Arbitrary three-dimensional micro-fabrication by polymer grayscale lithography

Abstract

We report on the continuing development of a grayscale lithography technique based on the use of a polymeric grayscale photomask. Arbitrary three-dimensional (3D) microstructures can be realized in positive and negative photoresist materials by the use of the polymeric grayscale photomask with standard ultra-violet (UV) lithography. The fabrication of such 3D structures depends on the differential absorption of in photo-absorbing material. The photomask is made of patterned polydimethylsiloxane (PDMS) polymer doped with a UV absorbing laser dye. The PDMS photomask contains micro-patterns made by micro-molding the PDMS on a complementary silicon master mold. By adjusting the thickness of the patterns on the polymer photomask, the dopant dye concentration in the photomask and UV exposure dose, a multitude of unique 3D microstructures can be fabricated on the substrate with desired geometries and dimensions. While the feasibility of grayscale lithography with such a polymeric mask has been reported by us earlier, this paper describes the fabrication of master mold and polymeric grayscale photomask.