JPH01201493A - Porous conductive material and production thereof - Google Patents

Abstract

PURPOSE:To produce a porous conductive material which uniformly contains Si and has good corrosion resistance by forming SiC particles coated with an org. material on the surface and subjecting the particles to an org. material carbonization treatment to form the molding of a specific bulk density, then bringing the same into contact with the molten Si. CONSTITUTION:The carbonizable org. material is coated on the surface of the SiC particles and the particles are so molded that the bulk density of the molding after the carbonization treatment attains 1.7-2.3g/cm<3>. The resulted molding is calcined at about 500-1,200 deg.C in a nonoxidative atmosphere to carbonize the above-mentioned org. material. The molding after the treatment is then brought into contact with the molten Si at >=1,450 deg.C. The carbide of the org. material in the molding is thereby converted to the SiC and further, the Si is penetrated therein. The porous conductive material consisting of the SiC molding which contains the Si uniformly distributed to a three-dimensional network state by forming independent phases and has fine open cells is thereby obtd. This material is capable of forming an electrode for dry etching which is highly resistant to corrosion and heat and withstands longterm use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porous conductive material with good corrosion resistance, a method for producing the same, and a dry etching electrode using the above material.

[Conventional technology]

The process of etching IC elements on silicon wafers has traditionally been carried out mainly by wet etching, but in recent years there has been a shift to dry etching, which has better productivity and processing accuracy. There are various methods of dry etching, but the mainstream is one in which a gaseous organic halogen compound turned into plasma is used as the etching gas. In this method of dry etching, the silicon wafer is etched with etching gas that is turned into plasma by a plasma discharge electrode placed opposite the silicon wafer being processed. Conventionally, the discharge electrode is made of metal or carbon. are used. In order to generate plasma evenly, the discharge electrode has many small holes for the etching gas to pass through, and although it is extremely expensive, it will be eroded by the corrosive etching gas in a short period of time, and its function will be lost. It gets damaged and must be replaced frequently.

For this reason, the cost of replacing the electrodes occupies a large proportion of the cost of dry etching.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electrode that has better corrosion resistance than conventional dry etching electrodes and can withstand long-term use, thereby making it possible to reduce the cost of dry etching.

Another object of the present invention is to provide a corrosion-resistant porous conductive material that is useful for uses other than the dry etching electrode described above.

[Means to solve the problem]

The present invention, which has succeeded in achieving the above object, is a porous conductive body made of a silicon carbide molded body containing silicon that forms independent phases and is uniformly distributed in a three-dimensional network, and has fine continuous pores. The present invention provides a conductive material and a dry etching electrode made of the conductive material.

The present invention also provides a particularly advantageous manufacturing method for the conductive material, that is, coating the surface of silicon carbide particles with a carbonizable organic substance, and converting the coated silicon carbide particles into a molded product having a bulk density of 1.7 after the organic substance carbonization treatment described below. ~2.3(/e+
m3, the obtained molded body is fired in a non-oxidizing atmosphere to carbonize the carbonizable organic matter in the molded body, and then the treated molded body is heated with molten silicon at 1450°C or higher. A porous conductive material characterized in that the organic carbide is converted into silicon carbide by contacting the molded body and infiltrating the molded body with silicon in an amount greater than the amount necessary to convert the organic carbide in the molded body to silicon carbide. The present invention provides a method for manufacturing.

FIG. 1 shows a cross section of the porous conductive material of the present invention.

Silicon carbide portion 1 accounts for about 80-98% by weight of the total,
It forms a strong three-dimensional mesh skeleton. The silicon phase 2 moves inside the silicon carbide portion 1, with some of it appearing on the surface.
It is also distributed in a three-dimensional network, and the material of the present invention exhibits electrical conductivity due to the presence of this silicon phase.

Although the material of the present invention should not have silicon phases in the form of independent strips that are not integrated into a three-dimensional network,
It is necessary that it contain a sufficient amount (preferably 2% by weight or more) of an integrated silicon phase, thereby exhibiting electrical conductivity as a whole. The pores 3 are preferably all of the open type, imparting sufficient air permeability to the material and allowing gas contact with the silicon phase exposed within the pores.

