US Patent 7135257 Multi-step phase shift mask and methods for fabrication thereof

A phase shift mask comprises a transparent substrate having a patterned opaque material layer formed thereupon to form a non-transmissive region of the transparent substrate and an adjoining transmissive region of the transparent substrate. A pit is formed within the transmissive region of the transparent substrate. The pit has a stepped sidewall such as to provide the phase shift mask with enhanced optical performance. The phase shift mask may be fabricated employing a self aligned method.