Microfabrication techniques are successfully used for semiconducting materials, while they are limited for the application to magnetic materials. For the magnetic materials, useful RIE (reactive‐ion‐etching) process that is essential for high‐resolution microlithography has not yet been successful. In this work, RIE method useful for permalloy (80%Ni‐4.5%Mo‐Fe) has been newly constructed. High‐resolution electron‐beam writing was followed by the RIE process, leading to 250 nm line and space patterns in the permalloy film with 10 nm accuracy. In order to achieve a high‐resolution electron‐beam writing, amorphous carbon film was use between the resist layer and SiO2 film overlaid on the permalloy film. There are four levels in the process. Most critical step in the fabrication of magnetic material is RIE process using a rf discharged plasma of NH3‐CO mixed gas. Maximum etching rate of 35 nm/min and highly anisotropic etching for the permalloy was obtained at the composition of 50 mol % NH3‐CO at the pressure of 2.4×10−3 Torr. The etching selectivity ratio of permalloy to SiO2 employed as a mask was about 10. By this method, nanostructures of permalloy with highly anisotropic profile were fabricated. This method shows prominent features still for Co‐Cr alloy films.

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