JP2551315B2 - Method for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a gate electrode of a Schottky gate field effect transistor using a compound semiconductor.

[0002]

2. Description of the Related Art In a Schottky gate field effect transistor (FET) using a compound semiconductor, one method of forming a gate electrode is to form it on an operating layer made of a compound semiconductor provided on a semi-insulating GaAs substrate. There is known a method in which an opening corresponding to a gate electrode pattern is provided in the insulating film and a metal layer to be a gate electrode is formed in the opening. 2A to 2F are cross-sectional views shown in order of main steps for explaining the conventional gate electrode forming method.

As shown in FIG. 2A, the semiconductor substrate 2
The operating layer 21 is formed on the surface of 0 by the epitaxial growth method or the ion implantation method, the first insulating film 22 made of SiO ₂ is formed thereon by the CVD method, and the first insulating film 22 is made of WSi or the like. Is formed by a sputter deposition method or the like, and a first resist film 24 having an opening corresponding to the gate electrode pattern is formed on the reflective film 23 by a normal photolithography process. Here, in the reflection film 23, the reflectance of the electron beam of the exposure apparatus changes due to the variation in the thickness of the first insulating film 22.
The resist film 24 is a film for preventing variation in the opening size of the resist film 24, and its formation is essential.

Next, as shown in FIG. 2B, anisotropic dry etching is performed by a reactive ion etching method (RIE method) or the like using the first resist film 24 as a mask, and the reflective film 23 and the An opening corresponding to the gate electrode pattern is formed in the first insulating film 22 while leaving a part of the first insulating film 22. The reason for using anisotropic dry etching for this opening is to process the gate opening pattern for forming a fine gate with good controllability and reproducibility. However, in dry etching having high anisotropy by the RIE method or the like suitable for fine processing, the ion bombardment is strong and the operating layer 21 is damaged, and carriers near the surface are reduced. Conventionally, the reflective film 23 and the first insulating film 22 are opened while leaving a part of the first insulating film 22.
This is to prevent the operating layer 21 from being damaged.

Next, as shown in FIG. 2C, the first resist film 24 is peeled and removed, and the exposed reflection film 23 is exposed.
And SiO ₂ so as to cover the inside of the opening of the first insulating film 22.
The second insulating film 25 made of is formed by the CVD method or the like. Next, as shown in FIG. 2D, the second insulating film 2
No. 5 is formed on the side wall of the opening by a magnetron type RIE method (MIE method) or the like, which has less ion bombardment than the above highly anisotropic dry etching and is less likely to damage the operating layer 21.
Etch back so as to leave the insulating film 25. This makes it possible to form a fine gate opening while suppressing damage to the operation layer 21. The second side wall of the opening
The remaining insulating film 25 is a step necessary to obtain a gate electrode having a gate length equal to or smaller than the size of the opening formed in the first insulating film 22.

Next, as shown in FIG. 2E, an electrode metal layer 26 to be a gate electrode is formed on the entire surface including the surface of the operation layer 21 exposed by the opening by a sputter deposition method or a vacuum deposition method. Next, a second resist film 27 having a gate electrode pattern is formed by a normal photolithography process.

Next, using the second resist film 27 as a mask, the electrode metal layer 26 is etched by ion milling or RIE. Next, the second resist film 27 is stripped and removed by an organic solvent treatment and an O ₂ plasma treatment, and further, the first insulating film 22 and the second insulating film 25 are removed by wet etching. The semiconductor device shown in (f) is obtained.

[0008]

In the above-mentioned conventional method of forming a gate electrode, the second insulating film is easily dry-dissociated for the purpose of preventing damage to the operating layer during dry etching.
SF ₆ gas that can perform etching with less ion bombardment by F radicals is mainly used. When etching is performed using this gas, WS used as a reflective film
Since the selection ratio between i and SiO ₂ is as large as 5 (WSi has a higher etching rate), if the second insulating film on the WSi film is removed, the etching of WSi ends in a short time. , The height of the second insulating film around the opening is about 0.1
A protrusion of μm is generated. Then, the protrusion remains even after the SiO ₂ inside the opening is completely etched, and when the electrode metal layer is formed on the protrusion, the protrusion causes the protrusion as shown in FIG. As a result, a thin portion 28 is generated on the gate electrode, and there is a problem that the gate electrode is broken or damaged.

