JPH0729878A - Dry etching method for copper thin film - Google Patents

Abstract

PURPOSE:To provide a dry etching technique wherein copper thin film patterns can be formed at such a low temperature as ordinary resin photoresists are applicable without using any toxic corrosive halogen gas. CONSTITUTION:A mixed gas containing at least oxygen together with gaseous hydrocarbon, such as methane, ethane and propane, is used for reactive gas. Highly volatile compound containing such linkage as COO-Cu and Cu-O, is formed in the areas uncovered with photoresist on the surface of a copper thin film using plasma energy. These compounds are transferred from the copper surface into vapor, and thus a copper thin film pattern is formed.

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 a copper thin film.

[0002]

2. Description of the Related Art As electronic parts are becoming smaller and highly integrated, finer circuit patterns are required, and the conventional pattern forming technology, wet etching, does not provide sufficient pattern finishing accuracy. There is a problem that the residue of the etching solution remaining on the substrate impairs reliability. In order to solve this problem, in semiconductor materials, insulating materials, and aluminum wiring, which is the main wiring material, etc., the materials are etched in a plasma of a gas that reacts with these materials to form a volatile compound, The dry etching for forming the pattern has been put to practical use.

On the other hand, the above-mentioned demand for miniaturization of the circuit wiring pattern means that a current having an excessive density is applied to the conventional aluminum thin film wiring, which causes problems such as breakage of the wiring due to electromigration. The use of a copper thin film as a wiring material is being studied.

In dry etching of this copper thin film,
For example, K. Ohno et al. (Cited by Ext. Abstr. 2
1st-Conf. , Solid State Dev
ices and Materials, Tokyo,
(1989), P157), a halogen-based gas such as silicon tetrachloride or carbon tetrachloride has been generally used as a reaction gas. However, since the vapor pressure of copper halide formed by the surface reaction of these gases and copper is low, the volatility is not sufficient, and etching proceeds unless the substrate on which the copper thin film is formed is heated to 200 ° C. or higher. do not do. Nevertheless, when etching a copper thin film to form an electric circuit, a pattern of a polymer resin photoresist is usually used as an etching mask. In the etching process, since the copper is etched after the etching mask is formed on the surface of the copper thin film, when the etching temperature reaches 200 ° C. or higher, the polymer resin as the etching mask deteriorates to improve the pattern accuracy. Not only is there a problem, but it is difficult to remove the etching mask after etching the copper thin film. Therefore, it is expected to develop a technique for etching a copper thin film at an etching temperature of 150 ° C. or lower, preferably 120 ° C. or lower.

[0005]

Therefore, in order to lower the etching temperature, JP-A-3-295232 and JP-B-61-40757 have been proposed. In the former method, the copper-based thin film is etched using an etching gas containing nitrogen and oxygen, but the etching temperature is still high at 150 ° C. to 200 ° C., and the etching mask is 200 ° C. Since it is required to have heat resistance to some extent, it cannot be satisfied.

On the other hand, the latter method, which drastically lowers the etching temperature, forms a methyl group or a methylene group during glow discharge, and this forms a volatile compound with copper directly or in an intermediate step. Since it is used for etching, most halogen-based gases such as methyl chloride and methyl iodide are used as reaction gases. However, halogen gas is highly toxic and corrosive, and its consumption has become a social problem. Therefore, when using these gases, there is a problem in that considerable facility measures such as measures against leakage and appropriate measures for exhaust gas are required.

Therefore, an object of the present invention is to provide a method capable of dry-etching a copper thin film at a temperature of 120 ° C. or lower without using a halogen-based gas having a problem of toxicity or corrosiveness. It is a thing.

[0008]

Means for Solving the Problems As a result of intensive studies, the inventors of the present invention simply used gaseous hydrocarbons when etching a copper thin film on a substrate with a predetermined masking under high frequency discharge. It was also found that although the phenomenon of deposition on the copper surface occurs, etching does not proceed, but when oxygen coexists, the deposition of hydrocarbons stops and etching starts on the copper surface. The present invention has been carried out based on such findings, and is characterized in that a mixed gas formed by coexisting at least oxygen gas with gaseous hydrocarbon is used as a reaction gas. The gaseous hydrocarbon which constitutes the main component of the reaction gas is preferably composed of methane, ethane, propane or a mixed gas thereof which is a gas at room temperature.

