JPS61220433A - Dry etching method - Google Patents

Abstract

PURPOSE:To regulate the dimension precisely, by implanting impurities into mask material before dry etching, and by producing the impurities near the mask at a high concentration during etching. CONSTITUTION:After W 2 is deposited on an Si substrate 3 and resist 1 is applied thereon, a pattern is formed. Next, S ions 5 are implanted into the resist by 10<13>-10<17> per cm<3>. Thereafter, if the W 2 is dry-etched with SF6, S 6 produced from the mask 1 sulfates the side walls of the W 2 to form a protective film 4 for preventing side face etching, with the result that an approximately vertical etching shape can be attained. According to the mask material, at least one of C, O, N, H, F and Cl may be implanted.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to dry etching methods, and more particularly to dry etching methods.

The present invention relates to impurity implantation into a mask material suitable for facilitating control of etching shape.

[Background of the invention]

The integration of LSIs is rapidly progressing, and it is necessary to improve the performance of dry etching, which is the main technology for microfabrication. In particular, highly accurate dimensional control is important for forming ultra-fine patterns, and various methods have been studied in the past. One such method is a method of mixing two or more types of gas as described in JP-A-53-124979. In this reference, anisotropic etching of AQ is performed using a mixture of hydrogen and a chlorine gas such as CCΩ or BCQ as an AQ dry etching gas.

The principle is as follows. In dry etching, ions and radicals in the plasma act as etchants that etch the material to be etched, but when ions are the main component of both, anisotropic etching is performed, and when radicals are the main component, wet etching is performed. This results in isotropic etching similar to . Therefore, in AM dry etching using chlorine gas, in order to achieve anisotropy, it is necessary to reduce chlorine radicals, and a method is to mix hydrogen into the etching gas by combining with chlorine radicals to form HCQ is valid.

However, in this method, since etching is performed mainly using ions in the plasma, there is a problem in that the etching selectivity is reduced due to the sputtering effect of the ions. Therefore, the above method of reducing radicals in plasma is not suitable for dry etching that requires a selectivity of several tens of times or more with respect to the underlying gate oxide film, such as dry etching of MOSLSI gate electrodes. .

On the other hand, in order to achieve anisotropic etching without significantly changing the amount of radicals, a method has been considered in which a protective film that is difficult to be etched by radicals is formed on the sidewalls of the pattern. To explain in more detail, for example, under etching conditions where deposits tend to adhere to the sample surface, if conditions are optimized such that the deposits are etched by ions but not by radicals, then the ion etching process can be achieved as shown in Figure 1. A protective film is formed only on the sidewalls of the pattern that are not irradiated, and side etching can be prevented. An example of an additive gas that forms such a deposit is a carbon compound such as CF or CCQ, which is usually present in an etching gas containing tens of volume percent or more.
Mix. Although the above method has higher selectivity than etching mainly using ions such as hydrogenation of Al etching, this method also reduces the partial pressure of the main etching gas by gas mixing, which reduces the amount of radicals and selects them. There is a tendency for sexual performance to decline.

It has been found that in any of the above etching shape control methods, it is extremely difficult to simultaneously control the etching shape and maintain high selectivity.

[Purpose of the invention]

In order to eliminate such conventional drawbacks, the present invention
To provide a dry etching method that achieves both high precision dimensional control and other improvements in etching performance, with the aim of controlling the gas composition of the plasma atmosphere only in the vicinity of an LSI pattern, which has a large effect on the etched shape. It is in.

[Summary of the invention]

Below, the experimental results that formed the basis of the present invention will be explained.

In this experiment, we investigated dry etching of tungsten, which has been used as a gate electrode in MOSLSI in recent years. SF was used as the main etching gas, and a selectivity ratio between tungsten and the underlying Sin was obtained at 30 or more, but since the side etch was relatively large at about 0.2 μm, an attempt was made to control the etching shape using a mixed gas. As a mixture, H
,, Nyu, 01. We tried various other gases and found that the shape could be improved with some mixed gases, but the effect was not seen unless the mixture exceeded several tens of volume percent, so in any case, the selection ratio (W /Sin, ) decreased significantly to 10 or less. Therefore, the above method is not suitable for practical use.

On the other hand, in dry etching of tungsten, it was found that the material of the mask has a significant effect on the etched shape. It has been found that when Sin is used as an etching mask, the side etch of tungsten becomes significantly larger than when a resist (AZ-1350J) is used. This is evidence that substances generated from the resist during etching have a large effect on the etched shape of the resist and the vicinity. By utilizing the influence of substances emitted from the resist and optimizing etching conditions such as gas pressure and electric power, the selection ratio (W/Sin, ) can be increased to 3.
It was confirmed that the side etch could be reduced to 0.1 μm or less while maintaining the value of 0 or more.

