JPH06283477A - Method of manufacturing semiconductor device - Google Patents

Abstract

PURPOSE:To etch anisotropically and at a high speed and extremely readily remove resist used as a mask when a polysilicon film on an insulation film is dry-etched. CONSTITUTION:In order to dry-etch a polysilicon film 3 on an insulation film 2 such as SiO2, etc., obtained by heat-oxidizing on the surface of a silicon substrate 1 with reaction gas plasma, gas mixed optionally with any of hydric bromide gas, chlorine gas, and fluorine system gas being CF4, C2F6, NF3, CH2F2 is used as process gas. Thus, the polysilicon film 3 is reacted to chlorine gas to generate SiCl4, which is generated at comparatively higher reaction probability, so that etching speed of the polysilicon film 3 may become higher and further a generation of reaction products of SiO2 system generated on a resist pattern 4 with fluorine system gas may be restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor memory device such as DRAM, a very thin SiO ₂ film having a thickness of 100 Å or less
A method is used in which a film is used as a gate insulating film, a phosphorus-doped polysilicon film is deposited on the film, and this is dry-etched to form a gate electrode. In this case, the etching of the polysilicon film has a high selectivity to the SiO ₂ film in order to prevent damage to the very thin SiO ₂ film and the boundary layer with the silicon substrate (silicon substrate) below it. Is required. As a dry etching method satisfying such requirements, the spring 1992 lecture meeting of Applied Physics, P. 504 (Lecture N
o. 28p-NC-4), an etching method using a mixed gas of hydrogen bromide gas (HBr) and oxygen gas (O ₂ ) as a plasma gas is used.

When the polysilicon film is etched using hydrogen bromide gas (HBr) as a process gas as described above,
In order to prevent etching residues, it is usually 30 to 5 more from just etching (a state where predetermined etching is completed).
Perform 0% over-etching. For example, if the polysilicon film on the SiO ₂ film is removed by the etching for 60 seconds, the over-etching time is 18 seconds or more.
It takes about 30 seconds. However, this over-etching also etches the underlying SiO ₂ film, so that it is necessary to increase the etching selectivity of the polysilicon film with respect to the SiO ₂ film. In the above-mentioned lecture collection, high selectivity is obtained by adding oxygen gas (O ₂ ) to hydrogen bromide gas (HBr).

[0004]

However, in the dry etching using the above process gas, the problem that the etching rate of the polysilicon film is low, and a SiO ₂ -based reaction product is generated on the resist of the etching mask. Therefore, there is a problem that the resist cannot be removed by oxygen gas (O ₂ ) dry ashing without a wet treatment with a 0.5% HF solution.

Therefore, the present invention provides a method for manufacturing a semiconductor device, which can anisotropically and rapidly etch a polysilicon film when dry etching the polysilicon film, and which makes it extremely easy to remove a resist serving as a mask. With the goal.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention uses a hydrogen bromide gas, a chlorine gas, and a fluorine-based gas when dry etching a polysilicon film formed on an oxide film. A mixed gas obtained by mixing is used.

The fluorine-based gas is CF ₄ , C ₂
Consists of at least one of F ₆ , NF ₃ , CH ₂ F ₂ ,
The mixing ratio is preferably 1 to 5% with respect to the total flow rate of the mixed gas.

[0008]

In the present invention, by using chlorine gas as the process gas, the polysilicon film reacts with chlorine gas and SiCl ₄ is produced. This occurs with a higher reaction probability than SiBr ₄ due to bromine gas, and as a result, the etching rate of the polysilicon film is increased.
Further, by mixing a fluorine-based gas such as CF ₄ or the like, generation of SiO ₂ -based reaction products on the resist that is an etching mask can be suppressed, and as a result, resist removal after dry etching can be performed using oxygen gas (O 2). ₂ ) Only dry ashing is possible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 (a) to 1 (c) are views showing a manufacturing process of a polysilicon film to which the manufacturing method of the present invention is applied.

The manufacturing method of this embodiment will be described with reference to FIG.
As shown in (a), a semiconductor substrate 1 made of silicon or the like
Si obtained by thermally oxidizing the semiconductor substrate 1 on the surface
After the insulating film ₂ such as O ₂ is formed, a conductive film 3 made of polysilicon or the like is formed on the insulating film 2 by CVD (Chemical).
al Vapor Deposition; vapor phase growth)
Laminate by a method or the like. Further, a resist is spin-coated on the conductive film 3, and a desired resist pattern 4 is formed on the resist by photolithography.

Next, the resist pattern 4 is used as a mask to dry-etch the conductive film 3 by a parallel plate type plasma etching apparatus as shown in FIG. The plasma etching apparatus shown in FIG. 2 is disclosed in Japanese Patent Application No. 04-12962.
It is the same as the etching apparatus described in No. 3. This etching apparatus includes a chamber 6, an introduction pipe 7 for introducing a process gas into the chamber 6, a plate-shaped upper electrode 8a and a lower electrode 8b arranged in parallel, and electrodes 8a, 8
A high frequency power source 9 for applying a voltage between b and an exhaust pipe 10 for exhausting the process gas in the chamber 6 are provided.

