Characterization of OPC masks for thin-film head pole trimming applications

Abstract

The storage space of hard disk drives more than doubles every 18 months. In order to maintain this growth rate, thin film head (TFH) manufacturers continue to seek new technologies to increase the areal density on the magnetic media. The trimming of the track at the rowbar level known as 'pole trimming' has proven itself to be very effective at increasing the number of tracks per inch (TPI) during the inductive head generation. However, the transition to magneto-resistive (MR) head technologies with ever smaller form factors has continued to push the trackwidth (TW) requirements of the industry. Optical proximity correction (OPC) enhanced masks have been used in the semiconductor industry for controlling the shape of contacts and eliminating line shortening effects for submicron features. The TFH industry is facing a similar challenge as TWs dip below 1 micrometer. In an attempt to transition the pole trimming process technology from inductive to MR heads, the issue of magnetic performance versus pattern fidelity of the feature becomes critical. OPC masks can be used to minimize the corner rounding effects of trimmed shared magnetic poles, which are ultimately responsible for the track width. This paper evaluates OPC mask technology on rowbar level pole trimming using a 1X stepper to identify the extendibility of minimum TWs for the MR head generation. Various combinations of serifs were experimentally evaluated at different track widths. Multiple photoresists and photoresist thicknesses were selected to represent the range of processes used in the industry. The experimental results were then compared with photoresist simulation studies of the same OPC reticle features. The validation of the simulation results allowed a wider range of conditions to be studied. The results show that OPC is an effective technique for enhancing pole trimming and extending the areal density of modern head designs.