JP2765566B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device using a compound semiconductor, and more particularly to a method for manufacturing a compound semiconductor field effect transistor having a recess structure.

[0002]

2. Description of the Related Art MESFETs using GaAs (metal-
Semiconductor field effect transistor) and Al _x Ga _1-x As
In an HJFET (heterojunction field effect transistor) using (0 <x <1) or the like, a highly doped low-resistance layer (contact layer such as GaAs) such as GaAs is formed on the channel layer in order to reduce the resistance between the gate and the source. ) Is provided, and a gate is formed by etching and removing a contact layer of a gate portion to a channel layer using a photoresist as a mask.

[0003] This prior art will be described with an example.

For example, as described in JP-A-7-86309, a high-purity GaAs buffer layer 2 and an n-type Al _x Ga
_1-x As electron supply layer 3 and n-type GaAs contact layer 4
Are sequentially deposited to prepare a compound semiconductor substrate. Next, ohmic electrodes for source and drain (source electrodes 6,
The gate electrode 7) is formed by a lift-off method.

[0005] Next, wet etching or dry etching of Al _x Ga _{1 -x} As and GaAs at a constant speed,
Alternatively, a recess structure is formed by selective wet etching or dry etching in which the rate of removing Al _x Ga _{1 -x} As is extremely small as compared with GaAs, and a metal gate is formed by a vapor deposition / lift-off method. The resist film used for the lift-off is removed using a stripper, and oxygen plasma treatment is performed. At this time, a natural oxide film or an oxide film formed on the surface of the Al _x Ga _{1 -x} As layer 3 by oxygen plasma is removed by hydrochloric acid treatment, and then a surface protective film for stabilizing the surface of the recess opening is formed. Then, the electrode portion is opened to complete.

[0006] As a gate metal material, low resistance Al _x
Al (aluminum) having a stable interface with the Ga _1-x As electron supply layer 3 is used, or a portion in direct contact with the Al _x Ga _1-x As is formed at a high level where the electron gun vapor deposition such as the Mo film 9-1 can be performed. A melting point metal, and an Au film 9-
4 is widely used. In this case, to improve the adhesion between the Au film and the refractory metal,
In general, a two-layer structure of a Ti film 9-2 and a Pt film 9-3 is sandwiched between the two metals.

[0007]

In a field effect transistor having a recess structure, a surface protective film is generally deposited on a recess opening in order to stabilize device characteristics.

It is known that a surface protective film greatly affects device characteristics. In particular, a clean interface between the protective film and the semiconductor surface of the recess opening results in good device characteristics with little leakage current. . Actually, an oxide film is unintentionally formed in the Al _x Ga ₁ -xAs layer on the surface of the recess opening before the protective film is grown, and it is necessary to remove the oxide film.

The conventional problem is that when a hydrochloric acid treatment is performed as a pretreatment for forming the surface protective film, Al or T
i is eroded, causing damage to the gate.
The reason is that Al and Ti are easily oxidized by hydrochloric acid.

When the gate electrode is formed of an Al single layer film, the hydrochloric acid treatment causes a shape change or peels off from the Al _x Ga _{1 -x} As layer. Also, a Ti film 9 for improving the adhesion between the refractory metal film and the Al film.
When -2 is eroded as shown in FIG. 5, the high melting point metal film (9-1) and the Au film 9-4 are easily separated, which is likely to cause mechanical damage to the gate electrode.

It is an object of the present invention to provide a method of manufacturing a semiconductor device including a field effect transistor forming step capable of removing an oxide film before forming a protective film without adversely affecting a gate electrode.

[0012]

According to a first method of manufacturing a semiconductor device of the present invention, when forming a Schottky gate electrode in contact with a compound semiconductor layer containing arsenic by a lift-off method, the method for the lift-off method is used. After the resist film is removed, an oxide film on the surface of the compound semiconductor layer is removed by a water washing treatment, and then a field effect transistor forming step of applying a surface protective film is included.

According to a second method of manufacturing a semiconductor device of the present invention, a resist film pattern is formed on a surface of a compound semiconductor substrate.
The compound semiconductor substrate is etched using the resist film pattern as a mask to form a recessed portion, exposing a compound semiconductor layer containing arsenic on the bottom surface, depositing a conductive film, and forming the resist film pattern and the conductive film on the resist film pattern. Removing the oxide film on the surface of the compound semiconductor layer selectively covered with the Schottky gate electrode by performing a water washing process,
And a step of applying a surface protective film.

The compound semiconductor layer containing arsenic is Al _y Ga
_It may be a _1-y As layer (0 ≦ y ≦ 1).

The washing process can be performed with deionized water or electrolytic ionized water.

The oxide film on the surface of the compound semiconductor layer containing arsenic selectively covered with the Schottky electrode is removed by water. Since this oxide film is considered to be a mixture containing water-soluble As ₂ O _{3 and the} like, oxides that are almost insoluble in water are also removed.

