US Patent 7226881 Ultra low thermal expansion transparent glass ceramics

There are provided glass-ceramics having an ultra low thermal expansion property and super flat surface capable of coping with lithography for the next generation LSI and component parts for semiconductor equipment such as masks, optical reflecting mirrors, wafer stages and reticle stages and various precision parts using such glass-ceramics. Glass-ceramics of the invention have an average linear thermal expansion coefficient within a range of 0.0±0.2×10−7/° C. within a temperature range from 0° C. to 50° C., have difference between the maximum value and the minimum value of ΔL/L of 10×10−7 or below, and comprise SiO2, Al2O3 and P2O5 with the total amount thereof in mass % being within a range from 86.0% to 89.0%.