High-aspect-ratio x-ray lithography for magnetic head fabrication

Abstract

The development of the future-generation magnetic recording heads is based on availability of high resolution and high-aspect ratio lithography. A key step in the magnetic head fabrication process is the formation of high-aspect ratio trenches in photoresist that are subsequently used as a plating mask for the magnetic read-write heads. Currently, 1.2 to 1.5pm wide and lOjzm tall trenches in the resist are formed using optical lithography. In the near future, more than 6pm tall resist patterns with trenches of O.5pm or smaller will be required. A study of using X-ray lithography to generate patterns suitable for future-generation magnetic recording heads was undertaken at the Center for X-Ray Lithography at UW-Madison. It was successfully demonstrated that O.8jim trenches in 15tm thick resist and O.4,am trenches in 6pm thick resist can be formed. The main steps in the fabrication of the high-aspect ratio resist patterns included a) production of an initial (master) mask using e-beam lithography, b) high-contrast replicated (final) X-ray mask manufacturing using X-ray replication process, and c) actual patterning of thick PMMA resist using the final mask. Both X-ray masks were formed on a 2pm thick silicon-nitride membranes as mask carrier. APEX-E resist O.5pm thick was used for e-beam writing, and 2pm thick PMMA was utilized for the replicated mask. The absorber was electroplated gold: O.4pm thick for the master and 1.5pm thick for the final mask. Details are given for 6pm and l5pm thick crack-free PMMA resist formation and characterization, exposure and development conditions.