[0017]

Next, a first embodiment of the present invention will be described.

First, as shown in FIG. 1A, an undoped high-purity GaAs buffer layer 2 having a thickness of 600 nm is formed on a semi-insulating GaAs substrate 1, and a Si-doped layer (Nd = 2 × 10 ¹⁸ cm) is formed with a thickness of 40 nm. ^-3 ) n-type Al _x Ga _{1 -x} As
The electron supply layer 3 is 80 nm thick and is Si-doped (Nd = 3.
An n-type GaAs contact layer 4 of 5 × 10 ¹⁸ cm ⁻³ ) is epitaxially grown in sequence using a well-known molecular beam epitaxy (MBE) method. The Al composition ratio x of the n-type Al _x Ga _{1 -x} As electron supply layer 3 was set to 0.25.

Next, a source electrode 6 and a drain electrode 7 made of a vapor-deposited AlGeNi film are formed by using a well-known photolithography method and a lift-off method. Source electrode 6
And the drain electrode 7 are formed after forming the AlGeNi deposited film.
The AuGeNi vapor-deposited film and the n-type GaAs contact layer 4 were alloyed in an H ₂ atmosphere at about 400 ° C. to form a low-resistance ohmic junction.

Next, as shown in FIG. 1B, an opening of 0.2 μm is provided in the electron beam resist film by using an electron beam exposure apparatus so that the gate electrode length Lg is 0.2 μm. A pattern 8 is formed, and GaAs and Al _x Ga
Using a plasma of a mixed gas of BCl ₃ and SF ₆ having a high _1-x As selectivity, ion etching of the n-type GaAs layer 4 in this opening is performed. At this time, by setting the etching rate of GaAs to about 100 times or more the etching rate of Al _x Ga _{1 -x} As, the n-type Al _x G
The recess portion 10 can be formed without substantially etching the a _1-x As electron supply layer 3.

Next, as shown in FIG. 1C, by removing the resist film pattern 8 after depositing the gate metal, the gate metal on the electron beam resist film is lifted off, and as shown in FIG. A gate electrode 9 is formed as shown in FIG. As the gate metal, an Al film 11 was deposited to a thickness of 300 nm.
When the electron beam resist film is removed, it is immersed in a stripping solution and then subjected to oxygen plasma treatment. By this oxygen plasma treatment, an oxide film (3) is formed on the surface of the Al _x Ga _{1 -x} As film (3) in the recess. (Not shown) are formed unintentionally.

Thereafter, the Al _{x in the} recessed portion is washed with water.
After removing the oxide film on the surface of the Ga _1-x As film, as shown in FIG. 2, an SiO ₂ film 12 is deposited as a surface protective film to a thickness of 100 nm by a CVD method to complete the field effect transistor. What was used for the water-washing process was one having an electrical resistivity of 17 MΩ · cm (25 ° C.) (deionized water) manufactured using a normal ion exchange resin.

Since the surface oxide film is considered to be a mixture containing As ₂ O ₃ which is soluble in water, Al _{2 which is} hardly soluble in water is used.
It is considered that O ₃ and Ga ₂ O ₃ are also removed at the same time.
The Alx Ga1-x As film surface oxide film in the recess is removed by washing with water without using acid. Al of the gate metal is not eroded, and a rectifying Schottky gate electrode with low leakage current is reproduced. And the yield of the field effect transistor is 10% as compared with the conventional manufacturing method.
This has improved.

Next, a second embodiment of the present invention will be described.

First, as shown in FIG. 3A, as in the first embodiment, a layer having a thickness of 5 mm is formed on a semi-insulating GaAs substrate 1A.
00 nm undoped high-purity GaAs buffer layer 2
A, 30 nm thick and Si-doped (Nd = 2 × 10 ¹⁸ cm)
^-3 ) n-type AlxGa1 _- xAs electron supply layer 3A, thickness 7
An n-type GaAs contact layer 4A having a thickness of 0 nm and doped with Si (Nd = 3.5 × 10 ¹⁸ cm ⁻³ ) is epitaxially grown in sequence using a well-known molecular beam epitaxy (MBE) method. The Al composition ratio x of the n-type Al _x Ga _{1 -x} As electron supply layer 3A was set to 0.20.

Next, a source electrode 6A and a drain electrode 7A made of a deposited AuGeNi film are formed by using a well-known photolithography method and a lift-off method. The source electrode 6A and the drain electrode 7A after AuGeNi deposited film formation, AuGeNi and n in H ₂ atmosphere of approximately 400 ° C.
The type GaAs contact layer 4A was alloyed to form a low-resistance ohmic junction.

Next, as shown in FIG. 3B, an opening of 0.2 μm is formed in the electron beam resist film by using an electron beam exposure apparatus so that the gate electrode length Lg is set to 0.2 μm. To form GaAs and Al _x Ga _1-x
By using a citric acid-based etchant having a large As selectivity (citric acid 50%: H ₂ O ₂ 30% = 3: 1), the etching rate of the n-type GaAs in the opening is set to be about 100 times or more. , N-type Al _x Ga _{1 -x} As electron supply layer 3A
OA can be formed.

