JPH03230579A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make the grounding of surface-side electrode possible by side- etching the first substrate-side mask pattern while making an anisotropic etching process to a semiconductor substrate so as to form a widened through hole. CONSTITUTION:The position of a substrate exposed by the openings of the first and second mask patterns 11 and 12 corresponds to the position of a source electrode 3 on a semiconductor layer 2. When anisotropic etching is performed on the semiconductor substrate composed of the substrate 1 and layer 2 by using a mixed gas of CCl2F2 and Ar as an etchant, the substrate 1 is removed in the depth direction. During the process where the substrate 1 is removed, the first mask pattern 11 is also side etched and, as a result, a through hole is formed. When the through hole is formed and the rear surface of the electrode 3 is exposed, the side wall of the through hole becomes to have a fixed inclination. As a result, the double mask of an insulating film 11 and metallic film 12 is removed and a rear conductor film 7 has a fixed thickness even on the side wall of the through hole. Therefore, the source electrode 3 can be grounded well, with a parasitic circuit element being sufficiently reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing an extraction electrode.

[Conventional technology]

FIG. 2 shows a cross-sectional view of a semiconductor device conventionally used in a high frequency band. After performing ion implantation, etc. on the front side of a semiconductor substrate in which a semiconductor layer 2 is provided on a semi-insulating substrate 1, a source electrode 3, a gate electrode 4, and a drain electrode 5 are formed, and a field effect transistor (FET) is formed. Create.

Thereafter, a through hole 6 is formed in the semiconductor substrate, and a back conductive film 7 made of metal is formed on the entire back surface. This via-hole technology allows grounding with a minimum of parasitic circuit elements, and is therefore widely used in high-frequency semiconductor devices.

[Problem to be solved by the invention]

Methods for forming via holes include a method using wet etching and a method using dry etching. In the former method, as shown in FIG. 3(a), a mask 8 is formed on the back surface of the substrate 1, and the semiconductor substrate is etched through the opening thereof. However, according to this method, side etching is significantly involved, resulting in an opening larger than the desired size, and the via hole protrudes beyond the size of the electrode 3 on the front side, resulting in a hole or the electrode 3 sinking. Defects occur and the yield decreases. In addition, the uniformity is poor, and there are some areas where via holes are open and others where they are not.The latter method uses a metal mask of Nl, AI, etc.
ve Ion Etching) and ECR (Elec
tron Cyclotron Re5onance)
The substrate is etched using a method such as etching.

At this time, if appropriate etching conditions are selected, a nearly vertical etching profile can be obtained (anisotropic etching).
. However, after removing the metal mask, in order to ground the electrode 3 on the front side, metal such as TI/Au is deposited from the back side to form a back conductive film 7, as shown in FIG. 3(b). However, there was a problem in that the metal adhesion on the sidewalls of the via holes was insufficient, making it impossible to sufficiently reduce parasitic circuit elements.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a semiconductor device that can solve the problems of the above-mentioned prior art.

[Means to solve the problem]

A method for manufacturing a semiconductor device according to the present invention includes selectively etching a semiconductor substrate having an electrode formed on the front surface from the back side to form a through hole reaching the back side of the electrode, and covering the semiconductor substrate with a conductive material from the back side. A method for manufacturing a semiconductor device in which a conductive film is formed on the back surface of the semiconductor substrate, the wall surface of the through hole, and the back surface of the electrode by sequentially covering the back surface of the semiconductor substrate with a first mask material and a second mask material. a first step of forming first and second mask patterns having openings at positions corresponding to the electrodes; and a step of forming first and second mask patterns having openings at positions corresponding to the electrodes; 2
a second step of anisotropically etching the semiconductor substrate through the openings in the mask pattern to form a through hole; and a third step of removing the conductive material by removing the first and second mask patterns. It is characterized by having the following.

[Effect]

According to the present invention, the first mask pattern on the substrate side is side-etched during the anisotropic etching process of the semiconductor substrate, so that the anisotropic etching does not reach the electrodes formed on the surface of the semiconductor substrate. During this time, side etching of the semiconductor substrate also progresses, and therefore a through hole is formed which becomes wider on the back side of the substrate.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of an element in each step showing a method of manufacturing a semiconductor device according to an embodiment. In addition, in Figure 1, MESFET
Only the vicinity of the source electrode 3 is shown, and other parts are omitted. Further, the lower side of the figure is the front side of the semiconductor substrate on which MESFETs and the like are formed, and the upper side is the back side of the semiconductor substrate. First, a substrate 1 made of semi-insulating GaAs or the like is prepared, and a semiconductor layer 2 made of GaAs or the like is formed on the surface thereof by epitaxial growth or the like, thereby forming a semiconductor substrate. Then, ME is applied to the surface of the semiconductor substrate, that is, the semiconductor layer 2, by ion implantation, lift-off method, etc.
A S FET is formed. FIG. 1(a) shows this state.

