JPS61256725A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable the process according to the mask size by introducing ammonium gas into a vacuum chamber alternately with a halogen gas when the gas including a halogen element is introduced in the vacuum chamber to produce a plasma and the etched material is subjected to dry etching therein. CONSTITUTION:In the vacuum chamber 6 comprising a discharge tube 4 projecting to the upper side and having electromagnets 5 arranged on its periphery, a sample table 11 provided with a permanent magnet 12 arranged on the lower side is arranged. On that table, the sample to be etched 10 which is easy to produce side etching such as W, Mo, and Ti is placed. Next, a halogen gas such as SF6 is introduced into the vacuum chamber 6 from a gas source 9 through a pipe 7 and at the same time, a microwave from a microwave oscillator 1 connected to a power source 2 is made incident into the discharge tube 4 through a waveguide 3. At that time, NH3 gas is also contained in the gas source 9 nd these gasses are introduced alternately while a flow control valve 8 controlled by a controller 13 is actuated to prolong the time for the NH3 gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a dry etching method in an LSI manufacturing process, and particularly to an etching gas introduction method suitable for forming fine patterns with high precision.

[Background of the invention]

Traditional methods for improving dimensional accuracy in dry etching include solid state technology (Sol).
id 5tate Technology) 1984
There is a method of introducing two or more gases into a vacuum chamber at the same time, as shown in April 2013, pages 235-242. In this case, W
SF, +C2C1'' is a two-layer gate of silicide and polysilicon (also called polycide gate).

Dry etching is performed in a plasma of a mixture of two types of gases (Freon 115) to control the etching shape, particularly to suppress side etching. Both W silicide and polysilicon are SF.

Etching can be performed in a single gas plasma, but in this case there is a drawback that the amount of side etching becomes very large. Therefore, in the cited example, C and CMF are used as a mixed gas to suppress side etching, and SF and C2C are used as a mixed gas to suppress side etching.
By optimizing the mixing ratio of l2F, the amount of side etching of W silicide and polysilicon is reduced.

In the dry etching of the W gate, SF gas can also be used as the main etching gas. In this case, the disadvantage is that the amount of side etching is as large as 0.2 to 0.3 .mu.m on one side, similar to the etching of polycide. The authors used S as a mixed gas to suppress side etching of W, including C2CΩF.
A method of adding F. was investigated, but unlike the case of polycide in the cited reference, no side etch suppressing effect was observed.

[Purpose of the invention]

The purpose of the present invention is to greatly reduce the amount of side etching in the dry etching of W, Mo, Ti and their silicides, which cause side etching as described above, and to achieve high accuracy according to the mask dimensions. The object of the present invention is to provide an etching method that can accomplish the processing.

[Summary of the invention]

One possible method for suppressing side etching of W is to form a substance that is difficult to be etched on the side walls of W. W oxides and nitrides are materials that can be formed on the W sidewalls and are difficult to etch.

Alternatively, a carbon compound-based polymer film may be considered, but it has been found that among these, W nitride can be efficiently formed in ammonia gas plasma. On the other hand, nitriding of W in nitrogen plasma was also considered, but nitrides could hardly be formed.

Based on the above experimental results, during W etching,
The idea was to suppress etching in the lateral direction under the mask while forming W nitride on the W sidewalls using ammonia gas plasma, thereby achieving etching with less side etching. To actually do this, SF and ammonia are alternately introduced into the vacuum chamber, and while the SF plasma is being generated, the etching of W is progressing, and while the ammonia D plasma is being generated, the W sidewall is being etched. In ammonia plasma, W
Both the sidewalls and the flat surface are nitrided, but the nitride film formed on the rough surface is removed by the next cycle of SF and ion irradiation in plasma. On the other hand, since there is almost no ion irradiation on the W sidewall, the W nitride film is difficult to remove.

In addition, SFG and ammonia were introduced into the vacuum chamber at the same time,
Although W was etched in these mixed gas plasmas, it was difficult to form a W nitride film, and there was almost no effect of suppressing side etching of W.

[Embodiments of the invention]

Hereinafter, one aspect of the present invention will be explained in detail.

[Example 1] FIG. 1 shows an example of the configuration of a plasma etching apparatus using the present invention. The plasma generating means is magnetic field microwave discharge, and the material to be etched is W. Gas source 9 is SF
, and ammonia. The gas flow rate is adjusted by a gas flow rate adjustment valve 8, and a controller 13 allows SF and ammonia to be supplied intermittently.