[0009]

[Effects of the Invention and Effect of the Invention] It is not clear how the etching effect of hydrocarbons in the presence of oxygen develops, but the infrared of the deposit on the glass substrate installed on the inner wall of the reactor away from the discharge region It can be inferred from the spectroscopic analysis as follows. FIG. 1 shows the results when the copper thin film sample was not installed and the results. As is clear from this figure, when the copper thin film is etched under the conditions of the present invention, absorption that suggests a bond between COO-Cu and Cu-O is characteristically recognized. This is because methane and oxygen form a compound containing these bonds on the copper surface,
This indicates that this was volatilized and transferred from the copper surface and deposited on the glass substrate on the inner wall of the reactor. Therefore, oxygen not only forms a compound that is easily volatilized by combining with a hydrocarbon, but also has a high affinity with copper. Therefore, in a plasma in which hydrocarbon and oxygen coexist, copper is carbonized through oxygen. It is believed that it combines with the hydrogen component to form a highly volatile compound, which is easily removed from the copper surface to enable etching. On the other hand, in the case of copper, for example, methyl copper, which is described in a chemical dictionary (Morikita Publishing, (1981), P1262), exists as a solid at a low temperature, but -20 ° C during the temperature rising process.
As a result, it decomposes into copper, methane and ethane. This is
It means that alkyl copper is not formed under general temperature conditions, and even if it is formed, it is poor in volatility.
Furthermore, since the bond between copper and carbon is unstable, it is considered difficult for copper to directly bond with methane or the like to form a compound, and the existence of such a compound is not recognized.

Therefore, according to the present invention in which hydrocarbon and oxygen are used as reaction gases, it is possible to use a general resin-based photoresist as an etching mask without using a halogen-based gas having a problem of toxicity and corrosiveness. It enables dry etching of copper thin film.

In the present invention, as described above, a compound containing a bond such as COO-Cu or Cu-O is detected as a volatile substance from the copper surface, and therefore a chemical reaction on the copper surface advances etching. I think. However, considering the temperature / power / pressure dependence of the etching rate, which will be described below, the contribution of the physical sputtering phenomenon due to ions cannot be ignored. On the other hand, the finish of the etched surface becomes rough only by a physical phenomenon. Incidentally, when the etching by the discharge of only argon was attempted, the etching of the copper thin film was possible. However, when the fine shape of the surface to be etched was examined in detail, as shown in FIG. It can be seen that the etching surface having only a physical phenomenon such as sputtering is very rough as compared with the case of the method according to. That is, in the etching mechanism of the present invention, it is not enough to perform a physical etching action, and it is necessary to allow oxygen to coexist in the gaseous hydrocarbon in order to cause a chemical reaction on the copper surface. A gas that performs a physical etching action, such as, may coexist. Incidentally, the oxygen concentration in the reaction gas is not particularly limited, it is possible to etch the copper thin film in a wide oxygen concentration range, when the oxygen concentration is low, a polymer is deposited on the etched surface, Moreover, when the concentration is high, an oxide of copper is formed, so that it is necessary to select an appropriate concentration.

[0012]

EXAMPLES The reactor used for the experiment was a commercially available reactive ion etching (hereinafter referred to as RIE) apparatus, and the sample to be etched was formed into a film on a slide glass substrate by a vacuum deposition method or a sputtering method. A copper thin film was used. A commercially available resin photoresist was used for this copper thin film, and after forming an etching mask for the wiring pattern, it was subjected to an etching experiment. Further, methane used as an etching gas is a commercial product filled in a cylinder as pure methane, and oxygen is a commercial commercial product.

A copper thin film sample was placed on the cathode electrode of this reactor, and a clean glass substrate was placed on the inner wall of the reactor away from the discharge area.
After preliminarily evacuating the inside of the reaction vessel using a booster pump, it was evacuated using an oil diffusion pump until the pressure became 1 × 10 ⁻⁵ Torr or less. After that, change the flow rate of methane gas to 26
SCCM and oxygen flow rate was set to 4 SCCM and introduced into the reaction vessel, and the valve on the exhaust side was adjusted so that the pressure became 50 m · Torr (the oxygen concentration at this time was 10%). Although only methane and oxygen were used as the gas introduced into the reactor here, an inert gas such as argon may be added as the carrier gas.

Thereafter, the power density is 1 W / c between the cathode electrode and the anode electrode provided opposite thereto.
A high frequency power of m ² was applied to cause discharge, and the mixture was left as it was for 3 minutes. At this time, since the substrate was not heated, the substrate temperature at the start of discharge was room temperature, but it increased to 110 ° C. due to the energy of discharge after 3 minutes. Since the RIE device does not have a substrate heating mechanism, the temperature of the sample changes depending on the applied high frequency power and time. For example, given the power density shown here,
Although the temperature rises rapidly with the start of discharge, it stabilizes at 170 ° C. in about 20 minutes.

