JPS60186411A - Method of dry etching - Google Patents

Abstract

PURPOSE:To carry out anisotropic etching to cause no undercut at all, by subjecting a polycrystalline silicon film on a wafer substrate heated at a proper temperature to dry etching by the use of a mixed gas of CCl2F2 and N2 as a reaction gas. CONSTITUTION:The polycrystalline silicon film 201 formed on the silicon oxide film 203 grown on the silicon wafer substrate 202 has the mask 204 of photoresist or other etching-resistant film, the wafer substrate 202 is heated to 30- 100 deg.C, and dry etching is carried out by the use of a mixed gas of CCl2F2 and N2 as a reaction gas. Consequently, improved anisotropic etching having no undercut at the interface 205 between the polycrystalline silicon film 201 and the oxide film 203 can be carried out while keeping high selectivity for the oxide film 203 of the substrate and the mask 204. A flow rate of N2 gas in the total flow rate of the mixed gas is preferably 5-80wt%, and etching pressure is preferably 4-50Pa.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dry etching a polycrystalline silicon film.

In the manufacture of silicon semiconductor integrated circuits, particularly in MO8 type integrated circuits, polycrystalline silicon films are often used as gate electrode materials, and etching of polycrystalline silicon films has become a very important technique.

As an etching method for this polycrystalline silicon film, conventional CF
, although processes using reactive gases mainly composed of gases are commonly used.

This method has the disadvantage of creating a large undercut under the photoresist mask material, making it unsuitable as an etching method for polycrystalline silicon films when forming ultra-LSI patterns that require finer patterns. there were.

As a method to solve this problem, reactive ion etching technology using a gas system containing chlorine atoms has been adopted, and this has made it possible to obtain so-called anisotropic etching characteristics. There are disadvantages in terms of dimensional accuracy and selectivity to the oxidation pattern of the base.1For example,
In etching using a gas system containing eel as the main component,
The selectivity to the photoresist was low, and there were drawbacks such as leaving a residue on the underlying oxide pattern.

Yet again. CF3Br-? Etching using CCl3F was satisfactory in terms of undercutting, but had the disadvantage that a large amount of residue remained on the base after etching.

Yet again. Etching with a gas system containing CI gas as the main component can cause problems if the amount of CI gas is not sufficiently controlled.
Large undercuts may occur, and the photoresist may also be deformed after etching.

In order to solve this problem, the inventor of the present application has arrived at a new etching method as described below. This will be explained in detail below.

First, etching with CCI, F, gas is performed on photoresist.

High selectivity to the underlying oxide film and fast etching speed.

It has been found that it exhibits superior etching properties compared to other gas systems. However, with this gas etching,
When etching is complete and the underlying oxide film is exposed, 9
It was soon observed that a peculiar large undercut was produced near the interface between polycrystalline silicon and the underlying oxide film, and the etching gas for polycrystalline silicon films in VLSIs that adopted the rules of 2 to II#. As it turned out to be very difficult to use.

However, as the research continued, it became clear that when etching was performed using a gas system in which N2 gas was mixed with CCI□F2 gas, high selectivity was maintained with respect to the underlying film and photoresist mask. While.

Furthermore, it has been discovered that good anisotropic etching can be performed without causing any of the above-mentioned peculiar undercuts that occur when only CCl2F2 gas is used.

Figure 1 of the case shows a cross-sectional view of a polycrystalline silicon film subjected to reactive ion etching using only id and CCl2F2 gas. The polycrystalline silicon film 101 shown in the figure has a thickness grown on a silicon substrate 102.

The photoresist 104 is deposited on a silicon oxide film substrate of several hundred amps (angstroms).
Cover with a mask.

This figure shows a cross section after reactive ion etching.

At the interface between the polycrystalline silicon film 101 and the silicon oxide film J03.

A large undercut 105 has occurred. It has been observed that the speed at which the undercut 105 advances depends on the flow rate of CCl2F2 gas, and the amount of undercut decreases when the flow rate is small. and.

It has been found that this unique undercut 105 cannot be prevented by etching using only CCI and F2.

FIG. 2 is a cross-sectional view when a polycrystalline silicon film is etched using a gas system in which N2 gas is mixed with CC1zR gas. The figure shows a cross section of a polycrystalline silicon film 201 on an oxide film 203 grown on a silicon wafer 202, which was subjected to reactive ion etching using the first resist 204 as a mask. With this gas system, it is possible to perform anisotropic etching without causing any undercut at the interface 205 between the polycrystalline silicon 201 and the silicon oxide film 203.

