Modified AlAs epitaxial layers for use as pattern transfer masks

The viability of using a thermally oxidised AlAs layer as a robust mask for the transfer of nanometre scale features is reported. Plasma fluorinated A lAs layers were investigated also, but despite selectivities for fluorinate d masks of 100:1 between the mask and GaAs, this technique is currently not suitable for pattern transfer as it produces robust, but non-uniform, inte rmediate masks. In contrast, aspect ratios of 10:1 or greater can be obtain ed with a selectivity of 100:1 between the oxidised layer and GaAs for sub- micron features.