the case of an ideal contact between a metal and a semiconductor, φ _B is given by the difference between the work relationship φ _{m of the} metal and the electron affinity χ of the semiconductor (φ _B = φ _m −χ). Actually, the Fermi level on the surface is pinned by many interface levels existing on the compound semiconductor surface,
φ _B is determined.

Therefore, in order to stabilize and increase φ _B , it is desirable that the surface of the semiconductor is as clean as possible and the interface state density is low.

On the other hand, as the gate electrode material, the specific resistance is small, the adhesion to the semiconductor substrate is good, the stress is low,
A heat resistant metal is desirable. A gate electrode material that has been often used conventionally is aluminum (Al). A
This is because l has a small specific resistance and a submicron-sized gate electrode can be easily formed by a lift-off method using electron beam evaporation. However, since Al easily causes electromigration, the reliability is remarkably lowered as the dimension becomes smaller. In recent years, as a highly reliable gate metal material alternative to Al, tungsten (W), molybdenum (Mo), tungsten silicide (WSi _x N _y) a refractory metal-based conductive film such as have been used. This refractory metal-based conductive film has the following advantages. First, since it has good heat resistance, a high temperature of 400 to 800 ° C. can be used in the MESFET manufacturing process. Next, since fine processing can be performed by dry etching using a halogen gas, a submicron-sized gate electrode can be formed. Third, it is highly reliable.

GaAsME using a refractory metal-based conductive film
There are two examples of conventional methods for manufacturing SFETs.

4 (a) to 4 (d) are sectional views showing the first example in the order of steps.

First, as shown in FIG. 4 (a), after an operating layer 2 (channel layer) is formed on a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation,
400 nm thick silicon oxide film 3 formed by LPCVD
Is formed, a photoresist mask 4-1 is formed by using a lithography technique, and the silicon oxide film 3 is selectively dry-etched using SF ₆ gas to form an opening 5 for forming a gate electrode.

Next, as shown in FIG. 4B, a photoresist mask 4--using a gas containing oxygen (O ₂ ) in a barrel-type or parallel-plate-type reaction vessel for generating plasma discharge. 1 is peeled off. Further, as a method for removing the photoresist with a solution, a method of immersing in a mixed solution of dichlorobenzenephenol and alkylbenzenesulfonic acid at high temperature (120 ° C.) and then sequentially immersing in methyl ethyl ketone and alcohol (hereinafter, this is referred to as high temperature organic It is described as a photoresist stripping method using an agent).

Then, as shown in FIG. 4 (c), it is immersed in a hydrochloric acid aqueous solution (the ratio of HCl and H ₂ O is 1: 1) to form GaA.
s After removing the oxide on the surface and the fluoride remaining during the dry etching, a 200 nm-thick WSi film that becomes a part of the gate electrode is formed on the surface of the silicon oxide film including the opening.
After forming the _x (X = 2) film 7 by a vapor deposition method or a sputtering method, a titanium nitride (TiN) film having a thickness of 100 nm, a platinum (Pt) film having a thickness of 200 nm, and a gold (A) having a thickness of 700 nm are formed.
u) A film 8 (hereinafter referred to as a TiN-Pt-Au film) is formed by sequentially forming films by vapor deposition or sputtering.

Next, a photoresist mask (not shown) is formed on the TiN-Pt-Au film 8 by a lithography technique.
And forming TiN-Pt-Au by the ion milling method.
After etching the film 8, a reactive ion etching method using a mixed gas of SF ₆ and CF ₄ (hereinafter referred to as RIE)
The WSi _x film 7 is dry-etched by
As shown in (d), the gate electrode 9-1 is obtained.

Then, as shown in FIG. 4 (e), the silicon oxide film 2 at the position where the source electrode and the drain electrode are formed is selectively removed, and the source electrode 10 is formed by the vapor deposition method or the sputtering method. Then, the drain electrode 11 is selectively formed to complete the semiconductor device element portion.

Next, a second example of the conventional manufacturing method will be described with reference to FIGS.

First, as shown in FIG. 5A, the operation layer 2
After the WSi _x film 7 which will be a part of the gate electrode is formed on the GaAs substrate 1 on which is formed by the evaporation method or the sputtering method, the TiN-Pt-Au film 8 is formed by the evaporation method or the sputtering method. To do.

