Continuous-tone grayscale mask fabrication using high-energy-beam-sensitive glass

For highest efficiency optical devices, it is desirable to form continuously graded device features. We describe a technique to produce such features through the fabrication of a continuous-tone grayscale mask and subsequent grayscale photolithography. The design of the mask fabrication process is outlined, including the high-energy-beam-sensitive (HEBS) glass electron-beam exposure response characterization, and the generation of an exposure profile with inherent proximity effect correction. Application of the process is demonstrated through fabrication of smooth-facet retroreflectors, with features that are not possible to produce either by a grayscale process that employs discreet gray levels or by anisotropic wet etch techniques. (C) 2004 Society of Photo-Optical Instrumentation Engineers.