JPH03185826A - Manufacture of semiconductor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing a semiconductor device in which fine electrodes such as gate electrodes are formed on the surface of a semiconductor substrate by a lift-off method.

[Prior art] In order to form fine metal electrodes (with a width of 1 μm or less) such as gate electrodes of high-frequency field effect transistors using the lift-off method, an inversely tapered opening is formed in the mask with good reproducibility. It is necessary to form.

Conventionally, a lift-off method is known in which an insulating film called a spacer is used together with a resist film as a mask.

This conventional technique will be explained using FIGS. 2(a) to 2(cl).

An insulating film 2 is deposited on a semiconductor substrate 1, and a resist film 3 with an opening 4 is formed thereon by photolithography. (FIG. 2(a)) Anisotropic dry etching is performed using the resist M3 as a mask to remove the insulating film 2 in the opening 4 and expose the semiconductor substrate 1. (Figure 2(b)
)) In order to facilitate lift-off and control the characteristics of the field effect transistor, the side surface of the insulating film 2 of the opening 4 is recessed by a certain amount from the side surface of the resist film 3 by wet etching, and the opening on the side of the semiconductor substrate l is recessed by wet etching. The width is wider than that of the resist film 3 (inverted tapered shape). (Figure 2 (
C)) Finally, a desired electrode 5 can be formed by depositing a metal film and removing (lift-off) the metal film other than the opening 4 by dissolving and removing the resist 3. (Figure 2(d)
) [Problems to be Solved by the Invention] However, in the above-mentioned anisotropic dry etching, it is known that organic high molecular substances called polymers may be deposited non-uniformly on the side surfaces of the openings and the semiconductor surface depending on the etching conditions. It is being In particular, when a silicon oxide film (S i O,) is used as an insulating film, CF4+H, CHF, gas, which has a high etching selectivity for resist films and semiconductor substrates, is used, so the deposition of such polymers is difficult. It becomes more noticeable.

Therefore, there is a problem in that the polymer deposited on the exposed semiconductor substrate inhibits contact between the electrode and the semiconductor substrate.

In order to solve this problem, it is known to (1) reduce polymer deposition by controlling etching conditions, and (2) remove polymer by oxygen ashing or the like.

However, (1) etching conditions for reducing polymer deposition and etching conditions that provide a high selectivity for the resist film and semiconductor substrate do not usually match. As a result, it is difficult to reduce polymer deposition when forming fine electrodes in order to obtain better characteristics of semiconductor devices or when increasing the dimensional accuracy of openings as the degree of integration increases.

In addition, ■When removing polymer by oxygen ashing, etc., oxygen ashing not only oxidizes the polymer, but also removes the resist film and changes its dimensions greatly, so it is important to form fine electrodes with high dimensional accuracy. is impossible.

The present invention solves the above problems, and its purpose is to:
The object of the present invention is to provide a method for manufacturing fine electrodes that have excellent contact with the semiconductor surface and excellent dimensional accuracy.

[Means and effects for solving the problem] The present inventors
From Inana's experiments, it was discovered that the above-mentioned polymer does not occur when the surface of the semiconductor is covered with an insulating film, but occurs when the surface of the semiconductor is exposed. This led to the idea that by stopping anisotropic dry etching before the semiconductor surface is exposed and removing the remaining insulating film by wet etching, it is possible to create openings without polymer deposition.

A method of manufacturing a semiconductor device according to the present invention includes a first step of forming an insulating film on a semiconductor substrate, forming a resist film with openings in a predetermined region on the insulating film, and forming an insulating film in the predetermined region on the semiconductor substrate. a second step of performing anisotropic dry etching to leave a predetermined film thickness that is not exposed; a third step of removing the remaining insulating film in the predetermined region by wet etching; and a third step of removing the remaining insulating film in the predetermined region by wet etching; This step consists of a fourth step of forming electrodes on the semiconductor substrate.

The insulating film is, for example, a silicon oxide film or a silicon nitride film, and is generally formed by a plasma CVD method or a sputtering method.

The anisotropic dry etching technique is a technique for selectively etching in a direction perpendicular to the principal surface of a semiconductor substrate, and includes reactive sputter etching, reactive ion etching, and the like. As the gas for etching the insulating film, a gas with a high selectivity such as CF4+H, CHF, CHF, or Senju activated gas is used.

When etching an insulating film made of oxide with these gases, the polymer generated during etching is deposited on the resist film, and at the same time, the active oxygen atoms generated while the insulating film made of oxide is being etched , polymers made of organic matter are decomposed and not deposited. In addition, even if the polymer is not decomposed by active oxygen atoms, the dry etching is still in progress, so the polymer deposited on the surface of the insulating film will be lifted off when the remaining insulating film is removed in the next wet etching process. is removed and does not remain on the semiconductor substrate.