Next, as shown in FIG. 5 (b), TiN-
A photoresist mask 4-2 is formed on the Pt-Au film 8 by a lithography technique, and T is formed by an ion milling method.
After etching the iN-Pt-Au film 8, the WSi _x film 7 is dry-etched by reactive ion etching using SF ₆ gas.

Next, as shown in FIG. 5C, the photoresist mask 4-2 is removed by an ashing method using O ₂ gas or a peeling method using a high temperature organic agent to obtain a gate electrode 9-2.

Next, as shown in FIG. 4D, the GaA was immersed in a hydrochloric acid aqueous solution (the ratio of HCl and H ₂ O was 1: 1).
After removing the oxide on the s surface and the fluoride remaining at the time of dry etching, the insulating film 12 is formed on the entire surface including the gate electrode 9-2 and GaAs.

Then, as shown in FIG. 5 (e), the insulating film 12 located where the source electrode and the drain electrode are to be formed is selectively removed, and the source electrode 10 and the source electrode 10 are formed by the vapor deposition method or the sputtering method. The drain electrode 11 is selectively formed to complete the semiconductor device element portion.

[0019]

In the first example of the above-described two conventional methods for manufacturing a compound semiconductor device, SF ₆ gas is used when dry etching the silicon oxide film to form the gate electrode opening. Since it is used, there is a problem that residual sulfur 6 (residue of sulfur or its compound) exists on the GaAs surface of the gate electrode opening. Similarly, in the second example of the conventional manufacturing method, since the WSi _x film is dry-etched using SF ₆ gas, there is a problem that residual sulfur 6 remains on the GaAs surface. When S remains on the GaAs surface, GaAs is doped with S, and φ _B between the gate metal and GaAs decreases, so that the Schottky characteristic deteriorates and the FET characteristic deteriorates. This problem is already known,
Autumn 1994 55th Annual Meeting of the Japan Society of Applied Physics 20p
-V-9 "Influence of process contamination on GaAs MESFET characteristics (2) -gate processing gas" (Proceedings of the same lecture 1
100 pages).

It has been revealed by X-ray photoelectron spectroscopy (XPS) analysis that S remains on the GaAs surface after the silicon oxide film is dry-etched using SF ₆ gas. GaA after dry etching after photoresist removal with high temperature organic agent and immersion treatment with hydrochloric acid solution
An energy spectrum graph of the s surface by XPS analysis is shown in FIG. FIG. 6B is a graph showing the bonding state of S. The solid line shows the actual measurement curve after the immersion treatment, and the alternate long and short dash line shows the actual measurement curve before dry etching. A peak showing the 2p bond of S is observed, which shows that S cannot be removed by photoresist stripping and treatment with an aqueous hydrochloric acid solution. Also,
FIG. 6A is a graph showing the bonding state of As, the solid line is the measured curve after dry etching, and the broken line is the curve estimated for analysis corresponding to each bonding state. As-S bonds were observed, and S remaining after dry etching was A
is associated with s. By the same analysis, it is known that S is not removed even if the ashing method using O ₂ gas is performed after the dry etching.

It is also possible to use only CHF ₃ or CF ₄ gas in dry etching without using SF ₆ gas. In this case, however, the etching damage to the GaAs substrate is more than that in the case of SF ₆ gas. Also becomes large, and there arises a problem that desired FET characteristics cannot be stably obtained.

Therefore, an object of the present invention is to provide a method for manufacturing a compound semiconductor, which can remove residual sulfur generated during dry etching for forming a gate electrode and reduce dry etching damage.

[0023]

According to a first method of manufacturing a compound semiconductor device of the present invention, an active layer is formed on a compound semiconductor substrate, a first film is formed, and dry etching is performed using a gas containing at least sulfur. A first step of selectively removing the first film to expose the surface of the operating layer;
A second step of performing a heat treatment in a gas atmosphere containing at least hydrogen to remove residual sulfur from the exposed surface of the operating layer, and a Schottky of a gate electrode forming a Schottky junction with the operating layer. The barrier height is prevented from being lowered by residual sulfur. If the compound semiconductor substrate is a GaAs substrate, 300 ° C to 600 ° C
The heat treatment may be performed for less than.

