JPH05267240A - Method for dryetching tungsten silicide film - Google Patents

Abstract

PURPOSE:To obtain an etching method which generates no undercuts under a photoresist film and provides a high selectivity ratio with a silicon oxide film in etching a tungsten silicide film. CONSTITUTION:A tungsten silicide film 3 is etched by reactive etching by using the mixture gas of SF6, HBr, and O2 or that of SF6, HBr, O2, and N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of dry etching a tungsten silicide film, and more particularly to a method of dry etching a tungsten silicide film in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art With the recent high integration and high speed of LSI, the wiring material has been changed from a polysilicon film to a tungsten silicide film. This is because the tungsten silicide film has a lower layer resistance and the contact portion has a lower resistance than the polysilicon film.

Further, in the gate wiring, a laminated structure of a tungsten silicide film and a polysilicon film has come to be used in order to have a low resistance and stable MOS structure. As an etching technique for forming these wirings and electrodes, an anisotropic shape that does not cause undercut can be obtained even in a single layer of a tungsten silicide film or in a stack of a tungsten silicide film and a polysilicon film. Is required.

A reactive ion etching (hereinafter referred to as RIE) method is mainly used for the conventional etching of the tungsten silicide film. As the reaction gas, Freon gas (compound composed of C, H, Cl, F such as CF ₄ and CCl ₂ F ₂ ), sulfur hexafluoride (SF ₆ ), mixed gas of Freon gas and SF ₆ is used. Further, a mixed gas of Freon gas and O ₂ is used. In addition, E.R.White and others are published by Journal of the Electrochemical Society (J
individual of the Electrochem
129, pp. 1330 (1)
(982), a mixed gas of CF ₄ and O ₂ was used.

[0005]

Of the etching gases for the conventional tungsten silicide film described above, the CFC gas, SF ₆ and the mixed gas of CFC gas and SF ₆ have a low selectivity with respect to the oxide film, and therefore are shown in FIG. As described above, when the tungsten silicide film 3 is etched using the photoresist film 4 as a mask, the silicon oxide film 2 under the tungsten silicide film 3 is not etched either. Further, as shown in FIG. 7, in the etching of the tungsten silicide film 3A in the two-layer structure of the tungsten silicide film 3A and the polysilicon film 6 (hereinafter, referred to as polycide structure), the polysilicon film 5 is undercut during overetching. There is a problem that the undercut portion 6 is formed. This is because the fluorine-based radicals etch the polysilicon film 5 isotropically, and the etching rate of the polysilicon film 5 is higher than that of the tungsten silicide film 3A.

Next, the mixed gas of Freon gas and O ₂ has a problem that an undercut portion 6A is formed in the tungsten silicide film 3 as shown in FIG. Moreover, of the above CFCs, CFCs (CFCs 11 and 1)
Fluorocarbons containing three elements of C, Cl and F, such as 2,113, 114 and 115, also have a problem of environmental destruction that destroys the ozone layer in the stratosphere.

Recently, HB having a highly anisotropic etching characteristic is used as an etching gas for a tungsten silicide film.
A process using a mixed gas of r and SF ₆ is described by Tetsuya Tatsumi et al., Spring 1990, Proceedings of the Japan Society of Applied Physics, 28P-2.
Reported in F-3. However, in the etching of the tungsten silicide film using the mixed gas of HBr and SF ₆ , there is a problem that the lower oxide film is etched as shown in FIG. 6 because the selectivity with respect to the oxide film is low.

[0008]

The dry etching method of the tungsten silicide film of the present invention According to an aspect of the mixing of the etching gas, a mixed gas of SF ₆ and HBr and O _2, or SF ₆ and HBr and O ₂ and N _2, It uses gas.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor chip for explaining the first embodiment of the present invention.

First, a silicon oxide film 2 is formed on a silicon substrate 1.
And a tungsten silicide layer 3 for wiring, which is an object to be etched, is formed thereon by a sputtering method. After that, the photoresist film 4 as a mask is formed by using the lithography technique.

Next, the tungsten silicide film 3 is formed into SF ₆
Etching was performed by the RIE method using a mixed gas containing HBr and O ₂ gas to form wiring. The etching conditions at this time are as follows: pressure ₆ Pa, RF power 600 W, SF ₆ flow rate 20 SCCM, HBr flow rate 30 SCCM, O ₂ flow rate 1
It is 0 SCCM.

It is desirable that the ratio of the HBr flow rate to the HBr flow rate and the SF ₆ flow rate is 0.2 to 5.0%. When the HBr flow rate is 0.2% or less, the tungsten silicide film 3 has an undercut portion. On the other hand, when the HBr flow rate is 5.0% or more, the etching rate is lowered, which is not practical. The O ₂ flow rate is preferably 5 to 30% of the total flow rate. O ₂ flow rate is 30%
In the above case, an undercut portion is formed in the tungsten silicide layer and the selectivity to the silicon oxide film is lowered when the content is 5% or less.

