JP2987837B2 - Etching gas and etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an etching gas used for etching a refractory metal and an etching method. INDUSTRIAL APPLICABILITY The present invention can be widely used, for example, in the field of manufacturing semiconductor devices and other electronic components, and in the technical field of etching refractory metals.

[Summary of the Invention]

The etching gas for a high melting point metal of the present invention contains a fluorine-based gas and silane or halosilane, and the method of etching a high melting point metal of the present invention performs etching with the above gas. With such a configuration, etching with high anisotropy can be efficiently achieved, and the occurrence of undercut can be suppressed even during overetching.

[Related Art] In recent years, refractory metals have been used as wiring materials and the like in various fields. For example, tungsten (W) and the like have been used in the field of semiconductor devices such as VLSI. It has become.

Refractory metals are attracting attention due to their properties.For example, tungsten has excellent migration resistance.
In addition, it can be made to have low resistance, and is receiving attention, for example, as a wiring material for future super LSIs.

As a technique for etching a refractory metal, an etching technique having high anisotropy such as RIE is often employed due to a demand for fine processing. As a technique for performing RIE on a high melting point metal, a technique using a fluorine-based gas as an etching gas and a technique using a chlorine-based gas have been conventionally proposed. However, any attempt to RIE chlorine-based gas, for example, tungsten, because of low vapor pressure of WC _x is the reaction product of tungsten and chlorine-based gas, slow etch rate, efficient etching can not be achieved. The RIE Then the tungsten fluoride gas such as SF _6, the etching rate is fast, for reaction with tungsten and fluorine radicals, tungsten from being undercut (Technical Report of IEICE SSD84-45, pp .1-8 (1984)
reference). To reduce the undercut due to SF ₆ ,
Although a method of rapidly and alternately repeating etching by F ₆ and deposition by NH ₃ has been proposed (Extended Abstracts
of the 18th (1986) International Conference on So
lid State Devices and Materials, Tokyo, 1986, pp.229
-232), the equipment and process are complicated and impractical,
Not suitable for mass production.

[Problems to be solved by the invention]

In view of the circumstances described above, the applicant of the present application
-185244, fluorine-based gas and chlorine-based gas, especially SF
Etching gas containing a ₆ and C _2, and proposed an etching method using the same. According to this, high-melting-point metal can be etched at a high speed without using a complicated apparatus or process while suppressing undercut.

However, the technique according to the application has a problem that undercutting occurs in a high melting point metal such as tungsten during overetching. This, WC _x formed as a sidewall protective film is etched by excess fluorine radicals F ^*, it is considered that undercut enters Therefore, undercut occurs during even overetching In any The problem remains.

FIG. 2 shows that a refractory metal portion 12 made of tungsten formed on a semiconductor substrate 11 is formed using a resist 13 as a mask and a gas mixture of SF ₆ / C ₂ at a ratio of 30/28 SCCM. The results are obtained when etching is performed up to etching, and further, 60% over-etching is performed under the same conditions. Here, as the RIE device, a parallel plate type device having a discharge excitation frequency of 13.56 MHz in a cathode coupling system was used, and the power was 0.08 Wcm ⁻² . As is apparent from FIG. 2, the undercut 14 is formed at the base of the high-melting metal portion 12.

Since it is often necessary to perform an over-etching process to some extent for processing the underlayer and other reasons, a technique that does not cause undercutting even during over-etching is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly anisotropic and efficient high-melting-point metal etching technique, and that undercutting does not occur in the high-melting-point metal even during overetching. It is to provide an etching technique.

[Means for solving the problem]

An object of the present invention is to provide an etching gas used for performing over-etching in a reactive ion etching method, for a high melting point metal containing a fluorine-based gas that is a fluoride of nitrogen or a fluoride of sulfur and silane or halosilane at the same time. Is achieved by the etching gas for the reactive ion etching method.

Another object of the present invention is to provide an etching method for etching a refractory metal by a reactive ion etching method, in which a fluorine-based gas that is a fluoride of nitrogen or a fluoride of sulfur and a silane or a halosilane are used at the same time. This is achieved by a reactive ion etching method for refractory metals in which the occurrence of undercuts in etching is suppressed.

