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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.

IP.com Disclosure Number: IPCOM000012113D
Publication Date: 2003-Apr-09
Document File: 7 page(s) / 94K

Publishing Venue

The IP.com Prior Art Database

Abstract

An apparatus to enable a practical method for controlling the ambient atmosphere gas during the fusion of a quartz or silica crucible for use in growing silicon crystals.

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Apparatus for controlling crucible fusion atmosphere

ABSTRACT

An apparatus to enable a practical method for controlling the ambient atmosphere gas during the fusion of a quartz or silica crucible for use in growing silicon crystals.

Apparatus for controlling crucible fusion atmosphere

SUMMARY

The idea is for an apparatus to enable a practical method for controlling the ambient atmosphere gas during the fusion of a quartz or silica crucible for use in growing silicon crystals. We do so by providing a hood enclosure that helps provide some confinement in 5 out of 6 directions. We also provide for an in-flow of the selected atmosphere stoichiometry. This inflow is provided through an apparatus which capitalizes on the geometrical position of the source location and provides directed flow down into the interior of the fusion mold. It is this “shower head” or pipe system that allows us to use a directed flow of the source gas. We then balance the other system exhausts, such as from the hood exhaust piping and the vacuum pumping system, against that in-flow. We basically ensure that the atmosphere within the crucible mold is of our choosing and that this atmosphere is drawn into and through the sand bed. In order to accomplish this, it is important that we provide a means of measuring the atmosphere composition that is in the mold. This enables us to define the control methods unambiguously.  

1.         Statement of the Problem        

There is a need to find practical methods to control the ambient atmosphere for crucible fusion. The problem is basically that one has to design the component parts and develop the methods, and select appropriate materials in such a way that the interior of the mold can first be filled with a selected, controlled atmosphere, and second this atmosphere can be drawn into the sand bed, filling all of the interstices between the sand grains. What is meant by atmosphere control is that above the fusion mold, inside of the fusion mold, and within the sand bed are all the same gas composition and that they are as close as practical to the targeted gas composition. This needed for crucible fusion under and in a controlled atmosphere. Fusion of a quartz crucible in at least a Helium atmosphere enables one to utilize the high diffusivity of helium through SiO2. This allows one to fuse crucibles with the minimum amount of bubbles and the bubbles are of a smaller size, on average, than one would obtain from fusing the crucible under air. This is another technical building block to reduce the bubble density in the produced crucible even more. 

In US Patent No. 4,416,680, the technology defined is for the ability to apply vacuum and lowered pressure to the outside surfaces of the fusion sand during the fusion process. It says nothing about controlling the atmosphere. The use of the vacuum system helps to draw the controlled atmosphere into the sand bed but the presence of a vacuum system alone does not allow on...