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In Situ Particle Removal for Silicon Wafer Processing

IP.com Disclosure Number: IPCOM000081710D
Original Publication Date: 1974-Jul-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Chou, NJ: AUTHOR [+4]

Abstract

During the processing of silicon wafers, particles may escape a filtering system, and thereby enter the processing tube in the gas stream. A method of in situ removal of such particles by electrostatic precipitation using high-purity polycrystalline silicon electrodes is described. The use of polycrystalline silicon is central to this method, since it is the only electrically conducting material that does not act as a contaminant during high-temperature processing of silicon devices.

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In Situ Particle Removal for Silicon Wafer Processing

During the processing of silicon wafers, particles may escape a filtering system, and thereby enter the processing tube in the gas stream. A method of in situ removal of such particles by electrostatic precipitation using high-purity polycrystalline silicon electrodes is described. The use of polycrystalline silicon is central to this method, since it is the only electrically conducting material that does not act as a contaminant during high-temperature processing of silicon devices.

A sketch of the arrangement is given in Fig. 1 where a central rod 1 is biased with respect to a concentric cylinder 2. Both the rod 1 and the outer cylinder 2 (whether a solid tube, a tube liner, or a coating on a fused silica tube) are made of polycrystalline silicon. The wafers 3 set inside the outer cylinder 2 and are electrically isolated from the rest of the system by a quartz boat 4.

Small particles are generally electrically charged especially in very dry, water- free ambients; however, if needed, the particles can be charged prior to entering the tube by either an aerosol type nozzle entrance or by radioactive bombardment. A high voltage, which is limited by the maximum breakdown strength of air (approx. 30,000 volts/cm) but seldom exceeds 2000 volts, is applied between the walls of the furnace tube 2 and the rod 1 situated in the center of the furnace tube. With an electric field of appropriate magnitude, the particles can thus be removed electrostatically before they have a chance to impinge on the surface of the silicon wafers 3.

In addition to the magnitude of the applied field, the charge-to-mass ratio is an important factor in the effective removal of particles. Since the ratio increases for small particles, the proposed scheme for in situ removal, in fact, favors the deletion of submicron particles, which are the...