JPH11177080A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device wherein, when used for a process such as a gate recess formation process of a semiconductor device such as HEMT(high electron mobility transistor), sufficient adhesion between a resist and a semiconductor device is assured. SOLUTION: An oxide layer 4 is formed on the surface of a semiconductor substrate 20 by an oxygen plasma process. Then, a resist layer 5 of organics is formed on the semiconductor substrate 20 (over the oxide layer 4), and after the resist layer 5 is selectively irradiated by electron beam, a resist pattern is formed in an organic liquid-developer (an opening 6 is formed on the resist layer 5). After that, with the resist pattern 5 used as a mask, the oxide layer 4 exposed through the opening 6 is removed in an alkaline solution, and a pattern wherein the oxide layer 4 exposed through the opening 6 is removed used as a mask, wet-etching is performed to form a recessed groove on the semiconductor substrate 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a HEMT (High El
The present invention relates to a method for manufacturing a semiconductor device used in a step of forming a gate electrode of an ectron mobility transistor (high electron mobility transistor).

[0002]

2. Description of the Related Art In HEMTs, a higher cut-off frequency is required, and a shorter gate length (a shorter gate length of a gate electrode) is required to reduce a noise figure. Because of this requirement, HEMT fabrication
Electron beam exposure capable of forming a fine pattern is used (a method of fine processing using an electron beam resist is used).

[0003] Here, HEMT (High Electron M
obility Transistor: a high electron mobility transistor is an n-type semiconductor having a small electron affinity (for example, n-AlGaAs).
s) and a high-purity semiconductor with a high electron affinity (for example, undoped GaAs) when joining (heterojunction)
FET operation is performed by using electrons (two-dimensional electron gas) with very high mobility that accumulate at the energy level lower than the Fermi level (at the high-purity semiconductor side) at the discontinuity of the band generated at the bottom of the conductor. Transistor.

FIGS. 4 and 5 are views for explaining a conventional method of manufacturing a HEMT. Referring to FIGS. 4 and 5, in the conventional method for fabricating a HEMT, GaAs serving as a channel layer is used.
s layer 1, AlGaAs layer 2 serving as a secondary electron supply layer, high concentration G serving as a source / drain ohmic contact layer
On the HEMT substrate on which the aAs layer 3 is sequentially formed, a positive electron beam resist 5 is applied and baked.
(FIG. 4 (a)).

Next, in order to open a gate forming portion,
Electron beam exposure BM is performed on a portion corresponding to the gate formation region (FIG. 4B). Thereby, the electron beam resist 5
In the above, only the portion corresponding to the gate formation region is exposed. Next, development, washing and drying are performed to form an opening 6 in a portion of the electron beam resist 5 corresponding to the gate forming region (FIG. 4C).

Next, as shown in FIG. 5D, recess etching is performed on the substrate (high-concentration GaAs layer 3) using the electron beam resist 5 (that is, the resist pattern) in which the opening 6 is formed as a mask. 7 is formed (FIG. 5D).

Next, a metal wiring layer 10 for a gate electrode is deposited on the entire substrate (FIG. 5E). Thereby, the metal wiring layer 10 is on the bottom 8 of the recess groove 7 (on the AlGaAs layer 2 exposed by the recess groove 7 in the example of FIG. 5E).
And on the electron beam resist 5.

Thereafter, the metal wiring layer 10 deposited on the bottom 8 of the recess groove 7 in the metal wiring layer 10 is left.
The electron beam resist 5 and the metal wiring layer 10 thereon are removed by a lift-off method (FIG. 5F). In this way,
A semiconductor device in which the metal wiring layer 10 as a gate electrode is formed can be manufactured.

Here, in the step of applying an electron beam resist 5 shown in FIG.
If contamination (particularly organic contamination) is present in the upper part, there arises a problem that the resist 5 reacts with a contaminant on the substrate and the resist 5 is separated from the substrate. In the process of FIG. 4C in which recess etching is performed using the resist 5 as a mask, if the adhesion between the resist 5 and the substrate is weak, the resist 5 is peeled off from the substrate as the etching proceeds. In addition, there is a problem that etching of a fine pattern becomes impossible. As a method for improving the adhesion between the resist and the substrate, Japanese Patent Application Laid-Open No. Hei 5-74669 discloses a method in which hexamethyldisilazane (HMDS) is applied to a substrate and then the resist is applied.

