45° micromirrors fabricated by silicon anisotropic etching in KOH solutions saturated with alcohols

Fabrication of micromirrors inclined at 45° towards substrate is studied in this paper. The micromirrors are fabricated by anisotropic etching of monocrystalline silicon in KOH aqueous solutions saturated with different alcohols. The micromirror is formed by {110} sidewall inclined at 45° towards {100} substrate. The influence of propyl and butyl alcohols on etching anisotropy and surface morphology of micromirror structures is investigated. The impact of KOH concentration on micromirrors' parameters is also examined. The results show that the best etching anisotropy is achieved in the solutions with isopropanol and tert-butanol, and at the low concentration of KOH. Although the {110} mirror planes are patterned with stripes in the case of all considered etching solutions, the surface morphology of the {100} substrate is different for different alcohol additives. Contrary to propyl alcohols, the {100} surfaces etched in the solutions with butyl alcohols are densely covered with pyramidal structures (called hillocks). The angle of the micromirror inclination towards the substrate is evaluated by microscopic measurements and compared with the results reported in the literature.