According to a second method of manufacturing a compound semiconductor device of the present invention, an active layer is formed on a compound semiconductor substrate to form a first film, and the first film is selected by dry etching using a gas containing at least sulfur. Of the residual sulfur from the exposed surface of the operating layer by exposing the exposed surface of the operating layer to plasma by a plasma discharge of a gas containing at least hydrogen after the first step of removing the residual sulfur from the exposed surface of the operating layer. And a second step for preventing the Schottky barrier height of the gate electrode forming a Schottky junction with the operating layer from being lowered by residual sulfur. A GaAs substrate can be used as the compound semiconductor substrate.

In the first and second compound semiconductor manufacturing methods, an insulating film may be formed as the first film, and after the second step, the second film forming a Schottky junction with the operating layer may be deposited. In this case, a film made of a refractory metal or its compound can be used as the second film.

Further, a conductive film which forms a Schottky junction with the operating layer can be formed as the first film. in this case,
A film made of a refractory metal or its compound can be used as the conductive film. In all of the above cases, dry etching using SF ₆ gas can be performed.

Heat treatment in an atmosphere containing hydrogen or exposure to plasma by plasma discharge of a gas containing hydrogen removes residual sulfur in the operating layer, so that adverse effects on the gate electrode can be avoided.

[0028]

Embodiments of the present invention will now be described with reference to the drawings. 1A to 1E are cross-sectional views of a semiconductor chip shown in the order of steps for explaining the first embodiment of the present invention.

First, as shown in FIG. 1A, an operating layer 2 is formed on the surface of a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation, and then a 400 nm thick silicon oxide film 3 is formed by LPCVD. A photoresist mask 4-1 is formed by using a lithographic technique.
Is formed, and the silicon oxide film 3 is selectively dry-etched (reactive ion etching) using SF ₆ gas,
An opening 5 for forming a gate electrode is formed. At this time, Ga
Residual sulfur 6 (meaning residue consisting of sulfur or its compound) remains on the As surface. A silicon nitride (SiN _x ) film or a silicon nitride oxide (SiO _x N _y ) film may be used instead of the silicon oxide film 3.

Next, as shown in FIG. 1B, an ashing method using a gas containing oxygen (O ₂ ) or a high temperature ( After immersing in a mixed solution of dichlorobenzenephenol and alkylbenzenesulfonic acid (120 ° C.),
After removing the photoresist mask 5 by a method of sequentially immersing in methyl ethyl ketone and alcohol, it is immersed in a hydrochloric acid aqueous solution (the ratio of HCl and H ₂ O is, for example, 1: 1) to remove the oxide on the GaAs surface and dry etching. After removing the residual fluoride, it is heated in an atmosphere of H ₂ gas to 30
A high temperature baking process (heat treatment) is performed at 0 ° C. or higher and lower than 600 ° C., for example, 400 ° C. for 30 minutes. By the high temperature baking in this H ₂ gas atmosphere, the residual sulfur 6 becomes H ₂ S and is vaporized and removed. When H ₂ gas was not introduced, S was not removed at 300 ° C or higher and lower than 600 ° C, and S was removed by the treatment at 600 ° C or higher.
Also volatilizes at the same time and the stoichiometry of the GaAs surface changes. Also, in the H ₂ gas atmosphere, 300
Residual sulfur is not completely removed at temperatures lower than 600 ° C., and stoichiometry of the GaAs surface changes at temperatures of 600 ° C. or higher. That is, in the high temperature baking in the H ₂ atmosphere of 300 ° C. or more and less than 600 ° C., the residual sulfur can be removed without changing the stoichiometry of the GaAs surface. Thus, a clean GaAs surface can be obtained without forming pits.

Then, as shown in FIG. 1C, a WSi _x (x = 2) film 7 having a thickness of 200 nm, which is a part of the gate electrode, is formed on the surface of the silicon oxide film including the opening by a vapor deposition method and a sputtering method. After that, a 100-nm-thick titanium nitride (TiN) film, a 200-nm-thick platinum (Pt) film, and a 700-nm-thick gold (Au) film are sequentially formed by vapor deposition or sputtering. A film (hereinafter referred to as a TiN-Pt-Au film) 8 is formed.

