Browse Prior Art Database

Fabrication of heavy-walled fused silica tubing

IP.com Disclosure Number: IPCOM000012111D
Publication Date: 2003-Apr-09
Document File: 4 page(s) / 29K

Publishing Venue

The IP.com Prior Art Database

Abstract

This disclosure relates to raw materials processing techniques and fusion processing methods that allow fabrication of heavy-walled glass tubing with a low bubble content.

This text was extracted from a Microsoft Word document.
This is the abbreviated version, containing approximately 37% of the total text.

Fabrication of heavy-walled fused silica tubing

ABSTRACT

This disclosure relates to raw materials processing techniques and fusion processing methods that allow fabrication of heavy-walled glass tubing with a low bubble content.�

Fabrication of heavy-walled fused silica tubing

I.                   OBJECT OF INVENTION

The object of this invention is to circumvent processing challenges associated with fusing silica sand in the fabrication of a low bubble content glass.� The primary challenges are: 1) the likelihood of bubble formation (driven by surface contamination) due to both the choice of sand and handling methods involved and 2) the cost, cracking issues, and exposure to contamination associated with the use of a dissimilar material insulation package.

This invention relates to raw materials processing techniques and fusion processing methods that allow fabrication of heavy-walled SiO2 glass tubing with low bubble content.� The main objective is to use fused silica rod as a starting material for re-fusion in a rotary arc fusion machine.� The rod provides a raw material that has very low bubble content itself while further processing methods remove bubbles that form between the interfaces of the rod segments.� The end result is a low bubble content, heavy-walled tube that is suitable for use in semiconductor wafer processing equipment.

II.                PROBLEM TO BE SOLVED

One method of forming a heavy-walled (25mm +) fused silica tube involves loading (depositing) silica sand onto the inner diameter of a rotating cylinder.� This cylinder is typically made from steel or a similar type of alloy and oriented horizontally with its longitudinal axis parallel to the floor.� Once the sand has been deposited, heat is applied to the inner surface of the rotating cylinder in order to melt the sand and form a glass.� Upon cooling the entire system, the resultant shape of the fused glass is a tube, which is removed from the cylinder to be prepared for final processing steps.

Low bubble content within the fused glass is an important specification for the use of this material in semiconductor wafer processing equipment.� Several processing variables present challenges to fusing heavy-walled glass tubing that meets these specifications.� First, the silica sand raw material must be free of entrained air and contamination.� That is the bulk purity must be relatively high.� Second, the surfaces of the sand particles must be free of contaminants.� Finally, the design of the fusion equipment must handle the sand in a way that minimizes surface contamination “pick up”.� This equipment must also provide a means for controlling the melting process so that the alloy cylinder remains intact and does not melt as well.

Due to its relatively small particle size, silica sand can be easily loaded into the rotating cylinder using pneumatic conveying.� While this technique of “spraying” sand particles onto the inner diameter of the cylinder can be well controlled to provide a uniform sand lay...