When an etching gas other than SF ₆ such as CHF ₃ is used, the selection ratio between WSi and SiO ₂ is close to 1, so that the above-mentioned protrusions do not occur, but CF ₃ ⁺ or the like is used. There was a problem that the operating layer was damaged by the impact of ions, and the carriers near the surface were reduced. Therefore, an object of the present invention is to make it possible to form a gate opening having a good shape without protrusions around the opening without damaging the semiconductor operating layer.
Another object of the present invention is to provide a semiconductor device having excellent characteristics and high reliability.

[0010]

In order to achieve the above object, according to the present invention, a semi-insulating compound semiconductor substrate (1
0) forming an operating layer (11) made of a compound semiconductor on the operating layer, and forming a first insulating film (12) on the operating layer;
Forming a reflective film (13) covering the surface of the first insulating film, and a resist film (14) having a gate region opened
And etching the reflective film (13) and the first insulating film (12) by an anisotropic dry etching method using the resist film as a mask to form an opening for leaving a part of the first insulating film. And a step of removing the resist and the reflective film, and a step of forming a second insulating film (15) covering the surface of the first insulating film and the inner wall of the opening of the first insulating film. And etching back the second insulating film by a dry etching method to leave the second insulating film on the side wall of the opening and remove the first insulating film left on the bottom surface of the opening. Selectively exposing the surface of the operating layer, depositing a metal layer (16) and patterning to leave the metal layer in the opening, and etching away the first and second insulating films. Process and Method of manufacturing a semiconductor device, characterized in that, is provided.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. 1A to 1F are cross-sectional views showing main steps in order of steps in order to explain the method of forming a gate electrode according to the present invention. First, as shown in FIG. 1A, on a semiconductor substrate 10 made of semi-insulating GaAs, a carrier concentration of 2 × 10 4 with Si as an impurity is formed as an operating layer 11 by a molecular beam epitaxy method (MBE method). ¹⁷ cm ^-3
The n-type GaAs layer is grown to a film thickness of 2000Å. A first insulating film 12 made of SiO ₂ is formed thereon by a CVD method to a thickness of 6000 Å, and the first insulating film 12 is further formed.
A reflective film 13 made of WSi is formed on the upper surface by a sputter deposition method to a thickness of 1000Å.

Then, a photoresist is spin-coated to a thickness of 5000Å and dried, and then an opening having a length of 0.45 μm and a width of 100 μm corresponding to the gate electrode pattern is formed by a normal photolithography process.
The first resist film 14 is formed. Next, FIG. 1 (b)
As shown in FIG.
Reflective film 1 by RIE method using F ₆ + CF ₄ mixed gas
3 and the first insulating film 12 by the RIE method using a CHF ₃ + O ₂ mixed gas to form an opening having a shape corresponding to the gate electrode pattern. At this time, the first insulating film 12 is left on the bottom surface of the opening to a thickness of about 1000Å.

Next, as shown in FIG. 1C, the first resist film 14 is stripped and removed by an organic solvent treatment and an O ₂ plasma treatment, and then an MIE method using SF ₆ + CF ₄ mixed gas is carried out. the reflective film 13 is removed by, then, the second insulating film 15 made of SiO ₂ on the entire surface including the opening inner wall C
A film having a thickness of 1000 Å is formed by the VD method. Next, FIG.
(D), the second insulating film 15 is etched back by the MIE method using SF ₆ gas to expose the surface of the operating layer 11 on the bottom surface of the opening and the second insulating film 15 on the side wall of the opening. Leave. The length of the opening after this etch back step is about 0.43 μm, which corresponds to an electrode having a desired gate length.
Met. Then, as shown in FIG. 1D, after the etching back process is completed, the second insulating film 15 is formed around the opening.
No protrusion is seen.

Next, as shown in FIG. 1E, 1000 is formed on the entire surface including the surface of the operating layer 11 exposed by the opening.
Å film thickness WSi, 500Å film thickness TiN, 20
A second resist film for sequentially forming the electrode metal layer 16 of Au having a film thickness of 00Å by a sputter deposition method and a vacuum deposition method, and processing the electrode metal layer 16 into a gate electrode pattern by a normal photolithography process. Form 17.

Then, as shown in FIG. 1F, the electrode metal layer 16 is etched into a desired pattern by an ion milling method using Ar using the second resist film 17 as a mask to form a second pattern. The resist film 17 is treated with an organic solvent and O
₂ Remove by plasma treatment. Furthermore, the formation of the Schottky gate electrode is completed by removing the first insulating film 12 and the second insulating film 15 by wet etching.

