A phase shifting mask, to be used for the purpose of improving the resolution of a projection lithography system, was fabricated. This type of mask consists of line-space pairs in which every other aperture induces a 180 degree phase shift in the transmitted radiation. In order to obtain this phase shift there must be a thickness difference between the apertures. Etching of the glass mask plate in 3:100 HF to DI water was used to obtain the required • etch depth
