PHOTOLITHOGRAPHY WITH TRANSPARENT REFLECTIVE PHOTOMASKS

A new type of photomask was fabricated by casting a prepolymer of a tr ansparent, elastomeric polymer (polydimethylsiloxane, PDMS) against a Si(100) master whose surface has been patterned with V-shaped trenches or pyramidal pits using anisotropic etching. The PDMS replica, when p laced in contact with a him of photoresist and illuminated, acts as a photomask, The sidewalls of the trenches and pits in the silicon maste r meet with the plateaus in dihedral angles of 54 degrees; as a result , the PDMS replica selectively blocks the incident light in regions wh ere it has sloping features by total internal reflection, and acts as a reflective contact mask for photolithography. The feasibility of thi s new type of photomask has been demonstrated by the fabrication of mi cropatterns in photoresist (and in an underlying silicon substrate) wi th smaller feature sizes and higher complexities than those present on the original chrome mask used in patterning the silicon master. The. patterns produced using these elastomeric photomasks can be changed by varying the pressure applied in contacting them. (C) 1998 American Va cuum Society.