JPH0722391A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable a multilayered film etching process, wherein fluorine gas plasma etching and halogen gas (excluding fluorine gas) plasma etching are successively executed in this sequence, to be enhanced in reproducibility and stability. CONSTITUTION:A dry etching method is composed of a first process wherein fluorine-containing gas introduced into a chamber is turned into plasma to etch the surface of a tungsten silicide 13 and a second process wherein halogen- containing gas except fluorine introduced into the chamber and set to a pressure range of 0.5 to 5mTorr is turned into plasma to etch the surface of a polycrystalline silicon 12. By this setup, an electron deposition phenomenon caused by fluorine element can be restrained from occurring, so that an etching operation can be improved in reproducibility of etching rate, selection ratio, shape, and others.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for finely processing a thin film by plasma etching.

[0002]

2. Description of the Related Art Advances in high-density semiconductor integrated circuits are bringing about changes comparable to the industrial revolution. Higher densities have been realized by miniaturization of device dimensions, improvement of devices, and enlargement of chip size. The miniaturization of device dimensions has advanced to about the wavelength of light, and the use of excimer lasers and soft X-rays is being considered for lithography. Along with lithography, dry etching plays an important role in realizing fine patterns.

The dry etching is a processing method for removing an unnecessary portion of a thin film or a substrate by utilizing a chemical or physical reaction on a gas-solid phase surface by plasma, radicals, ions and the like. The most widely used dry ion etching technology is reactive ion etching (RI
E) is that when a sample is exposed to a high-frequency discharge plasma of an appropriate gas, an unnecessary portion of the sample surface is removed by an etching reaction. The required portion is usually protected by the photoresist pattern used as a mask.

FIG. 5 is a schematic view showing a typical reactive ion etching apparatus having parallel plate electrodes. A reactive gas is introduced into the metallic chamber 1 through a gas controller 2, and an exhaust system 3 controls the reactive gas to an appropriate pressure. The pressure in chamber 1 is usually 100 to 10
Set to 00 mTorr. An anode (anode) 4 is provided above the chamber 1, and a sample table 5 serving as a cathode (cathode) is provided below the chamber 1. On the sample table 5,
An RF power source 7 is connected via an impedance matching circuit 6, and high frequency discharge can be generated between the sample stage 5 and the anode 4.

Various types of films are used in semiconductor integrated circuits, and they must be microfabricated to have the required size and shape. One of the processes that requires high dimensional accuracy is gate electrode processing. Since the size of the gate electrode is an important parameter that determines the operating speed of the device and the driving force of the circuit, only a size change of 10% or less from the design size is allowed. Since the minimum size is usually applied to the gate electrode in order to increase the operation speed of the device, it can be said that this is the process that requires the finest and most accurate dimensional accuracy.

For the purpose of lowering electric resistance, a high melting point metal silicide represented by a tungsten silicide film and a so-called polycide film which is a phosphorus-doped polycrystalline silicon film as a lower layer have begun to be used for the gate electrode in recent years. In etching such a two-layer film, each film is usually etched using two or more different gases using the dry etching apparatus as described above.
For example, CF is used for etching the tungsten silicide film.
Plasma of gas containing fluorine such as ₄ and SF ₆ is used,
For etching the polycrystalline silicon film, Cl ₂ , HCl, H
Plasma of halogen gas or halogen compound gas other than fluorine such as Br is used. When the tungsten silicide film is etched, reaction products with a high vapor pressure such as SiF ₄ and WF ₆ are formed, and when the polycrystalline silicon film is etched, reaction products with a high vapor pressure such as SiCl _x are generated, and the etching proceeds by evacuation. Pressure is from 100mTorr to 1000
mTorr, input power of about 200 to 500 W is used, and etching rate is 200 to 300 nm / min.
The degree is obtained.

In addition to this example, etching with a halogen-based gas other than fluorine is often performed after etching with a fluorine-based gas in the semiconductor element manufacturing process. For example, a structure in which a silicon oxide film is placed on the gate electrode may be formed. In this case, a fluorine-based gas such as CF ₄ or CHF ₃ is used for etching the silicon oxide film, and for etching the gate electrode. For example, chlorine gas is used.

[0008]

A multilayer film structure can be etched by such two-step etching, but when applied to an actual trial production line, there arises a problem that etching characteristics such as etching rate, shape, and selection ratio are not stable. Came.

