| Sub-micron optical gratings are essential integrated elements to couple light into waveguides and for optical monitoring of microfluidic channels or MEMS devices. Since the required features in the sub-micron regime are difficult to achieve by mechanical ruling and photolithography, alternate fabrication techniques are investigated. Exposure by e-beam and laser are two direct write methods which are used. These methods preclude the need of a mask, require few processing steps, and can be used to write features of sizes desired for optical gratings. In this research, we explore and develop processes to create sub-micron gratings by both these methods. A resist bi-layer is patterned by e-beam exposure. After metal lift-off, the grating structure is transferred into silicon by reactive ion etching (RIE). Rectangular gratings with 200nm--500nm feature size and 50% pitch were successfully fabricated. Borofloat, silica and alumina have been etched using chrome as a mask with vertical sidewalls. Grating structures of any pitch can be created in these materials using e-beam writing in resist and RIE. A 255nm copper vapor laser was used to ablate lines in borosilicate glass. |