When the sample subjected to the above-mentioned treatment was taken out from the reactor and observed, the copper surface of the portion to be etched exhibited a vivid metallic luster, and infrared spectroscopy (IR) and X-ray photoelectron analysis (XPS) were used. ), No polymer deposition or copper oxidation was observed at all.

Next, the etching mask previously formed on the copper surface of the sample was removed with a solvent, and the dimension of the step formed at the boundary with the surface to be etched was measured. As a result, the etched portion had a recess of about 30 nm. Occurs and the substrate temperature is 1
It was found that the etching proceeds at a rate of about 10 nm / min under the condition of 10 ° C. or less.

In order to examine the relationship between the etching rate and the substrate temperature, the etching depth was examined for samples having different etching times. The experiment in which the etching time was changed in order to observe the influence of the substrate temperature is based on the property that the temperature rises with the time described above. As a result, when the substrate temperature is 110 ° C, the etching rate hardly changes up to 150 ° C.
Although it increased by about 20% at 70 ° C, no significant influence of temperature on general chemical reaction was observed.

Further, in order to investigate this phenomenon in detail, an experiment was conducted by changing the high frequency power and the pressure during etching. As a result, when the electric power was small, the etching rate increased with the increase of the electric power, but it hardly changed at the electric power of 1 W / cm ² or more. As for the pressure dependence of the etching rate, the etching rate decreased with increasing pressure.

Further, in this experiment, the initial pressure of the reactor was remarkably lowered, and then methane and oxygen were introduced as reaction gases. However, when the pressure is reduced only by a simple device such as a rotary pump, the initial pressure is about 10 m · Torr, and most of the residual gas components are water molecules composed of H—O. As is well known, this water component is dissociated by discharge to generate oxygen. Also, considering that the pressure of dry etching is generally several tens of m · Torr, when such a simple apparatus is used, even if only methane is used without introducing oxygen, the high concentration existing as a residual gas is high. The present invention can be realized in combination with the oxygen.

As described above, when methane is used as the hydrocarbon and the copper thin film is etched by the reactive gas to which oxygen is added, the copper surface is reacted with methane and oxygen to form a highly volatile copper compound. I knew it would be done. Then, in order to investigate whether this phenomenon is common to hydrocarbon gases, methane was changed to ethane or propane, and etching of a copper thin film was also tried.

A commercially available pure ethane filled in a cylinder was used as ethane, and the experiment was conducted under the same conditions as for methane. As a result, the copper thin film was etched by adding oxygen, and the etching rate at this time was For example, the oxygen concentration is 3
It was 6.5 nm / min at 1%.

Next, as a result of the same experiment using commercially available propane, the copper thin film is also etched in this case by the mixed gas with oxygen. For example, when the oxygen concentration is 43%, the etching rate is 3.5 nm / It was a minute.

In the above results, it was possible to etch the copper thin film by adding oxygen to both methane, ethane and propane. Therefore, the gas consisting of these hydrocarbons is not limited but is a mixed gas thereof. However, it is clear that etching can be performed by adding oxygen.

With respect to the results of the present invention shown above, these prior arts were confirmed by experiments for the purpose of clarifying the difference from the previously disclosed JP-A-3-295232 and JP-B-61-40757. However, JP-A-3
In the method of -295232, an oxide film on the surface of the copper thin film was formed, and in the method of JP-B-61-40757, copper halide was formed and etching could not be performed.

[Brief description of drawings]

FIG. 1 is an absorption spectrum diagram of infrared spectroscopic analysis showing the results of analysis of a reaction product volatilized from the surface of copper according to the present invention and a reaction product in the absence of a copper thin film sample.

FIG. 2 is a diagram showing a difference in roughness between the present invention and a copper surface etched by sputtering with argon ions.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/3205 21/3213 8826-4M H01L 21/88 D

Claims (2)

[Claims] 1. When carrying out reactive ion etching of a copper thin film on a substrate on which a predetermined masking is applied under high frequency discharge, a mixed gas in which at least oxygen gas is made to coexist with gaseous hydrocarbon is used as a reaction gas. Characteristic dry etching method for copper thin film. 2. The dry etching method according to claim 1, wherein the gaseous hydrocarbon which constitutes a main component of the reaction gas is methane, ethane, propane or a mixed gas thereof which is a gas at room temperature.