Sub-100 nm pattern formation using a novel lithography with SiNx resist by focused ion beam exposure and dry-etching development

A novel lithography applicable to in situ processing is proposed, where plasma-chemical-vapor-deposited (PCVD) SiNx is used as a resist, exposure is by Ga focused ion beam (Ga-FIB) implantation, and CF4 dry etching is used for development. The Ga-implanted SiNx film acts as a negative resist for CF4 dry-etching development when the ion dose exceeds 1016 cm−2. The imaging contrast appears to be 4.0 when the acceleration voltage in the FIB exposure is 40 kV and chemical dry-etching development is employed. Very fine resist patterns of 50 nm are obtained using the finest beam available with our FIB system in combination with anisotropic reactive ion etching development. The substrate damage due to FIB exposure is not significant thanks to the presence of the SiNx resist. GaAs substrates are successfully dry-etched with deep and anisotropic profiles using SiNx masks fabricated by this lithography method.