| 摘要 |
PURPOSE:To prepare large sized quartz glass useful for photomask base plate with good yield by converting a porous glass parent material deposited and grown on one end of a seed rod and converting it gradually to transparent glass by heating from its foot end. CONSTITUTION:A heating furnace 21 provided with an annular heater 22 in the inside (capable of heating to ca.1,200 deg.C at the top, to ca.1,430 deg.C at the intermediate part, and to ca.1,400 deg.C at the bottom) is used. A porous glass parent material 11 formed on an end of said seed rod 10 is moved downward in said heating furnace 21 while keeping revolution of the rod. The rod is inserted gradually into the heater 22 from the foot end of the rod, and heated and melted successively forming a quartz glass 23 having a smaller dia. than the parent material 11. When the foot end of the seed rod 10 reaches just beneath the top end of the heater 22, the virification treatment is finished. Accordingly, bubbles generated during the virification stage are discharged to the outside through the upper porous glass parent material, and are not left in the quartz glass 23. Moreover, since the part of the seed rod 10 near the foot end is not melted by heating, the formed quartz glass 23 is held securely until the end of the preparation stage. |
