A MANUFACTURING METHOD FOR HIGH-PURIFY QUARTZ GLASS WITH LOW OH CONTENT

A manufacturing method of highly pure quartz glass is provided to prevent the deterioration of definition in a dust proof glass having similar thermal expansion coefficient with the substrate quartz glass by removing OH group in a heat-treatment of silica in dry gas atmosphere. A manufacturing method of highly pure quartz glass having less OH contents comprises a step of heat-treatment using He gas having dew pot temperature less than -100°C at a temperature of at least 1,150°C in dry gas atmosphere for more than 10 hours. The dry gas atmosphere is in a state having moisture of 1ppm under the control of dew pot temperature less than -20°C. After the heat-treatment in dry gas atmosphere, an annealing treatment is carried out at virtual temperature of 950-1,000°C. An anti-dust glass for projection display is prepared by a process comprising steps of: drying silica soot; preparing quartz glass ingot by heat-treatment of the dried silica for making a glass state; slicing the quartz glass ingot in a form of wafer by means of wire saw; lapping the slices to quartz glass wafer and polishing the wafer; and preparing anti-dust glass by means of dicing saw. A high-temperature poly-silicone TFT substrate or an opposed substrate is manufactured by a process comprising steps of: drying silica soot; preparing quartz glass ingot by heat-treatment of the dried silica for making a glass state; slicing the quartz glass ingot in a form of wafer by means of wire saw; and lapping the slices to quartz glass wafer and polishing the wafer.