Small aperture fabrication for single quantum dot spectroscopy

A simple fabrication method for submicron diameter metallic apertures using negative electron beam resist and metal lift-off has been developed. In ge neral, the lift-off process is beneficial for semiconductor quantum dot spe ctroscopy, since the original surface condition of the substrate is not alt ered or destroyed as it may be in a conventional dry or wet etching process es to form apertures in a subtractive process. With an optimum combination of process parameters, such as higher pre- and postexposure bake temperatur es for longer times, longer developing time and with optimal mixtures of de velopers, high aspect ratio resist posts were obtained. Using 20 kV single dot e-beam exposure, a reentrant profile can be obtained directly. While th is profile is not obtained with 50 kV single dot e-beam exposure, a higher aspect ratio (similar to 7:1) and sub-100 nm diam resist posts are possible . High vertical sidewall 100 nm diam resist posts are obtained using 50 kV area e-beam exposures. Taking advantage of these characteristics: high aspe ct ratio, high vertical resist sidewall, and resist undercut at the bottom of post, sub-100 nm diam apertures in 100 nm thick metallic films are obtai ned by evaporation of metal on the sample and dissolving the resist post in solvent. For sub-100 nm apertures, a significant improvement in aperture e dge smoothness was achieved by applying an oxygen plasma. (C) 1998 American Vacuum Society. [S0734-211X(98)06606-2].