DE2443668A1 - Sawing wire for very fine cutting - produced by formation of hard crystals on wire surface from gas phase - Google Patents

Abstract

Sawing wire for veery fine cutting of e.g. semiconductors is produced by forming hard crystalsa on the wire surface by crystallisation from the gas phase. The wire is pref. made from W,M Mo,Ta,Os, Re or their alloys. The crystals consist of boron, borides, nitrides or carbides. The hard crystals firmly adhere to the wire so that cutting efficiency is much higher than in the known process in which the wire is passed through a suspension of abrasive particles, e.g. diamond or alumina, which only loosely adhere to the wire.

Description

Metal saw wire Metal saw wire When sawing hard materials In many cases, a method is used in which a metal wire is passed through a Running suspension that contains well-matched particles that attach to the wire and accompany him to the workpiece, which under suitable pressure with the saw wire in Comes into contact and then subject to processing by the particles, causing a saw cut is obtained. This sawing process was inter alia. already for sawing of semiconductor materials used, the saw wire usually made of tungsten and the particles of diamond chips or aluminum oxide particles attached to it and the like. exist.

The advantages of this known method are the possibility the achievement of very narrow saw cuts when working with very thin tungsten wire works, and a very dense accumulation of particles from the suspension with the result low material losses.

The disadvantages of this known method are that the Adhesion of the working particle is so slight that it can be easily detached from the wire if the saw hits the workpiece. This reduces the sawing speed and increases it the wear of the saw wire.

In the present invention it belongs to the particles through Replace crystals of a selected material through a chemical reaction are formed and are permanently attached to the wire surface in that the saw wire, which is heated by a flowing electric current through a reaction chamber occurs that contains gaseous substances that by means of thermal Decomposition or reduction forms hard crystals on the saw wire surface, which are well suited for sawing purposes.

As active substances you can preferably boron, borides, nitrides or Choosing carbides A core wire made of a material with a high level of material is suitable as a core wire Tensile strength, such as B.

Tungsten, molybdenum, tantalum, osmium, rhenium or alloys of these Fabrics.

The technique of coating has been known for a long time and in literature Ue a. in Powell's book, Vapor Plating Rails John Wiley Sons, New York, 1955.

Plating in the gas phase is commonly used to produce a Surface has special mechanical, chemical, electrical or optical properties The goal of coating technology is to give it a very dense and smooth To achieve coating During the development of the subject matter of the invention, a Modification of the coating technique just described to implement the inventive idea as necessary and in an opposite way to previous practice Direction With regard to the fact that on the surface one by pulling recovered metal wire always have microscopic bumps these microscopic bumps are used directly to prevent condensation of cores on the wire surface where the conditions for crystal formation are reached cheaper than in the area. With slow crystallization with high According to the invention, it is mainly the primary crystals that grow at temperature have formed in the aforementioned condensation nucleus, in size and does not occur a notable formation of new primary crystals This slow crystallization can be achieved by working with low concentrations of one or more components get the proportions in the reaction gas set0 This can be done z.

B. obtained by dilution with Dzert $ as by a considerable Excess of a component or by reduction of the total pressure the gaseous mixture. Lowering the temperature generally also leads a slow response rate. But there is also the speed the crystallization is decreased, many small crystals are obtained.

Good adhesion of the crystals on the wire is ensured by the fact That favors some atomic diffusion between the wire and that on the wire The crystal formed takes place in a delimited zone, the thickness of which is only atomic dimensions must have.

If the atoms of the surface crystals diffuse too deep into the wire, then this can create a strong bond between the crystal surface and the wire result; But it can also - as studies have shown - lead to an undesirable one Wire brittleness, because new phases are observed that are caused by a Reaction between the atoms of the wire and the atoms of the diffusing substance causes wind.