[0010]

SUMMARY OF THE INVENTION However, HMD
Even when S is applied, the adhesive strength of the resist is not sufficient, and the resist may peel off from the substrate during recess etching. Further, the application of HMDS was not at all effective in removing the resist from the substrate due to contaminants.

The present invention provides a method of manufacturing a semiconductor device capable of ensuring sufficient adhesion between a resist and a semiconductor substrate when used in a gate recess forming step of a semiconductor device such as a HEMT. It is intended to be.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a semiconductor device, comprising: a step of subjecting a semiconductor substrate to surface treatment with oxygen plasma to form an oxide layer on the surface of the semiconductor substrate; Forming a resist layer composed of an organic substance on the formed semiconductor substrate, selectively irradiating the resist layer with an electron beam, and then forming a resist pattern with an organic developer, A step of removing an exposed oxide layer with an alkaline solution as a mask, and a step of forming a recess groove in the semiconductor substrate by performing wet etching using the pattern from which the oxide layer has been removed as a mask. It is characterized by:

According to a second aspect of the present invention, in the method of manufacturing a semiconductor device according to the first aspect, the step of surface-treating the semiconductor substrate with oxygen plasma to form an oxide layer on the surface of the semiconductor substrate includes: 10 ~ 100
It is characterized in that an oxide layer having a thickness of Å is formed.

According to a third aspect of the present invention, in the method of manufacturing a semiconductor device according to the first aspect, the step of removing the exposed oxide layer with an alkaline solution using the resist pattern as a mask comprises: The alkali normality is 0.2 to 0.4 N.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect, wherein wet etching is performed using the pattern from which the oxide layer has been removed as a mask to form a recess groove in the semiconductor substrate. Is characterized in that the wet etching is performed with a citric acid / hydrogen peroxide aqueous solution.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are views for explaining a method for manufacturing a semiconductor device according to the present invention. Referring to FIGS. 1 and 2, in the present invention, first, a semiconductor substrate 20 (in the example of FIGS.
AlGaAs layer 2 serving as a secondary electron supply layer 2, high-concentration GaAs layer 3 serving as a source / drain ohmic contact layer
The HEMT substrate 20) on which is sequentially formed are surface-treated with oxygen plasma 21 (FIG. 1A). That is, the oxide layer 4 is formed on the surface of the semiconductor substrate 20 by the oxygen plasma treatment. Next, a resist layer 5 composed of an organic substance is formed on the semiconductor substrate 20 (on the oxide layer 4) (FIG. 1B), and the resist layer 5 is selectively irradiated with an electron beam. A resist pattern is formed with the liquid (an opening 6 is formed in the resist layer 5) (FIG. 1C). Thereafter, using the resist pattern 5 as a mask, the oxide layer 4 exposed through the opening 6 is removed with an alkaline solution (FIG. 2D). Then
Using the pattern from which the oxide layer 4 exposed through the opening 6 has been removed as a mask, wet etching is performed to form a recess groove 7 in the semiconductor substrate 20 (FIG. 2E).

In the process example shown in FIG. 1, the surface treatment is performed on the substrate 20 by the oxygen plasma 21 before the application of the resist layer 5 composed of an organic substance (the oxide layer 4 is formed on the surface of the substrate 20). Therefore, contaminants on the substrate surface can be removed, and the adhesion between the resist layer 5 and the substrate 20 can be improved. As a result, side etching when performing wet etching in the step of FIG. 2E is prevented, and a recess groove 7 having a good shape and uniform dimensions can be obtained.

Further, since treatment with an alkali solution is performed after development with an organic developer, the oxide layer 4 formed by the oxygen plasma treatment can be surely removed. As a result, wet etching can be performed in the step of FIG. When performed, a uniform etched surface can be obtained.

