JPH06132255A - Dry etching method for gate electrode - Google Patents

Abstract

PURPOSE:To reconcile high anisotropy and high selectivity of a gate insulating film by dry-etching the gate electrode of a MISFET, using specified mixed gas. CONSTITUTION:Mixed gas, where Cl2, O2, HCl are mixed at the ratio of 5:1:1, is introduced into ion source by a mass flow controller. Etching is performed, with the gate electrode 11 of a MISFET being a gate electrode 12 as a sample to be processed, by ion beams 18 by discharging electricity at the same time with the introduction. Moreover, the etching processing with this mixed gas also makes the processing of the gate electrode possible in the polycide structure between polysilicon and silicide of high melting point metal, by the simple process of single step even if it is on a stepped face since relatively close etching speeds can be obtained for the silicide and polysilicon.

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 for processing a gate electrode of a MISFET of a semiconductor device, and more particularly to an etching gas therefor.

[0002]

2. Description of the Related Art Anisotropy and selectivity of gate insulator (selection ratio to SiO ₂ ) in plasma processing of gate electrode
It is necessary to raise both of them and make them compatible with each other, and this requirement is becoming stricter year by year. When the gate electrode 11 as shown in FIG. 5 has a polycide structure of the refractory metal silicide electrode 9 and the polysilicon electrode 10 (hereinafter abbreviated as polycide structure), in addition to the silicide and the polysilicon. It is necessary that the etching speeds of the two are close to each other.

In order to achieve both high anisotropy and high selectivity of the gate insulator, conventional etching gases have been disclosed in, for example, JP-A-60-102745 and JP-A-4-67624. As described above, the method using CCl ₄ , CCl ₂ F ₂ , C ₂ Cl ₃ F _3, etc. has been general. However, since these gases cause ozone layer depletion, it has been decided that their use will be completely abolished.

Other techniques which do not use these gases include, for example, JP-A-60-64476 and JP-A-2-94520.
There is a method of using a gas containing Cl such as Cl ₂ and HCl as disclosed in Japanese Patent Laid-Open Publication No. Since it is difficult to achieve both high anisotropy and high selectivity of the gate insulator with a simple substance gas such as Cl ₂ and HCl, it is often used in the form of a mixed gas containing O ₂ and H ₂ . In particular, the method of adding O ₂ is advantageous in processing on the step surface because the etching rate of silicide and polysilicon in the polycide structure becomes close and processing in a single step is possible. But Cl
Just adding O ₂ to _2, both high selectivity of high anisotropy and the gate insulator is not easy, for example, JP-A-2-1552
As disclosed in Japanese Patent Laid-Open No. 30-35321 and Japanese Patent Laid-Open No. 4-105321, it is necessary to devise and improve the etching apparatus itself. Further, for example, Japanese Patent Laid-Open No. 3-62518,
As disclosed in JP-A-3-109719, CF ₄ , CH
_In some cases, an unregulated CFC gas such as ₂ F ₂ is added, but the exhaust gas after plasma etching contains a specified CFC gas to be regulated.

As other gas, for example, JP-A-3-1278
No. 26, M. Nakamura et.al. Proc. Of Symposium on D
HBr, as disclosed in ry Process P58 (1988),
A gas containing Br such as Br ₂ is used. In this case as well, it is often used in the form of adding O ₂ or the like, like the Cl-based gas.
However, when the gate electrode has the polycide structure as described above, the refractory metal silicide can hardly be etched with the Br-based gas. In this case, for example, Tatsumi et al., 37th Joint Symposium on Applied Physics, 28p-
As with ZF-3, it is necessary to add SF ₆ gas or perform multi-step processing with other gas systems.

[0006]

The conventional techniques have the above-mentioned problems. The issues will be summarized below. Gases such as CCl ₄ , CCl ₂ F ₂ and C ₂ Cl ₃ F ₃ that have been generally used cause ozone layer depletion, and it has been decided that the use will be completely abolished.

Gases based on Cl ₂ or HCl have the drawback that it is difficult to achieve both high anisotropy and high selectivity of the gate insulator. The gas based on HBr has a very high selection ratio with respect to the photoresist and the gate insulator, and at the same time satisfies the high anisotropy. In the case of the polycide structure, since the refractory metal silicide can hardly be etched, it is necessary to perform multi-step etching, and the multi-step etching has a drawback that it is difficult to process the step. Further, there is a drawback that the redeposited residue of the reaction product remains in a form that is very difficult to remove.

The present invention has been made to solve the above problems and to provide a dry etching method capable of achieving both high anisotropy and high selectivity of a gate insulator.

[0009]

According to the present invention, (1) in a dry etching process for processing a gate electrode of a MISFET of a semiconductor device, Cl ₂ , O ₂ , and hydrogen halide are each used as an etching gas in an amount of about 5: 1: A dry etching method for a gate electrode characterized by using a gas mixed in a ratio of 1; and (2) a case where the gate electrode has a polycide structure of polysilicon and a refractory metal silicide (1 (3) The dry etching method according to (1) or (2), wherein the hydrogen halide is (3) hydrogen chloride.