[0013] The relationship between the etching rate and the O ₂ flow rate of the tungsten silicide film in FIG. 3, also shown in FIG. 4 the relation between the selection ratio and the O ₂ flow rate of the tungsten silicide film.
It can be seen from FIGS. 3 and 4 that the addition of O ₂ to the etching gas increases the etching rate of the tungsten silicide film and also increases the selection ratio with respect to the silicon oxide film and the photoresist film.

2A and 2B are sectional views of a semiconductor chip for explaining a second embodiment of the present invention, showing the case where the present invention is applied to polycide wiring.

First, as shown in FIG. 2A, a silicon oxide film 2 is formed on a silicon substrate 1, and a polysilicon film 5 is grown on the silicon oxide film 2. After that, a tungsten silicide film 3A that is an object to be etched is formed by a sputtering method, and a photoresist film 4 that serves as a mask is formed thereon by using a lithography technique.

Next, the tungsten silicide film 3A is formed into a first layer.
In the same manner as in Example 1, etching is performed by the RIE method using a mixed gas containing SF ₆ , HBr and O ₂ gas. Here, the etching of the tungsten silicide film 3A is 50
Even if over-etching, the shape is not damaged.

Next, as shown in FIG. 2B, the polysilicon film 5 is subjected to RIE using a mixed gas of HBr, Cl _{2 and the} like.
Method is used to form polycide wiring. As described above, according to the second embodiment, the polycide wiring can be formed without forming an undercut portion in the polysilicon film as in the conventional case.

Next, a third embodiment of the present invention will be described. In the third embodiment, SF ₆ , HBr, O ₂ and N ₂ gases are used as a gas for etching the tungsten silicide film having the structure shown in FIGS. The etching conditions are, for example, a pressure of 6 Pa and an RF power of 600.
W, SF ₆ flow rate 20 SCCM, HBr flow rate 30 SCC
M, O ₂ flow rate 10 SCCM and N ₂ flow rate 10 SCCM. The addition of N ₂ is for improving the in-plane uniformity of the wafer, and the N ₂ flow rate is desired to be 5% to 40% of the total flow rate. If it is less than 5%, the effect of adding N ₂ is small, and if it is more than 40%, the shape of the tungsten silicide film becomes a forward tapered shape, which is not preferable.

FIG. 5 shows the relationship between the in-plane uniformity of the etching rate of the tungsten silicide film on the wafer and the N ₂ flow rate. Here, if the maximum value, the minimum value, and the average value of the etching rate are respectively set as R _Max , R _Min , and R _M , the uniformity is defined as (R _Max −R _Min ) / 2R _M. As can be seen from FIG. 5, by adding N ₂ gas, the first
It can be seen that the uniformity is improved as compared with the example. S
The etching using F ₆ , HBr, O ₂ and N ₂ gas can be applied to the formation of the tungsten silicide wiring and the polycide wiring as in the first and second embodiments.

[0020]

As described above, the present invention has the following effects because the mixed gas of SF ₆ , HBr and O ₂ is used as the etching gas for the tungsten silicide film in the manufacturing process of the semiconductor device.

First, it is possible to obtain an etching shape without undercut. Secondly, by increasing the O ₂ flow rate, the selection ratio between the oxide film and the photoresist film can be improved. Thirdly, in the etching of the tungsten silicide film having the polycide structure, since the etching rates of the tungsten silicide film and the polysilicon film can be made substantially the same, the polysilicon film can be etched vertically without causing an undercut.

Further, by adding N ₂ to the mixed gas of SF ₆ , HBr, and O ₂ , there is an effect that the uniformity of the etching rate within the wafer surface can be improved in addition to the above effect. ..

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip for explaining a first embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor chip for explaining a second embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an O ₂ flow rate and an etching rate.

FIG. 4 is a diagram showing a relationship between an O ₂ flow rate and a selection ratio.

FIG. 5 is a diagram showing a relationship between N ₂ flow rate and uniformity.

FIG. 6 is a sectional view of a semiconductor chip for explaining a conventional example.

FIG. 7 is a cross-sectional view of a semiconductor chip for explaining a conventional example.

FIG. 8 is a cross-sectional view of a semiconductor chip for explaining a conventional example.

[Explanation of symbols]

 1 Silicon substrate 2 Silicon oxide film 3,3A Tungsten silicide film 4 Photoresist film 5 Polysilicon film 6,6A Undercut part

Claims (4)

[Claims] 1. A dry etching method for a tungsten silicide film formed on a semiconductor substrate via an insulating film or a polysilicon film, wherein sulfur hexafluoride (SF ₆ ), hydrogen bromide (HBr) and oxygen are used as etching gases. (O
A dry etching method for a tungsten silicide film, which comprises using the mixed gas of ₂ ). 2. The ratio of hydrogen bromide to sulfur hexafluoride is 0.2 to 5%, and the ratio of oxygen to the total amount of gas is 5.
The dry etching method for a tungsten silicide film according to claim 1, wherein the dry etching method is about 30%. 3. The dry etching method for a tungsten silicide film according to claim 1, wherein the etching gas is sulfur hexafluoride, hydrogen bromide, oxygen and nitrogen (N ₂ ). 4. The ratio of nitrogen to the total amount of gas is 5 to 40.
The dry etching method for a tungsten silicide film according to claim 3, wherein