Microscope Projection Photolithography for Rapid Prototyping of Masters with Micron-Scale Features for Use in Soft Lithography

This paper demonstrates the application of projection photolithography, using a standard commercial microscope, for the generation of masters for soft lithography. The procedure is rapid and convenient and produces features smaller in size (as small as 0.6 μm) than those available from other methods of rapid prototyping, albeit over a limited area (∼4 × 104 μm2 per exposure). A transparency photomask (prepared using high-resolution printing) is inserted into the light path of the microscope and projected through the microscope objective onto a photoresist-coated substrate. Features on the order of 1 μm can be produced routinely over the area of sharp focus (a circle of radius r ≅ 100 μm with a 100× objective) by this method without modification or precise calibration of the microscope. The microscope platform also provides two other useful functions, both characteristic of commercial steppers: step-and-repeat exposures and pattern alignment. The developed photoresist is used as a master for the fabrication of stamps and replica molds for soft lithography. These elements are used in demonstrations of fabrication of microstructures with feature sizes in the range from 1 to 10 μm. Although the technique is limited in the area it can produce in a single exposure, it can fabricate many kinds of structures useful in chemistry, biology, and materials science.