Comparative study of spin coated and sputtered PMMA as an etch mask for silicon micromachining

Polymers can be very good alternatives to SiO₂ and Si ₃N₄, which are normally used to mask the anisotropic etching of silicon in anisotropic etchants like KOH. An adherent PMMA layer can be conveniently used as a mask material as it is cheaper and easy to deposit and remove. In this regard a comparative study of spin coated PMMA with sputtered PMMA as an etch mask for silicon micromachining is carried out. The maximum masking time of 32 min in 80°C 20 wt% KOH was obtained for spin coated PMMA samples, which were prebaked at 90°C. As this masking time is insufficient for fabrication of various MEMS structures, sputter deposition of PMMA films was carried out in which a masking time of 300 min as against to 32 min was obtained under similar conditions