Next, a photoresist mask (not shown) is formed on the TiN-Pt-Au film 8 by a lithography technique, and the TiN-Pt-Au film 8 is formed by an ion milling method.
After the etching, the WSi _x film 7 is dry-etched by a reactive ion etching method using a mixed gas of SF ₆ and CF ₄ (hereinafter abbreviated as RIE), and as shown in FIG. 9-1 is obtained.

Then, as shown in FIG. 1 (e), the silicon oxide film 3 located at the place where the source electrode and the drain electrode are formed is selectively removed, and the source electrode 10 is formed by the vapor deposition method or the sputtering method. Then, the drain electrode 11 is selectively formed to complete the semiconductor device element portion.

It should be noted that the high temperature baking under H ₂ atmosphere causes S
It has been proved by XPS analysis that can be removed. After dry etching, the photoresist was stripped off with a high temperature organic agent, and then water immersion treatment was performed with a hydrochloric acid aqueous solution, and then H
₂ XPS on GaAs surface after high temperature baking in atmosphere
A graph of the energy spectrum by analysis is shown in FIG. FIG. 2A is a graph showing the binding state of As, in which the solid line is the actual measurement curve, and the broken line is As ₂ O ₃ estimated for analysis.
It is a curve of a binding state of As-As and Ga-As. FIG.
(B) shows the bonded state of Ga, the solid line represents the measured curve before dry etching, the dashed line represents the measured curve after the H ₂ treatment described above, and the broken line represents the difference between the two. As shown in FIG. 6, peaks showing 2p binding of S and As-
No peak showing S-bonding is seen, indicating that S has been removed.

Since the opening for forming the gate electrode is formed by reactive ion etching with SF ₆ , damage to the active layer is small, and residual sulfur is hardly changed by heat treatment in H ₂ gas. Since the WSi _x film forming Schottky bonds is deposited after the removal, a gate electrode having a low interface state density can be stably formed. Therefore,
It is possible to form a MESFET having a small gate leakage current and a good mutual conductance.

Next, regarding the second embodiment of the present invention,
Similar to the first embodiment, description will be made with reference to FIG.

First, as shown in FIG. 1A, an operating layer 2 is formed on a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation, and then a silicon oxide film 3 having a thickness of 400 nm is formed by LPCVD. A film is formed, a photoresist mask 4-1 is formed by using a lithography technique, and the silicon oxide film 3 is selectively dry-etched (reactive ion etching) by using SF ₆ gas to form a gate opening 5. At this time, residual sulfur 6 remains on the GaAs surface.

Next, as shown in FIG. 1B, the photoresist mask is removed by an ashing method or a stripping method using a high-temperature organic agent, and then immersed in a hydrochloric acid aqueous solution to form GaA.
s After removing oxides on the surface and fluorides remaining during dry etching, hydrogen (H ₂ ) in a barrel-type, parallel plate-type, or electron cyclotron resonance-type (ECR) -type plasma discharge generating reactor. Plasma is irradiated using gas. For example, in the ECR plasma device,
ΜW power of ECR source 50W, pressure 0.13Pa,
The hydrogen flow rate is 10 sccm. At this time, hydrogen radicals generated in the plasma are adsorbed on the GaAs surface, and then the hydrogen radicals and residual sulfur 6 react with each other to become H ₂ S and volatilize, and the residual sulfur 6 is removed. Thus, a clean GaAs surface can be obtained without forming pits.

After that, the semiconductor device is obtained by using the same method as that of the first embodiment.

[0040] Although performing plasma irradiation with H ₂ gas after the photoresist mask is removed, after selectively dry etching the silicon oxide film 2 by using a SF ₆ gas, using H ₂ gas A method of performing plasma irradiation and then removing the photoresist mask may be used.

According to this embodiment, almost the same result as that of the first embodiment can be obtained.

FIGS. 3A to 3E are cross-sectional views of the semiconductor chip shown in the order of steps for explaining the third embodiment of the present invention.