It should be noted that the semiconductor substrate 20 is
In the step of FIG.
It is preferable to form an oxide layer 4 having a thickness of 10 to 100 degrees on zero. Thereby, a stable layer is formed on the surface of the substrate 20, and the adhesion to the resist layer 5 can be further improved.

In the step of FIG. 2D in which the oxide layer 4 exposed through the opening 6 is removed with an alkaline solution using the resist pattern 5 as a mask, the alkali normality of the alkaline solution is set to 0.2 to 0. 4N is recommended. Thereby, the surface of the semiconductor substrate 20 can be mirror-finished, and the oxide layer 4 can also be removed.

The oxide layer 4 exposed by the opening 6
In the step shown in FIG. 2E in which the recessed groove 7 is formed in the semiconductor substrate 20 by performing wet etching using the pattern from which is removed as a mask, the wet etching is preferably performed with an aqueous citric acid / hydrogen peroxide solution. Thereby, H
When the recess groove 7 is formed in the EMT substrate 20 (1, 2, 3), only the high concentration GaAs layer 3 can be selectively etched.

[0022]

Next, an embodiment of the present invention will be described.
In this embodiment, first, as shown in FIG. 1A, a GaAs layer serving as a channel layer and an AlG layer serving as a secondary electron supply layer are formed.
An HEM in which an aAs layer 2 and a high-concentration GaAs layer 3 serving as source / drain ohmic contact layers are sequentially formed.
A T substrate 20 was prepared, and the surface of the HEMT substrate 20 was subjected to a plasma treatment with oxygen plasma 21. The conditions of the plasma treatment are as follows: O ₂ flow rate 200 sccm, pressure 1 Torr, RF
The test was performed at a power of 200 W for 20 minutes. By this step, organic substances on the substrate surface are completely removed, and Ga, As,
An oxide layer 4 made of O was formed.

FIG. 3 is a diagram showing a change in ellipsometric angle before and after plasma processing. In FIG. 3, λ
Is the wavelength of the incident light, and φ is the incident angle of the light. Referring to FIG. 3, since the ellipsometric angle changes before and after the plasma processing, it can be said that some thin film is formed on the substrate 20.

Next, as shown in FIG. 1B, a resist 5, which is formed of an organic substance, for example, ZEP520 (manufactured by Zeon Corporation) is applied to a thickness of about 2000.degree. Baking was performed in a nitrogen atmosphere. Thereafter, a line pattern was drawn on the resist 5 using an electron beam drawing apparatus. The drawing conditions were as follows: acceleration voltage 20 kV, irradiation current value 0.1 nA, beam diameter 0.025 μm, line irradiation amount 20
Drawing was performed under the condition of 0 nC / cm.

Thereafter, as shown in FIG. 1C, the resist 5 is developed at room temperature for 3 minutes using an organic developer ZED50N (manufactured by Zeon Corporation), and then rinsed with isopropyl alcohol for 1 minute at room temperature. Then, an opening (resist opening) 6 was formed in the resist 5.

Next, development was carried out at room temperature for 45 seconds using an alkali developing solution NMDW (manufactured by Tokyo Ohka) having an alkali normality of 0.27 N, followed by rinsing with pure water at room temperature for 1 minute. By development with this alkali developer,
As shown in FIG. 2D, the GaAs oxide 4 on the substrate surface exposed by the resist opening 6 was removed.

Thereafter, as shown in FIG. 2E, etching was performed with a citric acid / hydrogen peroxide-based etchant using the resist pattern 5 as a mask to form a recess groove 7 in the substrate 20. That is, the high-concentration Ga
The As layer 3 is etched and AlGaAs is formed on the substrate surface.
Layer 2 was exposed.

In this example, a HEMT was manufactured as a semiconductor device as described above. At this time, sufficient adhesion between the resist 5 and the substrate 20 can be ensured, and it is possible to avoid a situation in which the resist 5 peels off from the substrate as the etching progresses, and perform good recess etching. Yes (good recess grooves could be obtained).

