JPH04340716A - Dry etching method - Google Patents

Abstract

PURPOSE:To prevent the generation of undercut at the time of overetching when a silicon based thin film or high melting point metal polycide structure is etched. CONSTITUTION:When a multilayered film formed by laminating a doped polysilicon film 12 and a tungsten silicide film 13 in order on an SiO2 film 11 on a silicon substrate 10 is etched, the tungsten silicide film 13 is etched by using SF6 and HBr, and then the doped poly silicon film 12 is etched by using HBr. When the base SiO2 film 11 begins to be exposed, overetching is performed by adding SiBr4 to HBr. As the result of adding SiBr4 at the time of overetching, the state that SiBr4 adheres to the side wall of a doped poly silicon film 12 is maintained, and the effect protecting the side wall can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method used in the manufacturing process of semiconductor devices.

0002

[Prior Art] In recent years, ULSI (ultra lar
With the increase in speed of devices (ge scale integration), for example, tungsten polycide (W-polycide), which is a laminated film of doped polysilicon (DOPOS) and an upper layer of tungsten silicide (WSiX), is being used as a transistor gate structure.
) is being adopted.

[0003] As for the etching method of such tungsten polycide, the spring 1990; Proceedings of the Japan Society of Applied Physics, p. 28-
The method described in ZF-3 is known. This method is a gas-based etching process that does not use CFCs.
Etching is performed using sulfur hexafluoride (SF6) and hydrogen bromide (HBr) using an F bias application type ECR plasma etcher, and the sidewalls are protected by deposits (SiBr4) caused by the addition of HBr. This means that anisotropic processing becomes possible.

In addition, tungsten silicide (WSi)
Two-step etching is known in which doped polysilicon (DOPOS) is etched using HBr after etching X) using SF6+HBr.

[0005] In the above-mentioned conventional technology, for example, as shown in FIG. 4, a doped polysilicon (DOPOS) film 3 and a tungsten silicide (WSiX) film 4 are sequentially formed on a SiO2 film 2 formed on the surface of a silicon substrate 1. A resist 5 of a desired pattern is patterned on the laminated tungsten polycide structure, and this resist is used as a mask.
Sequentially WSiX film 4, DOPOS film 3, SF6+HBr,
The plan is to perform etching using HBr.

[0006]

[Problems to be Solved by the Invention] However, when etching is proceeded using such a conventional method, until the just-etched state as shown in FIG. However, during over-etching to ensure the removal of the DOPOS film 3, the supply of Si that forms SiBr4 is lost (this is because the DOPOS film disappears, and the Si that forms SiBr4 is removed from the underlying SiO2 film). ), DOPOS as shown in Figure 6
The problem arises that the membrane 3 is undercut.

The present invention was devised in view of these conventional problems, and aims to provide a dry etching method that does not cause undercuts during overetching of polycide structured films and silicon-based thin films. It is something to do.

[0008]

SUMMARY OF THE INVENTION Accordingly, the first means of the present invention is to perform over-etching using a gas containing at least SiBr4 in a dry etching method for a silicon-based thin film.

[0009] Furthermore, in the dry etching method of a laminated film of a silicon-based thin film and a high melting point metal silicide thin film,
A second solution is to perform over-etching using a gas containing at least SiBr4.

0010

According to the first aspect of the invention, when a silicon-based thin film is over-etched, by supplying a gas containing SiBr4, SiBr4 adheres to the sidewalls of the silicon-based thin film, thereby preventing the occurrence of undercuts.

In the invention of claim 2, a protective film made of SiBr4 is also formed on the side wall of the silicon-based thin film that is the lower layer film of the high melting point metal silicide thin film during over-etching, as in the invention of claim 1. , anisotropic processing becomes possible.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the dry etching method according to the present invention will be explained below based on the embodiments shown in FIGS. 1 to 3.

First, as shown in FIG.
A doped polysilicon (DOPOS) film 12 as a silicon-based thin film is deposited on the SiO2 film 11 formed on the
After deposition by the VD method, a tungsten silicide (WSiX) film 13 is laminated thereon to form a tungsten polycide structure. Then, a resist is patterned on the tungsten silicide film 13.

Next, the tungsten silicide film 13 is etched under the following etching conditions.

○ Etching gas and its flow rate Sulfur hexafluoride (SF6)...15SCCM Hydrogen bromide (HBr)...3
5SCCM ○Pressure 5mTorr ○Microwave current 250mA ○RF bias 150W Next, the doped polysilicon film 12 is etched under the following etching conditions.

○ Etching gas and its flow rate Hydrogen bromide (
HBr)...50SCCM ○Pressure 5mTorr ○Microwave current 250mA ○RF bias 200W When etching the doped polysilicon film 12, due to the addition of HBr as an etching gas, SiB
A sidewall protective film 12a made of rX is formed.

Thereafter, from the state where the underlying SiO2 film 11 begins to be exposed, over-etching is performed by switching to the etching conditions described below.

○ Etching gas and its flow rate Hydrogen bromide (
HBr)...40SCCM SiBr4...10SCCM ○Pressure 5mTorr ○Microwave current 250mA ○RF bias 200W In this way, by adding SiBr4 to the etching gas during over-etching, SiBr4 adheres to the sidewall of the doped polysilicon film 12. , the occurrence of undercuts is prevented. When etching is performed only with HBr without adding SiBr4, the sidewall protective film 12a
The SiBr4 forming the surface is detached from the side wall, resulting in an undercut. Furthermore, since Si in the underlying SiO2 film 11 is strongly bonded to oxygen, it does not form SiBr4 with Br in HBr.

The present invention has been explained above by applying the present invention to a tungsten polycide structure, which is a laminated film of a silicon-based thin film and a refractory metal silicide thin film, but when a silicon-based thin film is etched and further over-etched, ,
The invention can be widely applied.

In the above embodiment, etching was performed in three steps: etching of the tungsten silicide film 13, etching of the doped polysilicon film 12, and over-etching. SiBr4 may also be added.

Furthermore, in order to promote the formation of the sidewall protective film, oxygen (O2) and nitrogen (N2) are added during overetching.
) etc. may be added to form SiOX, SiN, etc. on the side walls.

[0022]

[Effects of the Invention] As is clear from the above explanation, according to the dry etching method of the present invention, it is possible to prevent undercuts from occurring in silicon-based thin films during over-etching, and to perform good anisotropic processing. effective.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing steps in an embodiment of the present invention.

FIG. 2 is a sectional view showing steps in an embodiment of the present invention.

FIG. 3 is a sectional view showing steps in an embodiment of the present invention.

FIG. 4 is a sectional view showing a conventional process.

FIG. 5 is a sectional view showing a conventional process.

FIG. 6 is a sectional view showing a process of a conventional example.

[Explanation of symbols]

11... SiO2 film, 12... Doped polysilicon film, 1
2a...Side wall protective film, 13...Tungsten silicide film.

Claims (2)

[Claims] 1. In a dry etching method for a silicon-based thin film, over-etching is performed using at least SiBr.
A dry etching method characterized in that it is carried out using a gas containing 4. 2. A dry etching method for a laminated film of a silicon-based thin film and a refractory metal silicide thin film, characterized in that over-etching is performed using a gas containing at least SiBr4.