FIG. 6 shows the dependence of the etching rate of the polycrystalline silicon film in the etching of tungsten polycide and the selection ratio to the oxide film on the number of processed wafers. Etching rate of 20 to 4 when etching several wafers
It can be seen that it decreases by 0%, and the selection ratio to the oxide film decreases to about 50%. The etching conditions at this time were as follows. The first step is to use CF4 gas at a pressure of 20.
0mTorr, RF power (13.56MHz) 400W
I went there. The second step uses HBr and Cl ₂ gas, pressure 150 mTorr, RF power (13.56 MH).
z) Performed at 250W. In both cases, the stage temperature is 20 ° C.
And As a result of examining the cause, it was concluded that the fluorine component remaining in the chamber had an influence on the plasma. That is, fluorine has the highest electronegativity among halogen elements, and easily becomes negative ions in plasma due to an electron attachment phenomenon. This is because the electron consumption consumes electrons and the ion generation rate is reduced, which reduces the radicals of Cl and Br and the ion density. Similar phenomena occur in Hemker et al. (Electrochemical Society, Spring Meeting, Honolulu,
Abstract p. 360-361, 1993).

Since this is a phenomenon caused by the fluorine remaining in the chamber, it is considered that such instability can be reduced by performing the two etching steps in different chambers. However, preparing two chambers causes a significant increase in cost, and if they are used as one device having a so-called multi-chamber, there is a concern that the operating rate of the device may decrease. When the two devices are separately operated, the cost of the device is increased, and in addition, a dead time and a waste of labor are required due to the movement of the wafer, resulting in an extremely high cost.

In view of the above problems, the present invention is a highly accurate dry etching that can stably reproduce parameters such as etching rate when etching is performed with a halogen-based gas other than fluorine after etching with a fluorine-based gas. It provides a method.

[0012]

In order to solve the above-mentioned problems, the dry etching method of the present invention comprises a first step of introducing a gas containing fluorine into a chamber to generate plasma and etch the sample surface, A gas containing halogen element other than fluorine is introduced into the chamber and the pressure is set to 0.05P.
A second step of etching the sample surface by generating plasma in the range of a to 5 Pa is provided.

[0013]

According to the present invention, even if fluorine remains in the chamber in the above-mentioned first step, the etching parameters can be stably reproduced with almost no influence of the residual fluorine at the pressure in the second step. It is generally known that under the pressure of several Pa or less, the electron attachment phenomenon decreases as the pressure decreases. This is because the density of the halogen element itself such as fluorine causing adhesion decreases with pressure and the electron temperature increases with pressure decrease, so the ratio of low energy-electrons contributing to electron adhesion to the total number of electrons decreases. This is because. In the case of SF6 plasma, the pressure around 100 mTorr is a so-called electronegative plasma in which the number of positive ions is 100 per electron, but it is 1 mTorr.
Below this, the number of positive ions is approximately 1 for 1 electron, and the electron attachment phenomenon does not affect the plasma.

Pressure from 0.5 mTorr to 30 mTorr
By setting it in the range of r, the directivity of ions is improved at the same time, and the anisotropy of etching itself is also improved. Therefore, H
It is not necessary to add a gas such as Br for forming the side wall protective film, and it is expected that the yield is improved by reducing the generation of particles.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The dry etching method of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a manufacturing process for explaining a dry etching method according to the first embodiment of the present invention.

First, as shown in FIG. 1a, a silicon substrate 10,
Gate oxide film 11, phosphorus-doped polycrystalline silicon film 12
On the sample surface consisting of
A photoresist pattern 14 that functions as a mask during dry etching is formed.

In FIG. 1b, the silicon substrate 10 thus prepared is used for Lissajous electron plasma (LE).
P) Etched with an etcher. Lissajous electron plasma etching (Okuni et al., VLSI Technology Symposium, Digest of Technical Papers, p. 151, 1993) is a technique for etching a plasma generated by forming a rotating electric field in a chamber. The feature is that it can be etched in a high vacuum. The etching conditions for the first step tungsten silicide are CF ₄ gas 50
The sccm, the pressure was 7.5 mTorr, the high frequency power to the LEP3 electrode was 100 W × 3 (50 MHz), and the RF bias power was 50 W (13.56 MHz).

