JP2834129B2 - Low temperature dry etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a low-temperature dry etching method, and in particular, a sample temperature range in which anisotropic etching can be achieved can be made higher than when only SF ₆ is used, and etching controllability can be improved. And how it can be improved.

[Conventional technology]

Conventional silicon etching is disclosed in Japanese Patent Application Laid-Open No. 61-8926 or Journal of Vacuum Science and Technology.
chnology) B5 (2) As described in Mar / Apr1987 P594,
Deposition gases such as CF ₄ and CBrF ₃ are mainly used. A film is formed on the side surface of the etching in these gas plasmas, and anisotropic etching is performed by utilizing the fact that side etching is prevented. In some cases, in addition to the above gases, an additive gas for more positively depositing a film is added.

[Problems to be solved by the invention]

In the above prior art, it has been clarified that a film of a carbon-based compound, silicon oxide, an aluminum-based compound, or the like adheres to the etching side surface. Since these adhered films remain after dry etching, there is a problem that post-treatment for removing the films is required. In addition, depending on the type or amount of the adhered film, it may be difficult to remove the film by post-processing, and this has caused foreign matter and contamination in the post-process.

The same etching method is widely used for dry etching other than Si, and a typical example is etching of aluminum with CCl ₄ gas. In any case, there is a considerable problem of contamination and the like, and it is preferable not to use a gas for forming this kind of film. However, according to the prior art, anisotropic etching with this kind of non-depositing gas is difficult. It was difficult.

An object of the present invention is to achieve anisotropic etching by a method in which an adhered film does not remain on an etching side surface after etching.

[Means for solving the problem]

The above object is achieved by performing low-temperature dry etching while forming a material which adheres to the etching side surface at low temperature and becomes volatile at room temperature as a side wall protective film. That is, a material whose vapor pressure at the time of low-temperature dry etching is lower than the pressure in the vacuum processing chamber and whose vapor pressure at room temperature is higher than the pressure in the vacuum processing chamber is used as the side wall protective film. As a specific example, SiCl ₄ or the like can be applied. As can be seen from the vapor pressure graph of FIG. 2, for example, SiCl ₄ is in a normal etching gas pressure range of 0.1 T
At orr, adsorption begins at about 1100 ° C. Therefore,
When the sample temperature is set to -100 ° C or lower, this adsorption layer functions as a side-etching prevention film covering the etching side surface. If the pressure in the vacuum processing chamber is, for example, 0.2 Torr during the process of elevating the sample after etching, SiCl ₄ evaporates at about −100 ° C., so that no film remains as a contamination source.

[Action]

The operation of the present invention will be described in detail by taking Si etching as an example. When etching Si using fluorine-based gas,
The active particles of fluorine react with Si to form SiF ₄ and evaporate. Since the vapor pressure of SiF ₄ is sufficiently high at room temperature as shown in FIG. 2, etching can be performed at a very high speed at room temperature. On the other hand, the side surface of the etching is also easily reacted, so that side etching occurs. When the sample is cooled to a low temperature, the vapor pressure of SiF ₄ gradually decreases, and the reaction on the etching side is suppressed to enable anisotropic etching, but the optimum temperature is -120 to -1.
Very low at 50 ° C.

When a chlorine-based gas is mixed with the above-mentioned fluorine-based gas, SiCl ₄ is generated in addition to SiF ₄ . Since SiCl ₄ evaporates at a temperature higher by 50 to 80 ° C. than SiF ₄ , under the above etching conditions, SiCl ₄ is adsorbed on the Si surface and acts as a protective film for preventing side etching as shown in FIG. Accordingly, the anisotropic etching is achieved by setting the conditions shown by the oblique lines in FIG. This optimum temperature range is 50 to 80 ° C. higher than when only the above-mentioned fluorine-based gas is used,
The reliability was improved in the control of the sample temperature and the structure of the device. Note that the above-mentioned fluorine-based gas and chlorine-based gas must be non-sedimentary gases from the viewpoint of preventing pollution, but the above-mentioned effects can be achieved by using a sedimentary gas.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

[Example] An Si wafer was placed on a cooling sample stage provided in a vacuum processing chamber, and the wafer was cooled to -100 ° C using liquid nitrogen. A vacuum processing chamber with SF ₆ gas Cl ₂ gas 8: was introduced at a rate of 2, and discharging at a high frequency of 13.56MH _Z. Gas pressure about 0.
The gas flow rate was 15 Torr and the gas flow rate was about 20 cc / min. At this time, the Si wafer was etched at a speed of about 1 μm / min, and anisotropic etching in which almost no side etching was detected (0.03 μm) was achieved. After the etching was completed, the Si wafer was transferred to a vacuum preparatory chamber separate from the processing chamber, where the temperature was raised to room temperature (about 20 ° C.) by a heater, and then transferred to the atmosphere. Thereafter, the resist assuring step using oxygen plasma was completed. As a result of observing the Si wafer after assuring, it was found that there was no foreign matter or contamination that would hinder the subsequent process, and that no post-treatment was required to prevent the contamination.

The above-mentioned etching conditions can be changed, and the sample temperature range in which anisotropic etching can be obtained is changed to -50 to -120 ° C depending on setting conditions such as gas pressure, gas flow rate, and input power.

The above processing gas may be of another type, and it is recognized that almost the same effect can be obtained by using NF ₃ , BF ₃ , F ₂ as a fluorine-based gas and SiCl ₄ , BCl ₃ as a chlorine-based gas. Was done.

〔The invention's effect〕

According to the present invention, a substance that evaporates at room temperature after etching is used as a side wall protective film, so that there is an effect that a clean dry etching process free from contamination and foreign matter can be realized. In addition, the etching speed is high, and anisotropic etching can be easily achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the effect of the present invention, and FIG. 2 is a graph showing the relationship between the vapor pressure of SiCl ₄ and the temperature. 1 Etching mask, 2 Etching side (for example, Si), 3 Etching bottom, 4 Reaction product (for example, SiF ₄ ), 5.
l ₄ ), 6 ... Ion.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-158627 (JP, A) JP-A-62-292324 (JP, A) JP-A-61-187238 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 21/3065

Claims (2)

(57) [Claims] A first step of cooling silicon in the processing chamber to a first temperature higher than -120 ° C., introducing a fluorine-based etching gas and a chlorine-based additive gas into the processing chamber; Reacting a gas with the silicon to form a sidewall protection film on the side surface of the silicon, and etching the silicon with the etching gas; elevating the temperature from the first temperature to room temperature to volatilize the sidewall protection film; And dry etching the silicon. 2. The dry etching method according to claim 1, wherein said first temperature is -50 ° C. or lower.