However, in this gas system, in order to perform optimal etching while maintaining the anisotropic etching characteristics of polycrystalline silicon, it is necessary to set the gas flow rate, etching pressure, high frequency power, etc. quite strictly. be. For example, if the amount of N2 gas mixed is small, CCI.

Undercuts similar to those obtained with F2 alone are seen, and a high N2 gas flow rate slows down the etching rate of polycrystalline silicon. The mixed amount of N2 gas is
It has been found that it is desirable to set the flow rate ratio of the total flow rate of CCl2F2 gas and N2 gas in a range of 5% or more and 80% or less.

In this case, if the etching pressure is too low by -1, the selectivity to the photoresist will decrease and the pattern transfer accuracy will deteriorate. It was also found that it is desirable to set

According to the experiments of the inventors - for example, CCl2F,
Flow rate 4QSCC [NZ flow i12SCCM, etching pressure 15Pa, etching power density 0.17W/
i r 13.56 M) TE ), the etching rate of phosphorus-doped polycrystalline silicon is 2,000 M'' or more, and the selectivity to silicon oxide film is 20 or more.
The value for photoresist was also 10 or more. The transfer accuracy of the etching pattern is determined by transferring it to the polycrystalline silicon pattern with a difference in width of the resist mask pattern within ''io, iμm, and even if over-etching is performed for a long time, the pattern width remains It was found that the present invention did not shrink, and it was confirmed that the present invention can be sufficiently applied to a 5LSI manufacturing process that requires microfabrication, especially as a batch-type mass production process.

The inventor of the present application further conducted research and discovered that when dry etching a polysilicon film using a gas system containing CCl2F2 gas mixed with N2 gas, the electrode stage on which the wafer was placed was
When heating the polycrystalline silicon film to 100°C to 100°C, the polycrystalline silicon film is heated to the underlying oxide film and photoresist mask without leaving any residue while maintaining the above-mentioned large selectivity.
In addition, we have found that anisotropic etching can be performed at a faster etching rate than when the electrode is conventionally cooled by water cooling at room temperature of around 20°C.When the etching pressure is 16 Pa, the temperature of the electrode circulating water is is 2
At 5°C (10m/T = 3.36K), the etching rate of phosphorus-doped polycrystalline silicon is approximately 2.20 OA/
”, but the temperature of the circulating water was increased to 80℃ (10”/T).
= 2.83K), which is about 260O
The selectivity for the photoresist decreased somewhat, but the selectivity for the oxide film did not change.

6-Also, when the etching pressure is 19 Pa, the electrode circulating water temperature is usually 20°C to 30°C (103/T=3.41K to
When the temperature was >3.30K, a lot of residue was generated and it could not be put to practical use, but when heated in a 70℃ trench, there was no residue and the temperature was about 3.3K. Etching rates of Q n OA/m were obtained.

The present invention is as described above, and as a reactive gas.

CCN2Ii2TN, +7) Using a mixed gas, dry etching is carried out with the substrate heated to 30°C to 100°C. When etching polycrystalline silicon films with the method according to the invention, there is no residue.

Anisotropic etching with high selectivity and high etching speed is possible.

The present invention greatly contributes to the manufacturing of VLSIs.
It can be said that it is an industrially significant invention.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a pattern obtained when a phosphorous-doped polycrystalline silicon film is etched using only CCl2F2 gas. FIG. 2 is a cross-sectional view of a pattern when the same phosphorus-doped polycrystalline silicon film is etched by mixing CCρ2F2 gas with N2 gas. FIG. 3 is a graph showing the change in the etching rate of polycrystalline silicon with respect to the temperature of the electrode circulating water. ](N, 201...Polycrystalline silicon film 102
．． 202...--Substrate wafer 103.
203...Silicon oxide film 104, 204...
. . Photoresist mask 105 . . . Unique undercut 205 that occurs at the interface between the polycrystalline silicon film and the oxide film 205 . . . The interface between the polycrystalline silicon film and the oxide film. Patent applicant Nichiden Anelva Co., Ltd.

Claims (2)

[Claims] (1) In a dry etching method in which a polycrystalline silicon film is etched using a photoresist or other etching-resistant film as a mask, the wafer substrate is heated to
CCI as a reactive gas heated to a temperature of 00 °C,
F! A dry etching method characterized by using a mixed gas of and N. (2) The dry etching method according to claim 1, characterized in that the flow rate of the N gas is 5% to 80% relative to the total flow rate of CCI, F2, and the like. (31 CCt) The dry etching method according to claim 1 or 2, characterized in that the etching pressure of the mixed gas of F'2 and N2 is *4 Pa to 50 Pa.