Fabrication of monolithic diffractive optical elements by the use of e-beam direct write on an analog resist and a...

We present a method to fabricate high-quality and environmentally rugged monolithic diffractive optical elements (DOE's). Analog direct-write e-beam lithography was used to produce analog resist profiles that were transferred into their substrates by the use of chemically assisted ion-beam etching (CAIBE) in one single etching step. An iterative method was used to compensate for the proximity effect caused by electron scattering in the resist and from the substrate during the e-beam exposure. Slope-dependent differential etch rates that occur during the transfer process were characterized and compensated for. Finally, the DOE was divided into regions with different period ranges, and the exposure dosages were set to achieve even and accurate etch depths in the final element. The presented fabrication method will increase manufacturability and reduce processing time, which will result in a general cost reduction per element.