When used as a dry etching electrode, particularly preferred materials have the following characteristics.

Electrical specific resistance: 200 Ω・cm or less Amount of pores: Approximately 15 to 50 vol. 6c113cm/c
lI2・sec-cm! 120 bulk density: 1.8-2
, 7 g/cm"Bending strength: 1.5-15 kg/+
*m” Heavy metal (iron, chromium, copper, etc.) content: 1100p
Below, the method for manufacturing the above-mentioned conductive material will be described in detail.

Silicon carbide particles are commercially available as abrasive materials, and can be used as they are as the raw material silicon carbide in the production method of the present invention. Generally, the larger the particle size of silicon carbide, the larger the pore size of the product, so the particle size of the silicon carbide to be used is appropriately selected depending on the desired pore size of the product. When making dry etching electrodes, the preferred silicon carbide particle size is about 300 microns or less. Incidentally, since it is desired that the dry etching electrode has as low a heavy metal content as possible in order to avoid heavy metal contamination of the silicon wafer, it is desirable to use silicon carbide as a raw material with a low heavy metal content.

Carbonizable organic substances used for coating silicon carbide particles include those that dissolve in water or organic solvents to form a solution that can be coated and that carbonize in high yield when fired in a non-oxidizing atmosphere, such as phenol resins. , thermosetting resin such as furan resin or pitch is used.

Coating can be performed by thoroughly mixing a solution of a carbonizable organic substance and silicon carbide powder using a stirrer, and then heating and drying the mixture while continuously stirring. It is also possible to use a fluidized bed coating method. The coated carbonizable organic material is carbonized in the next firing step, and the formed carbide becomes a reaction target for molten silicon, so the preferred coating amount of the carbonizable organic material varies depending on the carbon yield of the carbonizable organic material used. Therefore, the overall preferred coating amount is suitably expressed in terms of carbide amount, which value is from 3 to 15%, particularly preferably from 5 to 12%, based on the weight of silicon carbide. If it is less than 3%, the carbon coating formed on the silicon carbide particles cannot become a continuous phase, and therefore only a product with low strength is obtained in which the silicon carbide particles are insufficiently bonded by the silicon carbide produced in the reaction. Also 15
% or more will only reduce the porosity of the product.
It's useless.

In addition, in the coating step, an auxiliary agent for improving moldability in the next molding step may be attached to the silicon carbide particles together with the carbonizable organic substance. Suitable auxiliaries include those that thermally decompose and scatter at temperatures below the carbonization temperature of carbonizable organic substances, such as paraffin, wax, stearic acid, and thermoplastic synthetic resins (such as acrylic resins and methacrylic resins). be.

The required amount of coated silicon carbide particles is put into a mold and compression molded using a uniaxial press, etc. In this case, the molding conditions are such that the bulk density of the molded product after organic carbonization treatment is as follows. 1.7~2.31/cm". If the bulk density is less than 1.7 cm3 (7 cm3), it will be difficult to obtain a product with the strength required for practical use. On the other hand, If the density exceeds 3 g/cm3, it becomes difficult to obtain a porous material because silicon enters the interparticle voids that become smaller accordingly.The bulk density of the molded object is determined by the molding pressure, A desired value can be obtained by adjusting the molding temperature and the like.

The obtained molded body was first heated in a non-oxidizing atmosphere to approximately 500 to 1
The molded body is heated to 200° C. to carbonize the carbonizable organic matter in the compact (if a decomposable molding aid is used, it is decomposed prior to carbonization of the carbonizable organic matter). Since carbonization of carbonizable organic matter accompanies the liberation of volatile substances, the formed carbide has many fine interconnected pores.

