Dry Etching Continuous Surface Profiles into Infrared Semiconductor Materials

Etching high-efficiency diffractive optical elements (DOES) into InSb substrates, using multiple binary masks, has proven to be problematic. This microfabrication method (sometimes called binary optics technology) is time-consuming, costly, sensitive to alignment errors, and only produces a less-than-ideal DOE. Other major problems, which appear to be unique with InSb and the multi-mask process, are polymer buildup and substrate fracturing in subsequent etch levels. Since these do not appear to be problems with a single etch process, a new process is needed which achieves fabrication of high-efficiency DOEs with only a single mask and single etch step. This proposed effort will investigate the application of gray scale mask technology to etching high-efficiency DOEs in InSb and InAs substrates. New processes appropriate for gray scale masks, including photoresist exposure/development and RIE gas chemistries will be developed. Unique new methods of fabricating gray scale masks will also be investigated. These new processes will be used to fabricate continuous profile DOEs and refractive micro-optical components in III-V semiconductors such as InSb and InAs. BENEFITS: Processes developed under this effort will greatly benefit the production of commercial FLIR and IR detector systems. Potential commercial devices could include radiation hardened focal plane arrays, laser optical limiters for night vision devices, filters and elements for advanced staring FLIR systems, high efficiency/low cost night vision illuminators and spotters, IR detectors, and various applications within the micro-machining industry.