EFFECT OF ANODIC BONDING TEMPERATURE ON MECHANICAL DISTORTION OF SIC X-RAY MASK SUBSTRATE

Distortion of SiC X-ray mask substrate during anodic bonding has been found to occur due to the difference in the thermal expansions of SD glass frame and Si wafer deposited with SiC, and the distortion characteristics can be explained by the bi-metal effect. The reduction in the difference in the expansion is required to obtain lower substrate distortion, and has been realized by using the SD-2 glass, which has the most accurate matching of the expansion to Si, and by lowering the bonding temperature. Any other parameters than the bonding temperature, such as the applied voltage and the bonding time, have been found not to cause the distortion. Homogeneously concave mask substrate bonded at 230-degrees-C, using 4-mm-thick SD-2 glass frame and 1-mm-thick wafer, has the flatness values of 2.18 mum and 0.26 mum for the wafer and the membrane area, respectively.