| 摘要 |
A protective dust cover for a photomask or reticle useful for forming semiconductor integrated circuits, which is a transparent thin film cover to be disposed with a certain distance from the substrate surface of the photomask or reticle for the protection and dust proof of the substrate surface, said transparent thin film consisting essentially of a polyvinyl acetal of the formula: <CHEM> wherein R is a hydrogen atom, -CH3, -C2H5 or -CnHmF2n-m+l wherein n is an integer of from 1 to 8 and m is an integer of from 0 to 2n, x is a number of from 5 to 40, y is a number of from 0 to 10, z1 is a number of from 0 to 90/2, and z2 is a number of from 3/2 to 95/2, having a vinyl acetate content of at most 10 mol% and an acetal content of at least 60 mol%. |
