Fluid handling – Processes – Involving pressure control
Patent
1998-04-15
2000-09-12
Chambers, A. Michael
Fluid handling
Processes
Involving pressure control
13756517, 13756523, 13756533, 137208, 137557, 137 6825, F17D 118
Patent
active
061162604
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for stably supplying a liquid material such as a raw-material solution for glass used in fabrication of optical fiber or synthetic silica glass to an evaporator or the like such as a vaporizer, and to a supplying method thereof.
BACKGROUND ART
With recent increase in integration of LSI, micromachining is being developed to form finer patterns utilizing the photolithography technology for exposure and transfer of integrated circuit onto silicon wafer. For that, wavelengths of light source become shorter and shorter and the silica glass, as an optical element of photolithography exposure apparatus, is demanded to have high transmittancy of light in the ultraviolet region and high uniformity of refractive index. In order to realize the high transmittancy of light in the ultraviolet region, it becomes necessary to lower an impurity concentration in silica glass and the flame hydrolysis process is used as a usual synthesizing method thereof.
This flame hydrolysis process includes heating a liquid material as a raw-material solution for glass at temperatures over the boiling point in a vaporization tank or the like to vaporize it, diluting this raw-material gas with a carrier gas such as oxygen, hydrogen and inert gases, and further blowing this raw-material gas, together with burning flame comprised of oxygen and hydrogen or combustible gas, from a burner for flame hydrolysis toward a target of heat-resisting material. Glass particles synthesized by a chemical reaction in this manner are fused into glass, thus synthesizing silica glass.
In the flame hydrolysis process the liquid material such as silicon tetrachloride is used as a raw material for glass, as described above, and it is used in the vaporized form. Accordingly, all metal impurities contained in the raw material for glass are trapped in the vaporization tank without provision of any special distillation device, which means that the raw material for glass is distilled. This permits high-purity raw-material gas to be supplied. In general, an evaporator such as the vaporizer is used as a device for supplying such high-purity raw-material gas.
This vaporizer is a gas control system for supplying the vaporized raw-material gas to a reaction system. Namely, the liquid material is vaporized under an ambient temperature over the boiling point thereof and the flow rate thereof is controlled stably and precisely by a mass flow controller. This vaporizer is basically comprised of a gas control section and a thermostatic bath.
Further, the glass raw material for optical fiber or silica glass is usually selected from liquid materials of silicon compounds such as silicon tetrachloride. This liquid material is supplied under pressure by nitrogen gas or the like from a vessel such as a bomb to the evaporator such as the vaporizer. More specifically, the supply under pressure of the liquid material to the evaporator is carried out by always keeping a constant pressure (approximately 1 to 2 kg/cm.sup.2) in the liquid material vessel through a regulator by nitrogen or inert gas (which may be either one of not only the inert gases in the periodic table, but also gases of low reactivity with the liquid material and which will be called pressure gas hereinafter). This pressurization causes the liquid material to be supplied to the evaporator and the gas is injected into the vessel by an amount of reduction of the liquid material.
A conventional liquid material supplying apparatus of this type is composed of a pressure gas line 10, a material supply line 20, and a vessel 50, as shown in FIG. 1. The pressure gas line 10 is composed of a gas supply pipe 11 through which the pressure gas to be injected into the vessel 50 is fed, a gas inlet pipe 51 fixed to the vessel 50, and a gas line connection pipe 13 having a gas line joint 15, being a joint to this gas inlet pipe 51, at the fore end. Further, the material supply line 20 is composed of a discharge pipe 53 fixed to the vessel 50, a material line connection
REFERENCES:
patent: 5148945 (1992-09-01), Geatz
patent: 5417346 (1995-05-01), Ferri, Jr. et al.
Hiraiwa Hiroyuki
Nakagawa Kazuhiro
Chambers A. Michael
Nikon Corporation
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