Triton Surfactant as an Additive to KOH Silicon Etchant

Anisotropic etching of Si (100) and (110) planes in alkaline solutions containing the nonionic surfactant is studied in this paper. Triton X-100 surfactant, normally used for the modification of TMAH (tetramethylammonium hydroxide) etchant, is added to KOH (potassium hydroxide) solution. As a result, the (100) and (110) etch rates are significantly reduced and the etch rate ratio is obtained. The influence of KOH concentration (at 10 and 100 ppm (v/v) of the surfactant) on the etching process is also investigated. Low roughness of (110) surface is achieved in the 2M KOH solution containing Triton. The smooth {110} sidewall planes inclined at 45° toward the (100) substrate are fabricated by etching in the KOH + Triton solution. The 45° {110} sidewalls are potentially attractive as MEMS micromirrors for optical beam reflection at an angle of 90°. The low etch rate of (100) plane is kind of a disadvantage of the fabrication method, but it can be fairly overcome by elevating the process temperature and stirring the etching solution.