[0029]

As described above, according to the first aspect of the present invention, the step of forming the oxide layer on the surface of the semiconductor substrate by treating the surface of the semiconductor substrate with oxygen plasma and the step of forming the oxide layer are performed. A step of forming a resist layer composed of an organic substance on a semiconductor substrate, and after selectively irradiating the resist layer with an electron beam, a step of forming a resist pattern with an organic developer and using the resist pattern as a mask Having a step of removing the exposed oxide layer with an alkaline solution, and performing a wet etching using the pattern from which the oxide layer has been removed as a mask to form a recess groove in the semiconductor substrate, Surface treatment of the substrate with oxygen plasma before applying the resist layer composed of organic substances can remove contaminants on the substrate surface and improve the adhesion between the resist film and the substrate And it can be, so that side etching when subjected to wet etching is prevented as it is possible to obtain a recess (groove) having a good shape and uniform size. In addition, since treatment with an alkali solution is performed after development with an organic developer, an oxide layer formed by oxygen plasma treatment can be removed. As a result, a uniform etching surface can be obtained when wet etching is performed.

According to a second aspect of the present invention, in the method of manufacturing a semiconductor device according to the first aspect, the step of surface-treating the semiconductor substrate with oxygen plasma to form an oxide layer on the surface of the semiconductor substrate includes: 10Å ~ on the substrate
Since the oxide layer having a thickness of 100 ° is formed, a stable layer is formed on the substrate surface, and the adhesiveness with the resist can be further improved.

According to a third aspect of the present invention, in the method of manufacturing a semiconductor device according to the first aspect, the step of removing the exposed oxide layer with an alkaline solution using the resist pattern as a mask is performed. Since the alkali normality of the solution is 0.2 to 0.4 N, the surface of the semiconductor substrate can be mirror-finished and the oxide layer can be removed.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor device according to the first aspect, wet etching is performed using the pattern from which the oxide layer has been removed as a mask to form a recess in the semiconductor substrate. In the process,
Since the wet etching is performed with a citric acid / hydrogen peroxide aqueous solution, only the high-concentration GaAs layer can be selectively etched when forming the recess in the HEMT.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a method for manufacturing a semiconductor device according to the present invention.

FIG. 2 is a diagram illustrating an example of a method for manufacturing a semiconductor device according to the present invention.

FIG. 3 is a diagram showing a change in ellipsometric angle before and after plasma processing.

FIG. 4 is a diagram showing a conventional method for manufacturing a semiconductor device.

FIG. 5 is a diagram illustrating a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 GaAs layer 2 AlGaAs layer 3 high concentration GaAs layer 5 resist 6 opening 7 recess groove 8 bottom of recess groove 20 semiconductor substrate 21 oxygen plasma

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 21/316

Claims (4)

[Claims] A step of forming an oxide layer on the surface of the semiconductor substrate by surface-treating the semiconductor substrate with oxygen plasma; and a step of forming a resist layer made of an organic material on the semiconductor substrate on which the oxide layer has been formed. Forming a resist pattern with an organic developer after selectively irradiating the resist layer with an electron beam; removing the exposed oxide layer with an alkaline solution using the resist pattern as a mask; Forming a recess in the semiconductor substrate by performing wet etching using the pattern from which the layer has been removed as a mask. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the step of surface-treating the semiconductor substrate with oxygen plasma to form an oxide layer on the surface of the semiconductor substrate includes forming a film of 10 to 100 ° on the semiconductor substrate. A method for manufacturing a semiconductor device, comprising forming a thick oxide layer. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the step of removing the exposed oxide layer with an alkali solution using the resist pattern as a mask has an alkali normality of the alkali solution of 0.2 to 0.2. A method for manufacturing a semiconductor device, comprising: 0.4N. 4. The method for manufacturing a semiconductor device according to claim 1, wherein wet etching is performed using the pattern from which the oxide layer has been removed as a mask, and the wet etching is performed using citric acid /
A method for manufacturing a semiconductor device, wherein the method is performed with an aqueous solution of hydrogen peroxide.