Conversion of high purity silicon powder to densified compacts

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...

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 utilized to produce silicon feed stock for other applications. It is a further object to provide a process and technology that will maintain the purity of the silicon to nearly the same level as the starting silicon powder.

[0009] It is another object of the invention to provide a system and facility for conducting a powder-to-compact conversion on a commercially useful production rate, such as high speed compacting and densification, and processing upwards of 25 kg or more of silicon powder per hour.

[0010] The most important aspect of this invention is the development of a process that provides silicon feed stock material to user industries while maintaining the product purity very close to that of the starting material. In particular, when used with the high purity silicon powder from the electronic industry it adds significant value to the material and provides a feedstock to the photovoltaic industry. In the present invention the silicon compacts can be produced in regular geometric shapes. Typically, the silicon used for crystal growth comes in irregular chunks or granules. The advantages of regular shaped silicon of this invention provide for better packing possible, whether for transportation purposes or in the crucible used for melting silicon prior to growing crystalline silicon ingots.

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 to convert silicon powders to forms that keep the purity of the product close to the initial powder quality, can be produced in a manufacturing environment, and, more importantly, be transported without form failure to subsequent product users.

There is also no known industrially useful and practical methodology to convert high purity silicon dust and powder to high purity densified silicon compacts that can be used as significant polysilicon feedstock for photovoltaic industries.

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