This brittleness is caused by poor flexural strength and tensile strength noticeable, which is a major disadvantage for the tasks to be solved with the saw blade represents, especially as far as it concerns wires of very small dimensions. There As the degree of diffusion increases with temperature, this phenomenon can be traced take advantage of the fact that the diffusion does not take place too deeply into the wire. if the temperature suitable for preventing such diffusions is too low is to still allow a formation of suitable surface crystals, then can choose a material for the wire in which the amount of diffusion is lower or, if this is not possible, the wire with a surface layer first a substance that causes the diffusion of the atoms of the surface crystals prevented. If you z. B. selects tungsten or molybdenum as the core wire, then the Reaction temperature for the formation of large surface crystals of titanium carbide (TiC) or titanium nitride (TiN) so high that an undesired indiffusion of carbon or nitrogen enters.

A metal wire for sawing materials - especially hard ones Materials and for the formation of narrow saw cuts - is therefore characterized by that on the saw wire from a gas phase in a two-stage process crystals hard substances are formed on a support wire, creating two layers be developed, namely a thin one that is closest to the carrier wire and by means of which the atomic diffusion between the carrier wire and the crystals harder Substances is adjusted so that maximum adhesion without embrittling of the carrier wire occurs and that then a second, thicker layer is applied for sawing, the consists of free crystals with sharper corners of another hard substance.

The invention is illustrated by the following examples and the figures 1 - 3 of the drawings explained: Example 1: A molybdenum wire is provided with a diffusion-preventing Layer of titanium carbide 2-5 µm thick by heating up to about 1,40000 inside of 5 seconds in an atmosphere of toluene, titanium tetrachloride and hydrogen gas coated in a mixing ratio of 0.2 s 1:10 at atmospheric pressure, whereupon a crystalline layer of silicon carbide by heating the wire to about 1,200 ° C in an atmosphere of methylchlorosilane and an excess of 20-50 times is precipitated in hydrogen gas at atmospheric pressure, creating a crystal size Up to 10 to with a response time of 30 seconds is achieved, this wire saws solid bodies that are usually machined with silicon carbide, such as B. silicon steel, tungsten etc.

1 shows a schematic longitudinal section through a molybdenum wire a of 100 # at # thickness, covered with an inner layer b of titanium carbide (TiC) uBd over it equipped with crystals of silicon carbide (SiC).

Example 2: A wire made of molybdenum or tungsten is coated with a diffusion-preventing Layer of titanium nitride from 1-5 Strength by heating to about 1,40000 in 5 seconds in an atmosphere of hydrogen gas H2, titanium tetrachloride TRIOL4 and nitrogen in a ratio of 10: 2: 1 at atmospheric pressure, whereupon on top of this layer a crystalline layer of Borders by heating to about 1200 ° C in an atmosphere of boron trichloride and a 20-50 fold excess of hydrogen gas is coated at atmospheric pressure. This is obtained after a reaction time from 45 seconds sharp-edged crystals up to a size of 10 μm. This wire saws the same materials as mentioned in example 1.

Fig. 2 shows the crystal outlines of the surface of a molybdenum wire with a thickness of 100 1, coated with an intermediate layer of titanium nitride (TiN and with crystals of boron (B) on this interlayer.

3 shows a three-dimensional plan view, enlarged approximately 2,200 times to a detail of the piece of wire described with reference to FIG.

Claims (5)

P a t e n t a n s p r ü c h e = = = = = = = = = = = = = = = 1. Metal wire for sawing materials, characterized in that crystals of hard materials through on the metal wire Crystallization from a gas phase are crystallized. 2. Metal wire according to claim 1, characterized in that the crystals hard materials on a carrier wire from a gas phase in a two-step process are crystallized, whereby two layers are formed, namely a thin one and the layer closest to the carrier wire, by means of which the atomic diffusion of the carrier wire and the crystals of hard materials in the sense of maximum adhesion without Embrittlement of the carrier wire is regulated and covered with a second thicker layer for the sawing function, which consists of clear crystals with sharp corners hard substance 3. metal saw wire according to claims 1 and 2, characterized characterized in that the thin intermediate layer has a thickness of one or several µm has. 4. Metal saw wire according to claims 1 - 3, characterized in that that the carrier wire is made entirely or for the most part from one of the metals tungsten, molybdenum, Tantalum, osmium, rhenium or alloys of these metals. 5 metal saw wire according to claims 1 - 4, characterized in that that the hard materials which form the layers on the carrier wire the materials boron, borides, nitrides and carbides are selected0 L. e e r e i t e