Etching of sub-micron high aspect ratio holes in oxides and polymers

Abstract

Sub-micron holes have been successfully etched into: PMMA/DR-1 on Teflon, BCB, Ta2O5, Nb2O5 and SiO2, with the aim of forming photonic crystal structures. Pattern transfer from the NiCr masks into the material is achieved in an electron cyclotron resonance high-density plasma system, using a combination of the gases: CHF3, CF4, O2, Ar and SF6, and an RF bias on the sample. The etching of Ta2O5 and Nb2O5 is hindered by the high sublimation temperature, approximately 230 °C, of TaF5 and NbF5. This problem was resolved by heating the sample. For these materials aspect ratios of 5 were achieved, with holes of down to 200-nm wide being etched. Wall roughness was typically 30 nm, peak to trough. For SiO2, aspect ratios of 8 were achieved and the wall roughness was about 10 nm, peak to trough. For the polymers: PMMA/DR-1 on Teflon and BCB aspect ratios of 16 are possible for 250-nm wide holes, along with high, 1 μm/min etching rates.