FIG. 2 shows the time for flowing SFG and ammonia, and the amount of change in the gas flow rate. SF.

The gas flow rates of ammonia and ammonia were each set to I.times.10@-3 Torr as a partial pressure in the vacuum chamber 6. The times for introducing SF and ammonia into the vacuum chamber were 5 sec and 20 sec, respectively, within one cycle of 25 sec.

FIG. 3(a) is a diagram schematically showing a cross section of a W gate when etched under the conditions shown in FIG. , the mask was etched according to the dimensions.

Figure 3(b) shows the introduction of SF and ammonia into the vacuum chamber for 1 time at the same gas flow rate as shown in Figure 2.
20 sec and 5 s in a period of 25 sec, respectively.
FIG. 3 is a sectional view of the W gate after etching in the case of ec. In this case, no significant side etch suppression effect is observed.

[Example 2] Even when the conditions shown in FIG. 2 in Example 1 were changed as shown in FIG. 4, side etching of W could be reduced.

However, the niche velocity of W decreased by about 30-40%.

[Example 3] Even when a normal reactive sputtering device as shown in FIG. 5 is used in place of the microwave plasma etching device shown in FIG. 1 in Example 1, side etching of W can be suppressed. The effect was recognized. However, since the dissociation efficiency of ammonia gas is lower than that of microwave plasma etching equipment, W
The efficiency of nitriding also decreased, and side etching increased slightly compared to Example 1.

[Example 4 Instead of W shown in Example 1, Ti and Ta were used.

A similar side etch suppression effect was observed when Si or a Si compound of W, Ti, or Ta was used as the material to be etched. However, since the nitriding efficiency of each material differs, it was necessary to slightly change the gas flow rates of SF and ammonia for each material.

[Example 5] Instead of SF g shown in Example 1, SF.

A similar side etch suppression effect was also observed when a gas containing fluorine such as NF was used.

[Example 6] In Si etching, CCQ and ammonia were alternately introduced into the vacuum chamber as in Example 1. In this case as well, Si nitride was formed on the Si@ wall, and the effect of suppressing side etch was observed.

〔Effect of the invention〕

According to the present invention, W, Ti, and T
Since highly accurate etching of a, Si, or their compounds can be performed, it is possible to form ultra-fine wiring patterns in the range of 0.8 μm to 0.5 μm.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the microwave plasma etching apparatus used in the present invention, and FIG. 2 is a diagram illustrating the time interval for alternately flowing SF and ammonia, and the set value of the gas flow rate.
Figure 3(a) is a schematic diagram of the cross section of the W gate when etched under the conditions left in Figure 2, and Figure 3(b) is a schematic diagram of the W gate cross section when etching is performed under the conditions remaining in Figure 2. FIG. 4 is an explanatory diagram of a case where ammonia is continuously supplied, and FIG. 5 is a schematic diagram of a reactive sputtering apparatus that can be used in the present invention. DESCRIPTION OF SYMBOLS 1... Microwave oscillator, 2... Power supply for microwave oscillator, 3... Waveguide, 4... Discharge tube, 5... Electromagnet, 6... Vacuum chamber, 7... Piping, 8...Gas flow rate adjustment valve, 9...Cylinder, 1o...Sample, 11...
- Sample stage, 12... Permanent magnet, 13... Controller, 14... Etching mask, 15... Tungsten (W), 16... Silicon oxide film, 17... Lower electrode, 18... ... Upper electrode, 19... Blocking capacitor, 2o... High frequency power supply, 21... W nitride film. f 1 Illustrated iris 2 Illustrated f! leaf area

Claims (1)

[Claims] 1. In a method of introducing a gas containing at least a halogen element into a vacuum chamber to generate gas plasma and dry etching a material to be etched in the plasma, the gas containing the halogen element and ammonia are mixed during etching. A dry etching method characterized in that the material to be etched is alternately exposed to a gas plasma containing a halogen element and an ammonia gas plasma, by alternately introducing a gas into a vacuum chamber. 2. The time for introducing the halogen element-containing gas and ammonia gas according to claim 1 into the vacuum chamber is:
A dry etching method that is at least periodic and is characterized in that the time for introducing ammonia in one cycle is longer than the time for introducing a gas containing a halogen element.