Development of chalcogenide glass photoresists for gray scale lithography

Wet and dry negative etching procedures are evaluated for the fabrication of 3D graded microstructures in As–S based inorganic photoresists. Absorption of light and consequent photostructural changes near the surface layer enhance the chemical resistance of the As–S films. The success of the procedure is demonstrated by fabricating arrays of 12 μm diameter microlenses in a thin As35S65 film using a gray scale Cr mask and wet etching. The selectivity of dry etching is successfully realized by using photodiffusion in Ag–As2S3 bilayer structure. In this case, however, surface roughness or ‘grass’ is observed after etching. An unexpected segregation of silver is observed at the edges and at the boundary between the exposed and unexposed regions, which is investigated by SEM and XPS.