Next, as shown in FIG. 4A, after depositing the gate metal, the resist film pattern 8A is removed, thereby forming the gate on the resist film pattern 8A as shown in FIG. 4B. The metal is lifted off and the gate electrode 9
A is formed. The gate metal is a 50 nm Mo film 9-1.
A, 5 nm Ti film 9-2A, 5 nm Pt film 9-3
A, a 400 nm Au film 9-4A was deposited in this order.
The resist film pattern 8A is removed using a stripping solution, and oxygen plasma processing is performed. By this oxygen plasma processing, an oxide film (not shown) is formed unintentionally on the surface of the recess Al _x Ga _1-y As film 4A. .

Thereafter, the recess portion Al _x G is formed by washing with water.
After removing the surface oxide film of the a _1-x As film 4A, FIG.
As shown in (c), a Si ₃ N ₄ film is deposited as a surface protection film 12 by a CVD method to a thickness of 100 nm to complete the field effect transistor. What was used for the water washing process was electrolytic ionized water (electrolytic anode water) having a pH of 1.7.

In this embodiment, the recess portion Al _x Ga
_{Since the 1-x} As film surface oxide film is washed with water without using an acid, the gate metal Ti film 9-2A is not eroded. The yield of the effect transistor was improved by 10% or more as compared with the conventional case, and a field effect transistor having a Schottky gate electrode having a high yield, a small leakage current and a good rectifying property was obtained.

As described above, the etching for forming the recess may be performed by either reactive ion etching or wet etching, and the washing process may be performed by using either deionized water or electrolytic ionic water. Good results are obtained.

The HJFET having the Al _x Ga _1-x layer as the electron supply layer has been described above as an example. However, in the method of manufacturing the FET in which the gate electrode is formed in the recess by the lift-off method, the HJFET is exposed at the bottom of the recess. As the material of the compound semiconductor layer, GaAs, AlAs, In _z Ga _{1 -z} As
The present invention can be applied as long as it has As as a constituent element, such as.

[0033]

As described above, according to the present invention, after a Schottky gate electrode is formed in a recess portion using a lift-off method, an oxide film on the bottom surface of the recess selectively covered with the Schottky gate electrode is washed with water. As a result, the Schottky gate electrode is not adversely affected by erosion or the like, so that a semiconductor device having a field effect transistor with good characteristics and low leakage current can be manufactured at a high yield.

[0034]

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views illustrating a first embodiment of the present invention in the order of steps, which are separately illustrated in FIGS.

FIG. 2 is a cross-sectional view shown after FIG. 1;

FIGS. 3A and 3B are cross-sectional views in the order of steps, for explaining the second embodiment of the present invention.

FIG. 4 is a cross-sectional view in the order of steps, which is shown separately in FIGS.

FIG. 5 is a cross-sectional view for explaining a conventional example.

[Explanation of symbols]

Reference Signs List 1,1A semi-insulating GaAs substrate 2,2A high-purity GaAs buffer layer 3,3An n-type Al _x Ga _1-x As electron supply layer 4,4An-type GaAs contact layer 5 Two-dimensional electron gas 6,6A Drain electrode 7 , 7A Source electrode 8, 8A Resist film pattern 9, 9A Gate electrode 9-1, 9-1A Mo film 9-2, 9-2A Ti film 9-3, 9-3A Pt film 9-4, 9-4A Au film

Claims (5)

(57) [Claims] When forming a Schottky gate electrode in contact with a compound semiconductor layer containing arsenic by a lift-off method, an oxide film on the surface of the compound semiconductor layer is washed with water after removing the resist film for the lift-off method. Remove with
A method for manufacturing a semiconductor device, comprising a step of forming a field-effect transistor for applying a surface protective film. 2. A resist film pattern is formed on the surface of the compound semiconductor substrate, and the compound semiconductor substrate is etched using the resist film pattern as a mask to form a recessed portion, exposing a compound semiconductor layer containing arsenic on the bottom surface. Forming a Schottky gate electrode by depositing a conductive film and removing the resist film pattern and the conductive film on the resist film pattern; and performing a water washing process to selectively cover the compound semiconductor with the Schottky gate electrode. A method for manufacturing a semiconductor device, comprising: a step of removing an oxide film on a layer surface; and a step of applying a surface protective film. 3. The method according to claim 1, wherein the compound semiconductor layer containing arsenic is Al _y Ga
3. The method for manufacturing a semiconductor device according to claim 1, wherein the _1-y As layer (0 ≦ y ≦ 1). 4. The method of manufacturing a semiconductor device according to claim 1, wherein a washing process is performed with deionized water. 5. The method for manufacturing a semiconductor device according to claim 1, wherein a water washing process is performed with electrolytic ionic water.