It is thought that the substance emitted from the resist has a very high concentration in the vicinity of several micrometers from the resist, and therefore it is presumed that it has a significant effect on the shape. In order to obtain the same effect as with resist using a mixed gas, a large amount of the mixed gas of 50% or more by volume must be added to the etching gas, and in this case, the main etching gas SF is no longer used.

The etching properties of the etch are significantly impaired and the etch rate is significantly reduced.

Selectivity and other properties cannot be maintained. Therefore, it is difficult to apply the above method.

Based on the above, the present invention utilizes the fact that impurities are injected into the mask material prior to etching, and that these impurities are generated at a very high concentration near the mask during etching and work effectively for shape control. death.

The purpose is to facilitate high-precision dimensional control.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

Example 1 As shown in FIG. 2, after depositing a 300n layer of tungsten (2) on a Si substrate (3), a resist (1) (AZ-1350) was deposited on the tungsten as an etching mask.
J) was applied. After that, a resist is formed into a desired pattern by a normal photo process.

Sulfur ions (5) were implanted into a 101-1017 co/d resist. Finally, the tungsten was dry etched using SF gas using the sulfur-injected resist as a mask. During etching, the side walls of the tungsten were sulfurized by sulfur (6) released from the etching mask, which acted as a protective film (4) to prevent side etching, resulting in a nearly vertical etched shape.

Example 2 When fluorine or chlorine ions are implanted into the resist instead of the sulfur ions shown in Example 1, the sidewalls of tungsten become a polymer film of carbon fluoride and carbon chloride, which are compounds of carbon and impurities in the resist. It was covered and the side etch was reduced.

Example 3 When carbon and hydrogen ions were implanted into the resist instead of the sulfur ions shown in Example 1, the amount of carbon and hydrogen increased compared to the original resist components, and the amount of hydrocarbons adhering to the tungsten sidewalls decreased. As the amount of the polymer film increased, the side etch prevention effect increased.

Example 4 Using Si instead of tungsten shown in Example 1,
When nitrogen ions were implanted instead of sulfur ions, the amount of nitrogen increased compared to the amount of nitrogen in the original resist component, and the side etch prevention effect of the nitride film on the Si sidewall increased.

Example 5 The etching mask of Example 1 may be made of a material other than resist. For example, almost the same side etch prevention effect was observed even when sulfur ions were implanted into a Sin mask.

Example 6 When oxygen ions were implanted into the Sin mask of Example 5, the amount of oxygen in the Sin increased, making it easier to form a tungsten oxide film on the tungsten sidewalls, reducing side etching.

Example 7 The ion implantation shown in Example 1 may be performed after resist application and before patterning, as shown in FIG. 3. In this case, due to changes in the composition ratio of resist components, the resist pattern resolution may be slightly reduced. Although some deterioration is observed, the effect of preventing side etch is maintained.

Example 8 Even if other impurity implantation methods are used instead of the ion implantation method shown in Example 1, the same effect can be obtained. For example, by soaking some H and O into the resist,
During etching, hydrogen and oxygen are generated from the mask material.

Since this oxygen oxidizes the tungsten sidewalls and forms a protective film, side etching can be reduced.

In addition, in the present invention, Mo other than W, W-8i, M
The same element can also be added to o-5i.

〔Effect of the invention〕

According to the present invention, it is possible to achieve anisotropic etching with high selectivity, which has been difficult in the past, and is therefore particularly effective for dry etching of gate electrodes. In addition, as is clear from the experiments that formed the basis of the present invention, the effect on the etching shape of the mask material is large; however, the present invention allows the influence of the mask material to be controlled to a certain extent, so it is possible to change the implanted impurity type for any mask material. This makes it easier to control the etching shape.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a pattern anisotropically etched with a sidewall protective film, and Fig. 2 is a schematic diagram of an impurity implantation method (a) into the mask material.
) and an explanatory diagram of how impurities generated from the mask material form a protective film on the sidewalls of the pattern during etching, resulting in anisotropic etching. An explanatory diagram of what to do. DESCRIPTION OF SYMBOLS 1...Mask material, 2...Etched material, 3...Substrate, 4...Pattern side wall protective film, 5...Impurity ions, 6...'$ 1 Figure 2

Claims (1)

[Claims] 1. When dry etching a substrate using an etching gas turned into plasma, an impurity is injected into an etching mask formed on the substrate prior to the dry etching. Dry etching method. 2. The dry etching method according to claim 1, wherein the impurity contains at least one of carbon, oxygen, nitrogen, hydrogen, fluorine, chlorine, and sulfur. 3. A dry etching method according to claim 1, characterized in that an ion implantation method is used as the impurity implantation method.