Application of resolution enhancement techniques in thin film head processing

Abstract

As thin film head (TFH) processing advances with magneto resistive (MR) and giant magneto resistive (GMR) designs, thephotolithographic requirements for the write portion of the device grow increasingly challenging. Specifically, the resolutionof submicron isolated features is required in thick photoresist films; resulting in aspect ratios of nearly 10 to 1. To satisfy theimaging requirements of critical read and write-layers, the use of i-line reduction lithography tools with variable numericalaperture (NA) and partial coherence (a) are necessary.This study examines the influence of NA, a, and reticle bias on critical features in typical TFH write-layer processes.Optimal reticle bias was estimated through simulation and confirmed experimentally. Combinations of NA and wereinvestigated for their impact on minimum feature size, process latitude, and sidewall angle for multiple resist thicknesses.Process latitude was quantified for each illumination condition over a range of focus and exposure conditions with the use ofa low-voltage, automated TFH CD-SEM. A focused ion beam (FIB) tool and SEM are used to examine wall angles at eachofthe illumination conditions.Keywords: Thin film heads, process latitude, exposure optimization, thick photoresist.