The wet etching is a technique for chemically dissolving and removing the insulating film using an etching solution such as HF-NH or F aqueous solution.

【Example〕

As an embodiment of the present invention, a method for forming a Schottky gate electrode of a GaAs field effect transistor is shown in FIG. 1(a).
This will be explained below using (d).

In the first step shown in FIG. 1(a), an insulating film 2 made of silicon oxide and deposited by RF sputtering to a thickness of 0.5 μm is formed on a semiconductor substrate l made of GaAs. Then, a resist film 3 (
The film thickness is 0.5 μm).

In the second step shown in FIG. 1(b), the insulating film 2 in the opening 4 is anisotropically dry etched leaving a film thickness of about 50 nm. For anisotropic dry etching, a parallel plate type reactive ion etching device is used, and the etching gas is CHF.
, +Ar (flow rate ratio Ar/CHF, is O ~ 10, pressure is 6
~12Pa), and the high frequency power is 350~600W
It is. In this step, the insulating film 2' left in the opening 4 is
No polymer is deposited on top.

The thickness of the remaining insulating film 2' is numerically about 10% (5% or more and 15% or less) of the film thickness of the insulating film 2. In order not to expose the surface of the semiconductor substrate 1 at all, it is necessary to leave a film thickness that is greater than the in-plane variation due to anisotropic dry etching. On the other hand, if this film thickness is large, there will be large variations in wet etching in the next step, and the shape accuracy of the opening 4 will deteriorate.

In the third step shown in FIG. 1(C), HF-NH,
The insulating film 2' left in the opening 4 is completely etched using an F aqueous solution. As a result, the semiconductor substrate 1 is exposed, and the insulating film 2 on the side surface of the opening 4 retreats from the resist film 3, forming an inverted tapered opening 4 that facilitates lift-off.
' is formed.

In the fourth step shown in FIG. 1(d), the semiconductor substrate 1
Ti/Pt/A forming a Schottky junction with
After forming the metal layer u (about 20 nm thick), the resist film 3 is dissolved and removed to form the electrode 5. As a result, there is nothing on the surface of the semiconductor substrate 1, such as a polymer, that inhibits contact with the electrode 5, and good contact can be obtained.

Although GaAs was used as the semiconductor substrate 1, Si
However, it is possible to implement the same method. In addition, the insulating film 2
Although an example in which a silicon oxide film is used as the material is shown, a silicon oxide film doped with phosphorus or the like or a silicon nitride film may also be used.

In this example, CHF and +Ar are used as the gases used for anisotropic dry etching, but Ar
Other inert gases such as He may be used instead of CF4.
The same operation can be performed using only +H or CHF.

〔Effect of the invention〕

As described above, the method for manufacturing a semiconductor device according to the present invention includes the first step of forming an insulating film on a semiconductor substrate, forming a resist film with openings in a predetermined region on the insulating film, and a second step of anisotropic dry etching the insulating film leaving a predetermined film thickness that does not expose the semiconductor substrate; a third step of removing the remaining insulating film in the predetermined region by wet etching; and a fourth step of forming electrodes on the semiconductor substrate exposed by wet etching.

Therefore, according to the present invention, no polymer is deposited on the semiconductor surface or the insulating film, and an opening with excellent dimensional accuracy is formed. This makes it possible to obtain good contact with the semiconductor substrate and to form an electrode with desired dimensions.

Further, according to the present invention, since no special process is required to remove the polymer, the process can be simplified, and the only processes that affect the size of the opening are the photolithography process and the dry etching process. ,
The dimensional controllability of the opening can be improved.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are cross-sectional views for explaining one embodiment of the present invention, and FIGS. 2(a) to (cl) are cross-sectional views for explaining the steps of the conventional technology. . In the figure, 1... semiconductor substrate, 2.2''... insulating film, 3...
Resist film, 4.4'...opening, 5...electrode. Figure 1

Claims (2)

[Claims] (1) A first step of forming an insulating film on a semiconductor substrate and forming a resist film with openings in a predetermined region on the insulating film, and forming the insulating film in the predetermined region to a predetermined film thickness such that the semiconductor substrate is not exposed. a second step of performing anisotropic dry etching leaving the remaining insulating film in the predetermined region, a third step of removing the remaining insulating film in the predetermined region by wet etching, and forming an electrode on the semiconductor substrate exposed by the wet etching. A method for manufacturing a semiconductor device, comprising a fourth step of: (2) In the anisotropic dry etching, CF_4+H_2, CHF_3 and CH
2. The method of manufacturing a semiconductor device according to claim 1, wherein any one of F_2+inert gas is used.