In the semiconductor device thus formed, as shown in FIG. 1 (f), since the gate electrode is formed in a good shape without a thin portion, the gate electrode may be broken or damaged. Disappears. Further, in the above manufacturing process, the damage to the operation layer 11 due to the dry etching is slight, so that the carriers near the surface of the operation layer 11 are hardly reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. 1 as in the case of the previous embodiment. Also in this embodiment, steps (a) to (c) of FIG. 1 are the same as those in the previous embodiment. In the etch back step after processing into the state of FIG. 1C, SF ₆ is used in this example, which has a small number of radicals even in a high vacuum state, and therefore has a small ion impact and is less likely to damage the operating layer. The ECR method (electron cyclotron resonance method) was applied. After the end of the etch back process using the ECR method, as shown in FIG.
No protrusion of the second insulating film 15 was found around the opening. The length of the opening after this process is 0.42 μm.
Met.

After that, a semiconductor device was manufactured by depositing an electrode metal layer, patterning the same, and removing the first and second insulating films. Also in this example, the Schottky gate electrode had a good shape as shown in FIG. 1 (f). Further, as in the case of the MIE method, almost no decrease in carriers near the surface of the operating layer 11 due to dry etching damage was observed.

[0019]

As described above, according to the method of manufacturing a semiconductor device of the present invention, the second insulating layer for processing the opening of a film such as WSi used as a reflective film during electron beam exposure into a fine shape. According to the present invention, since the film is removed before the film is formed, SF _{6 which} causes less damage to the operating layer.
Even if the second insulating film is etched using gas, W
A protrusion made of SiO ₂ around the opening, which occurs due to a large difference in etching rate between Si and SiO ₂ , does not occur. Therefore, even when a gate electrode is formed on the opening,
It is possible to form a gate electrode having a good shape with no thin portion, and it is possible to avoid breakage or damage of the gate electrode.

The size of the opening after the second insulating film is etched back is about 0.42 to 0.4 which is a size suitable for forming a gate electrode having a length required for the characteristics of the FET.
It can be 3 μm. Further, since damage to the semiconductor operating layer due to dry etching can be suppressed to a low level, it is possible to prevent the reduction of carriers in the vicinity of the surface of the operating layer due to the damage.

[Brief description of drawings]

FIG. 1 is a sectional view showing main steps for explaining an embodiment of the present invention.

FIG. 2 is a cross-sectional view of main steps of a conventional example.

[Explanation of symbols]

10, 20 Semiconductor substrate (semi-insulating GaAs substrate) 11, 21 Operating layer (n-type GaAs layer) 12, 22 First insulating film (SiO ₂ film) 13, 23 Reflective film (WSi film) 14, 24 1st Resist film 15, 25 Second insulating film (SiO ₂ film) 16, 26 Electrode metal layer (WSi / TiN / Au) 17, 27 Second resist film 28 Thin portion

Claims (3)

(57) [Claims] 1. A step of forming an operating layer made of a compound semiconductor on a semi-insulating compound semiconductor substrate and forming a first insulating film on the operating layer; and covering the surface of the first insulating film .
A step of forming a reflective film for reflecting the irradiation beam from the beam source of the exposure apparatus, and a resist film having a gate region opened and using the resist film as a mask by an anisotropic dry etching method. Etching the reflective film and the first insulating film to form an opening that leaves a part of the first insulating film, removing the resist and the reflective film, and the first insulating film A second insulating film that covers the surface of the first insulating film and the inner wall of the opening of the first insulating film, and the second insulating film is etched back by a dry etching method to form the second insulating film on the sidewall of the opening. Remaining insulating film and removing the first insulating film left on the bottom surface of the opening to selectively expose the surface of the operating layer, and depositing a metal layer to form the metal layer in the opening. Putter to leave on The method of manufacturing a semiconductor device characterized by comprising the steps of packaging, and a step of etching away said first and second insulating films. 2. The etching means used when etching back the second insulating film is more preferable than the etching means used when etching the first insulating film to form the opening. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the ion bombardment against the etching product is small. 3. The etching means employed when etching back the second insulating film is one using a magnetron type reactive ion etching method or an electron cyclotron resonance method. 1. The method for manufacturing a semiconductor device according to 1.