Paper reports the use of a new surfactant NCW-1002 as an addictive in TMAH wet anisotropic etching to improve the
etching characteristic on three silicon principle planes (i.e. (100), (110), (111) planes). Concentrations of TMAH from
2.5% to 10% with addition of various concentration of NCW-1002 are studied to find an optimal combination for a
improved smoothness and etch selectivity between (100) and (110) planes, which is necessary for the formation of
45°mirror plane (110) in (100) silicon surface. Etch rate and roughness of silicon planes were measured by Dektak II and
AFM respectively. Besides, this paper will explain the formation of 45°slope. By improving the selectivity or extending
the etching depth, we are able to enlarge the 45°portion on the mirror surface.
Paper reports improved results in the fabrication of 45° micromirrors using low concentration of TMAH with NCW-601A surfactant. 45° micro mirror is an essential component for obtaining 90° out-of-plane reflection of the optical beam. TMAH anisotropic wet etching on (100) silicon wafer with features aligned to the flat so that 45° slope is formed on (110) plane. This requires the etch rate of <110> planes to be lower than <100> planes. Etching rate selectivity depends on: temperature, concentration, and additives. Substantial undercutting of mask needs to be taken into consideration during the design. TMAH concentrations ranging from 2.5% to 10% with different concentrations of surfactant have been studied to achieve improved smoothness of the micromirror surface and better selectivity. SEM/AFM measurement show the roughness of mirror is less than 1nm. Results also show that the surface roughness varies along the 45° slope with the roughest portion at the top of the mirror. This paper will describe the techniques to reduce the size of the rough portion of the mirror.
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