First, as shown in FIG. 3A, the operation layer 2
A 200 nm-thick WSi _x film 7 which will be a part of a gate electrode is formed on the GaAs substrate 1 on which is formed by a vapor deposition method or a sputtering method, and then a TiN-Pt-Au film 8 is vapor-deposited or sputtered. Form by the method.

Next, as shown in FIG. 3B, TiN-
A photoresist mask 4-2 is formed on the Pt-Au film 8 by a lithography technique, and T is formed by an ion milling method.
After etching the iN-Pt-Au film 8, the WSi _x film 7 is dry-etched by reactive ion etching using SF ₆ gas. At this time, residual sulfur 6 remains on the GaAs surface.

Next, as shown in FIG. 3C, the photoresist mask 4-2 is removed by an ashing method using O ₂ gas or a stripping method using a high-temperature organic agent, and then immersed in an aqueous hydrochloric acid solution and dried. After removing the fluoride remaining at the time of etching, 300 or more and 600 or more in an atmosphere of H ₂ gas.
A high temperature baking process is performed at a temperature of less than 0 ° C., for example, 400 ° C. for 30 minutes. As a result, the residual sulfur 6 is removed without producing pits, and the cleaned GaAs surface and the gate electrode 9-2 are obtained.

Next, as shown in FIG. 3D, an insulating film 12 is formed on the gate electrode and GaAs.

Then, as shown in FIG. 3 (e), the insulating film 12 located at the place where the source electrode and the drain electrode are formed is selectively removed, and the source electrode 10 and the source electrode 10 are formed by the vapor deposition method or the sputtering method. The drain electrode 11 is selectively formed to complete the semiconductor device element portion.

The WSi _x film 7b of the gate electrode 9-2 and Ga
Since the residual sulfur is removed from the periphery of the Schottky junction with the As substrate 2, it is possible to avoid the reduction of the Schottky barrier height φ _B in the peripheral portion of the gate electrode. Therefore, compared to the second example of the conventional manufacturing method, the ME
The gate leakage current and transconductance of the SFET can be improved.

The third embodiment of the fourth embodiment of the present invention
This will be described with reference to FIG.

First, as shown in FIG. 3A, the operation layer 2
A 200 nm-thick WSi _x film 7 to be a part of a gate electrode is formed on the GaAs substrate 1 on which the Ti film has been formed by a vapor deposition method or a sputtering method, and then a TiN-Pt-Au film 8 is vapor-deposited or sputtered. To form.

Next, as shown in FIG. 3B, TiN-
A photoresist mask 4-2 is formed on the Pt-Au film 8 by a lithography technique, and T is formed by an ion milling method.
After etching the iN-Pt-Au film 8, the WSi _x film 7 is dry-etched by reactive ion etching using SF ₆ gas. At this time, residual sulfur 6 remains on the GaAs surface.

Next, as shown in FIG. 3C, after the photoresist mask 4-2 is removed by an ashing method using O ₂ gas or a high temperature organic agent, as in the second embodiment. Plasma irradiation is performed using hydrogen (H ₂ ) gas in a reaction vessel that generates plasma discharge, such as a barrel type, parallel plate type, or electron cyclotron resonance type (ECR) type. As a result, the residual sulfur 6 is removed without producing pits, and the cleaned GaAs surface and the gate electrode 9-2 are obtained.

After that, the semiconductor device is obtained by using the same method as that of the third embodiment.

According to this embodiment, almost the same result as that of the third embodiment can be obtained.

In this embodiment, plasma irradiation using H ₂ gas is performed after removing the photoresist mask. However, after dry etching the WSi _x film 7,
A method of performing plasma irradiation using _two gases and then removing the photoresist mask may be used.

Although the SF ₆ simple substance gas is used in the above first to fourth embodiments, other gases may be mixed. Further, any gas may be used as long as it is a compound or mixture containing S and F such as S ₂ F ₁₀ instead of SF ₆ .

The method of manufacturing a semiconductor device using a GaAs substrate has been described as an example.
A compound semiconductor substrate made of a V group, such as an InP substrate, may be used.

