As thin film head (TFH) processing advances with magneto resistive (MR) and giant magneto resistive (GMR) designs, the photolithographic requirements for the write portion of the device grow increasingly challenging. Specifically, the resolution of submicron isolated features is required in thick photoresist films; resulting in aspect ratios of nearly 10 to 1. To satisfy the imaging requirements of critical read and write-layers, the use of i-line reduction lithography tools with variable numerical aperture (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 were investigated 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 of a low-voltage, automated TFH CD-SEM. A focused ion beam (FIB) tool and SEM are used to examine wall angles at each ofthe illumination conditions.