The authors report a new process combining interference lithography with potassium hydroxide (KOH) anisotropic etch technique for fabrication of high aspect ratio silicon gratings on (110) oriented silicon wafers. This new process has the ability in fabricating high aspect ratio silicon gratings with extremely smooth sidewalls over a large sample area. An alignment method was developed to align interference fringes to the vertical (111) planes of (110) oriented wafers. In addition, a room temperature etch process with 50 wt % KOH solution was chosen to finally get an etch anisotropy of 188. Better etch uniformity was achieved by adding a surfactant to the aqueous KOH to promote the release of hydrogen bubbles. To increase latitude in KOH etching process, deposition of aluminum under a sloped angle with respect to the grating structures was utilized to obtain a high duty cycle nitride mask. To prevent the collapse of high aspect ratio grating structures caused by surface tension, a liquid carbon dioxide supercritical point dryer was used in the drying process. The authors successfully fabricated 320nm period gratings with aspect ratio up to 100 on 5-μm-thick silicon membranes on (110) oriented silicon-on-insulator wafers. The sample area is about 50 mm × 60 mm. The roughness (root mean square) of the sidewall is about 0.267 nm.

Date Published: 28 August 2014
PDF: 8 pages
Proc. SPIE 9170, Nanoengineering: Fabrication, Properties, Optics, and Devices XI, 917018 (28 August 2014); doi: 10.1117/12.2058669

Published in SPIE Proceedings Vol. 9170:
Nanoengineering: Fabrication, Properties, Optics, and Devices XI
Eva M. Campo; Elizabeth A. Dobisz; Louay A. Eldada, Editor(s)