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

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, O-2, 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 degreesC, 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 mum/min etching rates. (C) 2004 Elsevier B.V. All rights reserved.