[0010]

In the present invention, hydrogen halide gas is added to the conventional method of etching with Cl ₂ / O ₂ gas system,
The gate electrode is dry-etched with a gas in which Cl ₂ , O ₂ and hydrogen halide (HCl, HBr, etc.) are mixed at about 5: 1: 1.

According to the present invention, by slightly adding HCl to Cl ₂ / O ₂ , the selectivity of the gate insulator is improved, the high anisotropy in the etching process and the selectivity to SiO ₂ are improved.

[0012]

EXAMPLES The present invention will be described below with reference to Examples of the present invention.
The action and effect of will be described together. ECR etch shown in Figure 3
Was used. Cl in MFC 4 in the ion source₂, O
₂ Introduce a mixed gas containing HCl and HCl in a prescribed composition and discharge.
The ion beam 18 causes the structure shown in FIG.
The gate electrode 11 of the MISFET whose underlayer is the gate oxide film 12.
As the sample 5 to be processed, etching processing was performed.

Electrode temperature -20 ° C, 1 mTorr, gas flow rate 40sc
FIG. 2 shows the etching rate of polysilicon and the selectivity to SiO ₂ when Cl ₂ / O ₂ gas system and HCl / O ₂ gas system were etched under the condition of cn.
Shown in (a) and (b). In both cases, when the amount of O ₂ added exceeds 15%, the polysilicon etching rate decreases, and when it exceeds 20%, the etching of polysilicon does not proceed. Vs. SiO ₂ selectivity ratio towards the gas system of Cl ₂ / O ₂ is higher than the gas system of the HCl / O _2, increases as increasing the amount of O _2. From these, it is appropriate to add O _{2 in} an amount of 10 to 15% of the total amount.

Under the conditions of electrode temperature -20 ° C. and 1 mTorr, C
FIG. 1 shows the etching rate of polysilicon and the selectivity to SiO ₂ when HCl was added to a gas of 1 ₂ 30 sccn + O ₂ 6 sccn. Even if the amount of HCl added increases, if it is 20% or less, the polysilicon etching rate remains almost unchanged. However, the selectivity to SiO ₂ improves even with a small addition of HCl. At this time, the anisotropy of etching is slightly improved. However, when it is added in an amount of 20% or more of the total, the etching rate is remarkably lowered (not shown in FIG. 1, the selection ratio to photoresist is also remarkably lowered). From these H
It is appropriate that the amount of Cl added be 10 to 20% of the total amount.

Further, FIG. 1 shows the data when the electrode temperature is −20 ° C., but at room temperature, the effect of this HCl addition becomes small. The present invention is extremely effective in the case of low temperature etching. Although the case where HCl is added to the Cl ₂ / O ₂ gas system has been described above, the same effect can be obtained when another hydrogen halide such as HBr is added. In the case of HBr and HCl, the former is more effective in improving the anisotropy and the selectivity to SiO ₂ . As when using a gas system of HBr / Cl ₂ / O ₂ may JP 3-241829. The characteristics shown in the examples of Japanese Patent Application Laid-Open No. 3-241829 differ greatly from those of the present patent, but the electrode temperature is about 1
Because there is a difference of 00 ℃. However, when HBr is added, make sure that no etching residue (reaction product) remains.
It is necessary to adjust other parameters.

Further, when the etching process is performed in this gas system at this gas ratio, the gate electrode having the polycide structure can obtain a relatively close etching rate between silicide and polysilicon. It is possible to process with a simple process.

[0017]

According to the present invention, it is possible to achieve both high anisotropy and a high selection ratio of a gate insulator in the processing of a gate electrode of a MISFET using a conventional dry etching apparatus. Facilitates processing. Furthermore, the process using the present invention is a safe process that does not require a specific CFC gas or halon gas, and does not discharge them as exhaust gas.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between HCl concentration and etching characteristics in a Cl ₂ / O ₂ gas system.

FIG. 2 is a characteristic diagram showing a relationship between O ₂ concentration in Cl ₂ and HCl gas and etching characteristics.

FIG. 3 is a schematic explanatory diagram of an ECR etching apparatus.

FIG. 4 is a structural cross-sectional view of a MOSFET gate electrode.

FIG. 5 is a cross-sectional view of a polycide structure of a gate electrode.

[Explanation of symbols]

 1 Electromagnetic coil 2 Quartz window 3 Microwave (2.45GHZ) 4 Mass flow controller 5 Workpiece sample 6 Exhaust hole 7 Cooling water 8 Si substrate 9 Refractory metal silicide electrode 10 Polysilicon electrode 11 Gate electrode 12 Gate oxide film 13 LOCOS film 14 Photoresist 15 Ion beam

Claims (3)

[Claims] 1. A semiconductor device MISFET (Metal Insulator S
In the dry etching process for processing the gate electrode of the semiconductor field effect transistor, a gas characterized by using Cl ₂ , O ₂ and hydrogen halide mixed at a ratio of about 5: 1: 1 is used as the etching gas. Electrode dry etching method. 2. The dry etching method according to claim 1, wherein the gate electrode has a polycide structure of polysilicon and silicide of refractory metal. 3. The dry etching method according to claim 1 or 2, wherein the hydrogen halide is hydrogen chloride.