In the present invention, as the fluorine-based gas, typically,
Nitrogen fluorides of NF _3, etc., can be mentioned fluorides of sulfur such as SF _6.

In the present invention, silane means silicon hydride and has a composition of Si _n H _{2n + 2} . Typically,
Monosilane SiH ₄ and disilane Si ₂ H ₆ can be exemplified.

In the present invention, halosilane is obtained by replacing at least one hydrogen atom of the above silane with a halogen atom. Preferred halosilanes are those represented by the following general formula.

SiH _n X _m X = C, Br, I, F m = 4 to 1 n = 0 to 3 Typically, SiC ₄ , SiHC ₃ , SiH ₂ C ₂ , SiH ₃ C
Can be mentioned.

At least one of silane and halosilane may be used together with the fluorine-based gas.

(Operation)

When the etching gas of the present invention or the etching method of the present invention is used, undercutting of the refractory metal material is suppressed even during overetching.

Although the mechanism is not always clear, it is because the reaction product of the refractory metal and the silane or halosilane adheres to the side wall as a non-volatile substance, and excess fluorine radicals are removed as silicon fluoride. It is estimated to be.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Needless to say, the present invention is not limited by the following examples.

In this embodiment, the present invention is applied to the manufacture of a semiconductor device.
This is applied to etching of a high melting point metal material 2 (tungsten in this example) formed on a semiconductor substrate 1.

In this example, a 300-nm-thick tungsten layer is formed on the substrate 1 by sputtering (such as direct current sputtering), and this is used as the high melting point material 2 to be etched.

The refractory metal material 2 was etched using a photoresist 3 as a mask by using a usual parallel plate type RIE device (for example, a cathode coupling type having a discharge excitation frequency of 13.56 MHz) under the following conditions.

As a result, a favorable anisotropic shape as schematically shown in FIG. 1 was obtained. In addition, even when over-etching was performed as described with reference to FIG. 2, no undercut was formed.

This is because, in addition to the reaction product of W and SiC ₄ adhering to the side wall as a non-volatile substance, excess fluorine radical F ^* is removed out of the system by the reaction of SiC _x + xF ^* → SiF _x ↑ + xC, It is considered that undercut during overetching was suppressed.

In the above example, the halosilane 1 was used as the Si-containing gas.
The seed, SiC _4, was used, but SiHC ₃ , SiH ₂ C ₂ , SiC
Even when H ₃ C or SiH ₄ is used, the same effect can be obtained because a compound of SiF _x is formed.

Further, in the above embodiment, tungsten is used as the high melting point metal, but it is not limited to this. Tungsten is preferable because it can be selectively grown, but for example, molybdenum or the like may be used and is optional.

As described above, in this embodiment, when dry-etching tungsten, etching was performed using a gas in which SiC ₄ was added to SF ₆ , so that anisotropic processing with good shape could be efficiently achieved, and over-etching was performed. However, the occurrence of undercut can be prevented.

〔The invention's effect〕

As described above, according to the present invention, a fluorine-based gas that is a fluoride of nitrogen or a fluoride of sulfur, and an etching gas for a reactive ion etching method for a high melting point metal containing silane or halosilane, In addition, in the reactive ion etching method, the refractory metal is etched by a gas containing a fluorine-based gas, which is a fluoride of nitrogen or sulfur, and a silane or a halosilane, so that the anisotropic material can be efficiently anisotropically etched. The effect is achieved that the processing can be realized and the undercut at the time of over-etching can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view showing an etching result of one embodiment of the present invention. FIG. 2 is a schematic side sectional view showing an example in which an undercut is made. 2. High melting point metal material (tungsten).

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C23F 4/00 H01L 21 / 3065,21 / 3213

Claims (2)

(57) [Claims] An etching gas used for performing over-etching in a reactive ion etching method, wherein the high-melting point metal includes a fluorine-based gas that is a nitrogen fluoride or a sulfur fluoride, and silane or halosilane at the same time. Etching gas for reactive ion etching method. 2. An etching method for etching a high melting point metal by a reactive ion etching method,
A reactive ion etching method for a high-melting-point metal in which an undercut in over-etching is suppressed by simultaneously using a fluorine-based gas that is a fluoride of nitrogen or a fluoride of sulfur and silane or halosilane.