Next, on the back side of the semiconductor substrate, that is, on the substrate 1,
Mask materials are sequentially applied to form a double-layered mask. In other words, magnetron sputtering and EC are applied to the entire back surface.
An insulating film 11 made of SiO2 or the like is deposited by R plasma CVD or the like, and a photoresist film 21 is formed thereon (as shown in FIG. 4B). Thereafter, the photoresist film 21 is selectively left in the portion corresponding to the source electrode 6 by photolithography to form a via hole pattern, and a metal film 12 of Ar, N1, etc. is deposited thereon by vapor deposition or the like. Figure (C) shown).

Next, when the photoresist film 21 serving as a via hole pattern is removed, the metal film 12 thereon is removed, and a second mask pattern is obtained.

Thereafter, when the insulating film 11 is selectively dry etched with CF4 or chlorine gas using the metal film 12 as the second mask pattern as a mask, the first mask pattern corresponding to the second mask pattern becomes the insulating film 11. It is obtained by At this time, the position of the substrate 1 exposed through the openings of the first mask pattern and the second mask pattern is the same as that of the semiconductor layer 2.
This corresponds to the position of the source electrode 3 above (as shown in FIG. 2(d)).

Next, when the semiconductor substrate consisting of the substrate 1 and the semiconductor layer 2 is anisotropically etched using a mixed gas of CC92F2 and Ar as an etchant, the semiconductor substrate 1 is removed in the depth direction (as shown in FIG. 3(e)).

Here, the above etchant is Ga constituting the semiconductor substrate.
It not only has etching ability for As, but also has the first
Since the insulating film 11 such as 8102 that constitutes the mask pattern also has etching ability, the first mask pattern is also side-etched during the process of removing the semiconductor substrate (as shown in FIG. 3(f)). . Therefore, when a through hole is formed in the substrate 1 and the semiconductor layer 2 and the back surface of the source electrode 3 is exposed, the side wall of the through hole has a certain slope (as shown in FIG. 2(g)).

Next, the insulating film 11 and the metal film 12 are etched using a hydrofluoric acid etchant.
TI/Au is removed from the back side of the substrate 1.
is deposited by vapor deposition or the like to form the back conductive film 7. At this time, since the through-hole is formed so as to become wider toward the back side, the back conductive film 7 has a constant thickness even on the side wall of the through-hole (as shown in FIG. 4(h)). Therefore, the source electrode 3 can be well grounded while sufficiently reducing parasitic circuit elements.

In the above embodiments, the degree of inclination of the side wall of the through hole can be arbitrarily set by appropriately selecting the following conditions. First, it can be set depending on the degree of anisotropy of the etchant used; for example, the stronger the anisotropy, the smaller the slope. Next, the degree of inclination can be set depending on the material and thickness of the first mask pattern in contact with the semiconductor substrate.

That is, it is considered that the slope becomes large when the first mask pattern is thick, and also becomes large when the first mask pattern is made of a material that is easily etched. Therefore, by setting the slope of the inner wall of the through hole to a desired value through the above settings and selecting a suitable material and thickness for the back conductive film 7, a good connection between the back conductive film 7 and the source electrode 3 on the front surface can be achieved. It becomes possible.

〔Effect of the invention〕

As described above in detail, in the present invention, the first mask pattern on the substrate side is side-etched during the process of anisotropically etching the semiconductor substrate, so that anisotropic etching is formed on the surface of the semiconductor substrate. Before reaching the etched electrode, side etching of the semiconductor substrate also progresses, and a through hole is formed that becomes wider on the back side of the substrate. Therefore, by depositing a conductive material from the back side of the semiconductor substrate,
Good connection between the electrode on the front surface and the conductive film on the back surface becomes possible. The present invention is suitable for manufacturing high-frequency semiconductor devices because it is possible to sufficiently reduce parasitic circuit elements and ground electrodes on the surface side.

[Brief explanation of drawings]

FIG. 1 is a process diagram of a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a sectional view of a semiconductor device used in a high frequency band, and FIG. 3 is a sectional view showing a conventional method. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Semiconductor layer, 3... Source electrode, 7... Back conductive film, 11... Insulating film (first
mask pattern), 12... metal film (second mask pattern), 21... photoresist film.

Claims (1)

[Claims] A semiconductor substrate having an electrode formed on the front surface is selectively etched from the back side to form a through hole reaching the back side of the electrode, and a conductive material is applied from the back side of the semiconductor substrate. In the method for manufacturing a semiconductor device in which a conductive film is formed on the back surface of the semiconductor substrate, the wall surface of the through hole, and the back surface of the electrode, a first mask material and a second mask material are sequentially applied to the back surface of the semiconductor substrate. a first step of forming first and second mask patterns having openings at positions corresponding to the electrodes; and a first step of forming first and second mask patterns having openings at positions corresponding to the electrodes; and a second step of anisotropically etching the semiconductor substrate through an opening in a second mask pattern to form the through hole, and removing the first and second mask patterns to remove the conductive material. A method for manufacturing a semiconductor device, comprising: a third step of adhering the semiconductor device.