Viscosity tailoring of fused silica

Details Viscosity tailoring of fused silica Viscosity tailoring of fused silica

1999-11-19

2001-05-22

Marcantoni, Paul (Department: 1755)

Compositions: ceramic

Ceramic compositions

Refractory

C385S066000, C313S002100

Reexamination Certificate

active

06235669

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to synthetic fused silica for use in semiconductor applications. Particularly, this invention relates to synthetic fused silica for preparation of elongated fused quartz members. More particularly, this invention relates to synthetic silica for use in tubing and rods for semiconductors. Furthermore, this invention relates to synthetic fused silica having a viscosity of between 10
14.5
to 10
15
at 1,100° C. for use in a variety of embodiments.
Throughout the specification, numerous references will be made to the use of fused silica in semiconductor applications; however, it should be realized that the invention could be applied to many industries requiring synthetic fused silica having a higher than normal viscosity.
Fused silica has been used in metal-halide, halogen and mercury lamps because of its excellent mechanical strengths and its ability to handle high operating temperatures. In addition, fused silica is becoming an important constituent of the ever-expanding semiconductor and fiber optics industries. Its high purity and resistance to high temperatures are particularly desirable characteristics.
One difficulty in the use of fused quartz in the semiconductor industry is the level of impurities (30-50 ppm). Accordingly, synthetic silica has been experimented with as a replacement to natural silica for some applications. However, a difficulty often encountered in utilizing the synthetic material is its low viscosity. Although a low viscosity may benefit fabricators who rework fused silica products, many fabricators require a fused silica having a higher viscosity. The semiconductor industry is an example of an industry which requires a high viscosity, low impurity fused silica.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of this invention to provide a new and improved synthetic fused silica.
It is a further object of this invention to provide a new and improved synthetic fused silica having a viscosity above 10
14.5
poise at 1,100° C.
A still further object of this invention is to provide a new and improved process for preparing a synthetic fused silica having a tailored viscosity.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects in accordance with the purpose of the invention, as embodied and broadly described herein, the synthetic fused silica of this invention comprises a mixture of synthetic silica and aluminum and has a viscosity of at least 10
14.5
poise at 1,100° C. Preferably, the fused synthetic silica comprises a mixture of silica and at least 7 parts per million aluminum.
The synthetic fused silica mixture is formed by combining synthetic silica and alumina. Typical synthetic silica includes trace amounts of impurities such as alkali metals and hydroxyl groups. In a further preferred embodiment, the mixture comprises a ratio defined as R=Al
2
O
3
/(Li
2
O+Na
2
O+K
2
O+H
2
O) wherein R is greater than or equal to 0.5 and R is less than or equal to 4.0. More preferably, R is greater than or equal to 1 and less than or equal to 1.25.


REFERENCES:
patent: 3764286 (1973-10-01), Antczak et al.
patent: 3806570 (1974-04-01), Flamenbaum et al.
patent: 4028124 (1977-06-01), Bihuniak et al.
patent: 4047966 (1977-09-01), Bihuniak et al.
patent: 4180409 (1979-12-01), Mansmann
patent: 5096857 (1992-03-01), Hu et al.
patent: 890330611 (1991-08-01), None
patent: 69142456 (1996-01-01), None
Manufacture of heat-resistant quartz glass. Chemical Abstracts, vol. 116, Ref. No. 240607k, Feb. 17, 1992.

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