[0058]

According to the present invention described above, after the gate opening or the gate electrode is formed by dry etching using a gas containing sulfur such as SF6 gas, residual sulfur remaining in the operating layer on the compound semiconductor substrate is removed. By performing a high temperature bake treatment in an H2 gas atmosphere or performing plasma irradiation using H2 gas, it is possible to prevent the adverse effect of sulfur on the interface between the gate electrode and the semiconductor, so that the interface state density becomes low.
Moreover, dry etching damage can be reduced because ion etching using a gas containing carbon is not used. Therefore, it is possible to form a gate electrode having a stable φ _B and a gate electrode having a stable Schottky characteristic at all times.
This has the effect of improving the gate leakage current and transconductance of the ESFET.

Further, not only the residue does not exist at the interface between the gate electrode and the semiconductor, but also the change in the stoichiometry at the interface hardly occurs, so that the reliability of the semiconductor device is improved.

[Brief description of drawings]

FIG. 1 is a process sequence cross-sectional view divided into (a) to (e) for explaining a first embodiment and a second embodiment of the present invention.

FIG. 2 is a graph showing an energy spectrum by XPS analysis for explaining the first embodiment.

3A to 3E are cross-sectional views in order of the processes, which are divided into (a) to (e) for describing a third embodiment and a fourth embodiment of the present invention.

4A to 4E are cross-sectional views in order of the processes, which are divided into (a) to (e) for illustrating a first example of a conventional method for manufacturing a compound semiconductor device.

5A to 5E are cross-sectional views in order of the processes, which are divided into (a) to (e) for describing a second example of the conventional method for manufacturing a compound semiconductor device.

FIG. 6 is a graph showing an energy spectrum by XPS analysis for explaining a conventional example.

[Explanation of symbols]

1 GaAs substrate 2 operation layer (channel layer) 3 silicon oxide film 4-1 and 4-2 photoresist mask 5 opening 6 residual sulfur 7, 7a, 7b WSi _x film 8, 8a, 8b TiN-Pt-Au film 9- 1, 9-2 gate electrode 10 source electrode 11 drain electrode 12 insulating film

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 9447-4M H01L 29/80 F

Claims (9)

[Claims] 1. An active layer is formed on a compound semiconductor substrate to form a first layer.
Forming a film of 1) and selectively removing the first film by dry etching using a gas containing at least sulfur to expose the surface of the operating layer, and at least hydrogen after the first step. And a second step of removing residual sulfur from the exposed surface of the operating layer by performing heat treatment in a gas atmosphere containing the residual sulfur having a Schottky barrier height of a gate electrode forming a Schottky junction with the operating layer. A method for manufacturing a compound semiconductor device, comprising: 2. The method of manufacturing a compound semiconductor device according to claim 1, wherein the compound semiconductor substrate is a GaAs substrate, and heat treatment is performed at 300 ° C. or higher and lower than 600 ° C. 3. An active layer is formed on a compound semiconductor substrate to form a first layer.
Forming a film of 1) and selectively removing the first film by dry etching using a gas containing at least sulfur to expose the surface of the operating layer, and at least hydrogen after the first step. A second step of removing residual sulfur from the exposed surface of the operating layer by exposing the active layer to a plasma by plasma discharge, and the height of the Schottky barrier of the gate electrode forming a Schottky junction with the operating layer is increased. A method for manufacturing a compound semiconductor device, which is characterized by preventing deterioration due to residual sulfur. 4. The method of manufacturing a compound semiconductor device according to claim 3, wherein the compound semiconductor substrate is a GaAs substrate. 5. The method for manufacturing a compound semiconductor device according to claim 1, wherein an insulating film is formed as the first film, and after the second step, the second film forming a Schottky junction with the operating layer is deposited. 6. The method for manufacturing a compound semiconductor device according to claim 5, wherein the second film is made of a refractory metal or a compound thereof. 7. The method of manufacturing a compound semiconductor device according to claim 1, wherein a conductive film forming a Schottky junction with the operation layer is formed as the first film. 8. The method of manufacturing a compound semiconductor device according to claim 7, wherein the conductive film is made of a refractory metal or a compound thereof. 9. The method for manufacturing a compound semiconductor device according to claim 1, wherein dry etching is performed using SF ₆ gas.