Multi-phase photo mask using sub-wavelength structures

摘要

A phase shift mask using sub-wavelength structures for use in lithography wherein a layer of a first transmissive material being of a first phase is provided. A layer of a second transmissive material being of a second phase is also provided. Disposed in the transition between the first and second regions is a plurality of subwave-length periodic structures. The structures have a first and second side. The structures are shaped such that the effective refractive index along the first sides approximates the refractive index of the first transmissive material and the effective refractive index along the second sides approximates that of the second transmissive material. This arrangement results in a gradual change in the effective refractive index from that of the first transmissive material along the first sides to that of the second transmissive material along the second sides. This gradual change in effective refractive index further results in a gradual phase change from the first phase at the first sides to the second phase at the second sides thereby substantially eliminating the intensity nulls associated with the phase change transition.