Subsequently, in FIG. 1c, the etching conditions for the polycrystalline silicon in the second step are Cl ₂ gas 40 sccm,
Pressure 7.5mTorr, high frequency power to LEP3 electrode 8
0Wx3 (50MHz), RF bias power 50W (1
3.56 MHz).

The etching rate of polycrystalline silicon is about 310 n.
At m / min and an oxide film selection ratio of about 80, as shown in FIG. 2, no dependence on the number of processed wafers was observed.

Next, a dry etching method according to the second embodiment of the present invention will be described. 3A to 3D are sectional views of manufacturing steps for explaining the dry etching method in the first embodiment of the present invention.

First, as shown in FIG. 3a, a silicon substrate 10,
Gate oxide film 11, phosphorus-doped polycrystalline silicon film 12
Then, a photoresist pattern 14 that functions as a mask during dry etching is formed on the surface of the sample composed of a silicon oxide film 15 formed by atmospheric pressure CVD.

In FIG. 3b, the silicon substrate 10 thus prepared is subjected to EC using the electron cyclotron resonance phenomenon.
Etched with R etcher. The ECR etcher can also be etched in a higher vacuum than the parallel plate RIE. The etching conditions of the silicon oxide film 15 in the first step were C ₄ F ₈ gas 30 sccm, pressure 1 mTorr, microwave power 1.2 KW (2.45 GHz), and RF bias power 200 W (2.5 MHz).

Subsequently, in FIG. 3c, the etching conditions for the polycrystalline silicon in the second step are Cl ₂ gas 30 sccm,
The HBr gas was 2 sccm, the pressure was 2 mTorr, the microwave power was 1.2 KW (2.45 GHz), and the RF bias power was 50 W (2.5 MHz). The etching rate of polycrystalline silicon is about 200 nm / min, and the selection ratio to oxide film is about 50.
Therefore, as shown in FIG. 4, the dependency on the number of processed wafers was not found.

In the example, the gas used in the second step is Cl ₂ or Cl ₂ to which another gas is added. However, instead of Cl ₂ , HCl, HBr, Br ₂ ,
It goes without saying that the effects of the present invention can be obtained even with a gas such as HI or a gas obtained by adding another gas to them. Although the case where the gas containing fluorine is CF4 and C4F8 is shown, it goes without saying that the effect of the present invention can be obtained even if the gas contains C and F or a compound of C, H, F.

[0026]

As described above, according to the dry etching method of the present invention, the first step of introducing a gas containing fluorine into the chamber to generate plasma to etch the sample surface and the chamber containing a halogen element other than fluorine are included. Good reproducibility of etching rate, selection ratio, shape, etc. by adopting a configuration including a second step of etching the sample surface by introducing plasma with a gas pressure of 0.5 mTorr to 5 mTorr. It can be done.

[Brief description of drawings]

FIG. 1 is a sectional view of a manufacturing process for explaining a dry etching method according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining changes over time in the etching rate in the dry etching method according to the first embodiment of the present invention.

FIG. 3 is a manufacturing step sectional view for explaining a dry etching method which is a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the change over time in the etching rate in the dry etching method according to the second embodiment of the present invention.

FIG. 5 is a block diagram of a conventional parallel plate dry etching apparatus.

FIG. 6 is a diagram for explaining the change over time in the etching rate in the conventional parallel plate dry etching method.

[Explanation of symbols]

 10 Silicon substrate 11 Gate oxide film 12 Phosphorus-doped polycrystalline silicon film 13 Tungsten silicide film 14 Photoresist pattern 15 Silicon oxide film

Claims (5)

[Claims] 1. A first step of introducing a gas containing fluorine into a chamber to generate plasma to etch a sample surface, and a gas containing a halogen element other than fluorine is introduced into the chamber and the pressure is changed from 0.5 mTorr to 30 mTorr.
a second step of etching the sample surface by generating plasma in the range of r. 2. A gas containing a halogen element other than fluorine,
The dry etching method according to claim 1, wherein the gas is a gas containing any one of Cl ₂ , HCl, HBr, Br ₂ , and HI. 3. The gas containing fluorine is C, F or C,
The dry etching method according to claim 1, wherein the gas is a gas containing a compound of H and F. 4. The dry etching method according to claim 1, wherein plasma is generated in the chamber by using a rotating electric field. 5. The dry etching method according to claim 1, wherein the sample to be etched contains a tungsten film or a tungsten silicide film, and a silicon film.