Thereafter, the molded body is heated to 1450° C. or higher, which is the melting point of metal silicon, preferably about 145° C. in a vacuum or in an inert gas.
Heat to 0°C to 1700°C and contact with molten silicon. Methods for this purpose include raising the temperature while the molded body is buried in powdered metal silicon, or applying a paste of metal silicon powder with an appropriate binder to the surface of the molded body and raising the temperature. , a method in which a metal silicon powder molded into a sheet shape is heated while it is in contact with a molded body. At this time, the molten silicon enters the continuous pores of the organic carbide portion of the molded body by capillary action, and then reacts with carbon to produce silicon carbide. The amount of silicon required to convert all of the organic carbide into silicon carbide is usually around 2.5 times the weight of the organic carbide, so when producing the conductive material of the present invention, a larger amount of silicon must be infiltrated. Therefore, it is necessary that unreacted silicon desirably remain in an amount of 2% by weight or more based on the entire material. If there is too little unreacted silicon, a three-dimensional network silicon phase will not be formed and the required conductivity will not be obtained.

When the organic carbide portion is converted into silicon carbide as described above, the silicon carbide particles originally present in the compact are produced by this reaction and become integrated with the silicon carbide and the unreacted silicon. Most of the voids between silicon carbide particles that existed in the molded body before treatment remain as voids. Through the above steps, the porous conductive material of the present invention, which is a silicon carbide molded body having a three-dimensional network silicon phase, is formed.

Example 1 900 g of silicon carbide particles with an average particle diameter of 100 μm were
The silicon carbide particles were coated with the phenolic resin by mixing the mixture with 100 g of a novolac type phenolic resin dissolved in 0 ml of acetone in a mixer equipped with a stirrer, and heating the mixture with subsequent stirring to evaporate the acetone.

Next, 1 ton/cm of coated silicon carbide
The molded product was molded into a plate shape under a pressure of 100 ml, and the resulting molded product was fired.

The molded body after firing has a weight of 35.4 g and a bulk density of 1.
It weighed 84 g7cm3 and consisted of 94% by weight silicon carbide and 6% by weight resin carbide.

This fired compact was heated under vacuum while in contact with 7.1 g of metallic silicon powder (330% of the 2.12 g of carbon in the compact) and kept at 1500°C for 2 hours to melt it. Most of the silicon was infiltrated into the molded body.

After this infiltration treatment, the porous molded body obtained by cooling was
．． More than 7% by weight consists of silicon carbide, and the pore size is 70-1
60μ, pore volume 30 vo1%, air permeability 0.09cri
・cm/c♂・sec-cmB, o, specific conductivity 35Ω・
It had a bending strength of 8.5 kg/c♂.

〔Effect of the invention〕

As mentioned above, the plasma discharge electrode needs to have corrosion resistance against etching gas and air permeability, and the material of the present invention exhibits sufficient corrosion resistance and heat resistance because it is made of silicon carbide and silicon. Moreover, since it is porous, it has breathability even without special perforation. Further, since the conductivity of the material of the present invention is not due to metal but due to the silicon phase, there is no problem of liberating heavy metals and contaminating the silicon wafer during use.

Taking advantage of the above characteristics, the material of the present invention can be used in various fields other than dry etching electrodes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the porous conductive material of the present invention. l: Silicon carbide part 2: Silicon loss 3: Pore part Figure 1

Claims (3)

[Claims] (1) A porous conductive material comprising a silicon carbide molded body containing silicon that forms independent phases and is uniformly distributed in a three-dimensional network, and has fine continuous pores. (2) The surface of silicon carbide particles is coated with a carbonizable organic substance, and the coated silicon carbide particles have a bulk density of 1.7 to 2.3 g/c after the organic substance carbonization treatment described below.
m^3, the obtained molded body is fired in a non-oxidizing atmosphere to carbonize the carbonizable organic matter in the molded body, and then the molded body after treatment is heated to 1450°C or higher to melt silicon. Claim 1, characterized in that the organic carbide is converted into silicon carbide by contacting with the molded body to infiltrate into the molded body an amount of silicon in an amount greater than that required to convert the organic carbide in the molded body to silicon carbide. A method for producing porous conductive materials. (3) A dry etching electrode made of the conductive material according to claim 1.