A mask set was fabricated with electron beam lithography using conventional and novel pattern replication techniques. Minimum feature size on the high resolution layer was 0.5 μm. The masks were later used for deep ultraviolet (UV) contact lithography to produce working MOSFET’s with submicrometer channel lengths. Two 0.5 μm level masks were fabricated on quartz plates, one each by two techniques: conventional chromium wet etching, and a new technique utilizing ion implanted polymethyl methacrylate (PMMA) as the masking medium. In this unconventional method, a PMMA coated quartz plate was exposed by an electron beam and developed to leave 0.5 μm features on a clear background. The subsequent bombardment of the patterned PMMA with 200 keV Si+ created a film which is opaque to near and deep UV, making it a suitable masking medium for conventional and deep UV photolithography. During the ion bombardment, the PMMA undergoes significant structural change, becoming harder, optically denser, and more adherent to the quartz substrate. A 0.5 μm feature size mask of the same polarity was also made using electron beam patterning of PMMA and wet etching of the underlying chromium. A mask set was also fabricated with a minimum feature size of 1.0 μm. In this level, the 1 μm clear areas were surrounded by opaque chromium areas after wet chemical etching. This mask set was used for conventional contact photolithography in the fabrication of working NMOS devices.