Conversion of high purity silicon powder to densified compacts

Inactive Publication Date: 2007-01-18
SEMLUX TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008] It is an object of the invention to provide a viable and practical process and technology to convert silicon powder into a form, typically compacted densified shapes, that can be manufactured, transported and uti

Problems solved by technology

The Fluid Bed process, however, also results in a large quantity of ultra fine silicon dust.
This powder is of high purity, but cannot be recycled or used in silicon melting and crystal growth applications.
The wafers were contaminated with iron, aluminum, carbon and oxygen.
There is no published prior art that purports to utilize a process for effective use of otherwise unusable silicon dust and powder, i.e., there is no robust, industrially practical and cost-effective methodology

Method used

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  • Conversion of high purity silicon powder to densified compacts
  • Conversion of high purity silicon powder to densified compacts
  • Conversion of high purity silicon powder to densified compacts

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0040] High purity Silicon powder is mixed with high purity fumed silica as a binder. Typically, the fumed silica is in the range 0.01-5 weight percent of the silicon powder, preferably in the range 0.05-0.2 weight percent. When added to the silicon powders, fumed silica aids powder flow, by forming a layer on the silicon surface and acts like a lubricant, aiding flow and compression. Due to the hydrophilic nature of the fumed silica it absorbs water off the surface of the particles and prevents caking. The mix is well blended, then formed into compacts or pellets / tablets of required shape. The compacted shape is then sintered in an inert gas or reducing gas such as hydrogen in inert gas or vacuum environment at 1000-1350 C. to produce the compacted densified final product.

[0041] During the sintering operation the fumed silica binder reacts with the silicon matrix to form SiO gas, which vaporizes from the compact. The residual oxygen in the sintered silicon compact is expected to b...

example 2

[0042] High purity Silicon powder is mixed with high purity colloidal silica as a binder. The high purity colloidal silica is nominally 40-50% by weight SiO2 in isopropyl alcohol or toluene. Typically, the colloidal silica is in the range 0.01-5 weight percent of the silicon powder, preferably in the range 0.05-0.2 weight percent. When added to the silicon powders, colloidal silica aids powder agglomeration and particle bonding. The mix is well blended, then dried to remove essentially all carrier solvent, then formed into compacts or pellets / tablets of required shape. The compacted shape is then sintered in an inert gas or reducing gas such as hydrogen in inert gas or vacuum environment at 1000-1350 C. to produce the compacted densified final product.

[0043] During the run up to the sintering temperature any remaining carrier solvent is removed from the compact (FIG. 3). During sintering the silica content of the binder reacts with the silicon matrix to form SiO gas, which vaporize...

example 3

[0044] High purity Silicon powder is mixed with high purity ethyl silicate 40 (polydiethoxysiloxane with 40% SiO2) as a binder. Typically, the ethyl silicate 40 is in the range 0.01-5 weight percent of the silicon powder, preferably in the range 0.05-0.5 weight percent. The mix is well blended, then formed into compacts or pellets / tablets of required shape. The use of ethyl silicate 40 binder requires a de-binder step prior to sintering. Ethyl silicate 40 decomposes completely at >300 C. to silica and ethyl alcohol. The latter boils off the compacted body without any significant reaction with silicon.

[0045] After binder removal the compacted shape is then sintered in an inert gas or reducing gas such as hydrogen in inert gas or vacuum environment at 1000-1350 C. to produce the compacted densified final product. During the sintering step all volatile decomposition products of ethyl silicate 40 will be released completely from the compact. The silica will react with silicon to form s...

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Abstract

This invention describes methods of compacting and densifying high purity silicon powder to defined geometric forms and shapes. High purity silicon powder is first mixed with binder from a select group of binders and pressed into desired shapes in a mechanical equipment. The binder is removed either in a separate step or combined with a subsequent sintering operation. The binders and process conditions are chosen to make negligible change to the purity of the silicon in the end product. When high purity silicon powder is utilized in the process, the end use for the densified silicon compacts is primarily as feedstock for silicon-based photovoltaic manufacturing industries.

Description

RELATED DOCUMENTS [0001] This Utility Patent Application claims priority of a Provisional Patent Application No. US60 / 696,235 dated Jul. 1, 2005, and titled “Powder metallurgical conversion of high purity silicon to densified compacts”.FIELD OF INVENTION [0002] The present invention is directed towards conversion of fine silicon powder into densified silicon compacts for use in silicon melting and alloy industries. This conversion process is achieved by the use of selective binders to aid in compacting the powder towards subsequent sintering and densification. When adapted to high purity silicon powder, the end use for the densified silicon compacts is primarily as feedstock for silicon-based photovoltaic manufacturing industries. BACKGROUND OF THE INVENTION [0003] Compacting of powders is well known in metallurgical and ceramic process industries and is a highly developed method of manufacturing various parts and shapes. In these processes powder metals, ceramics or a mixture of ce...

Claims

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Application Information

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IPC IPC(8): B22F3/12
CPCC01B33/02C04B33/02Y02E10/547H01L31/1804C04B35/584Y02P70/50
Inventor HARIHARAN, ALLEPPEY V.CHANDRA, MOHANRAVI, JAGANNATHAN
Owner SEMLUX TECH
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