The lower electrode 8b also serves as a wafer holder, and the wafer 5 is held above it. A cooling chamber 11 into which liquid nitrogen (may be water if necessary) is poured is provided below the lower electrode 8b.
Liquid nitrogen is used as a coolant, and the temperature of the wafer 5 is controlled by adjusting the flow rate with the solenoid valve 12. Further, the lower electrode 8b and the cooling chamber 11 are integrally rotatable by a motor or the like (not shown) at a high speed.

The introduction pipe 7 is provided with an MFC (mass flow controller) 13 for controlling the flow of process gas,
Further, the exhaust pipe 10 is connected to a vacuum pump 14. Then, the vacuum pump 14 reduces the pressure in the chamber 6 to maintain the vacuum state.

The etching conditions when using such an etching apparatus are, for example, HBr 50 sccm and Cl.
₂ 50sccm, CF ₄ 4sccm, processing pressure 0.4T
orr, RF power 250W. In this case, after performing a predetermined over-etching on the polysilicon film 3, as shown in FIG. 1B, generation of SiO ₂ -based reaction products on the resist pattern 4 can be suppressed, and as a result, as shown in FIG. As shown in FIG. 1 (c), normal oxygen gas (O
₂ ) The resist pattern 4 can be easily removed by dry ashing.

FIG. 3 shows a resist pattern 4 when the CF ₄ mixture ratio is changed as an etching process gas.
3 is a graph showing the film thickness of the above SiO ₂ -based reaction product and the etching selectivity between the polysilicon film that is the conductive film 3 and the SiO ₂ film that is the insulating film 2. The horizontal axis is the CF ₄ mixture ratio (%) with respect to the total flow rate of the process gas, and the vertical axis is the film thickness (Å / min) of the reaction product and the selection of etching of the polysilicon film and the SiO ₂ film Is a ratio.

According to the experiments conducted by the inventors of the present invention, when CF ₄ is mixed in the process gas used for etching, when the mixture ratio is 1% to 5%, SiO ₂ -based reaction formation on the resist pattern 4 is generated. Almost nothing happened.

This is the CF from CF ₄ mixed in a trace amount.
_{This is because the 3} radicals or F radicals suppress the generation of SiO ₂ -based reaction products that are intended to coat the resist pattern 4. However, by mixing CF ₄ with each other, the polysilicon film as the conductive film 3 and the Si film as the insulating film 2 are mixed.
Although the selectivity with respect to the O ₂ film may decrease, as shown in FIG. 3, even if the mixing ratio of CF ₄ is 5%, the etching selection ratio between the polysilicon film and the SiO ₂ film is 23. Yes, this has no practical problems.

In this embodiment, the parallel plate type plasma etching apparatus shown in FIG. 2 is used, but the present invention can be applied to an etching apparatus using electron cyclotron resonance (ECR) plasma.

Further, as the fluorine gas, C is used in the above embodiment.
Although F ₄ is used, C ₂ F is another gas to be added.
It is needless to say that the same effect can be obtained by using ₆ , NF ₃ , and CH ₂ F ₂ and that plural fluorine gases may be arbitrarily mixed.

[0020]

As described above, according to the present invention, in dry etching using reactive gas plasma, a mixture of hydrogen bromide, chlorine, and a fluorine-based gas is used as a process gas. This enables anisotropic and high-speed etching of the film, prevents the deposition of reaction products on the surface of the resist serving as an etching mask, and shortens the resist removing step.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps.

FIG. 2 is a schematic configuration diagram of a typical plasma etching apparatus used in the above embodiment.

FIG. 3 is a diagram showing etching characteristics of a polysilicon film formed by the method for manufacturing a semiconductor device according to the present invention.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Insulating Film 3 Conductive Film (Polysilicon Film) 4 Resist Pattern 5 Wafer 6 Chamber 7 Introduction Tube 8a Upper Electrode 8b Lower Electrode 9 High Frequency Power Supply 10 Exhaust Pipe 11 Cooling Chamber 12 Solenoid Valve 13 MFC 14 Vacuum Pump

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device, wherein a mixed gas of a hydrogen bromide gas, a chlorine gas, and a fluorine-based gas is used when dry-etching a polysilicon film formed on an oxide film. Method. 2. The fluorine-based gas is CF ₄ , C
_2. The manufacturing of a semiconductor device according to claim 1, comprising at least one of ₂ F ₆ , NF ₃ , and CH ₂ F ₂ , and having a mixing ratio of 1 to 5% with respect to the total flow rate of the mixed gas. Method.