Challenges of implementing 193-nm lithography in printing sub-70nm line patterns for thin film heads

Abstract

The rapid increase in the areal density of hard drives has demanded a parallel improvement in component technology. In particular, the development of new thin film heads (TFH) requires the constant reduction of read head track widths. State-of-the-art lithography techniques have been invoked to keep pace with the need for smaller read-head patterning. The critical feature in the read head is the sensor width, MRW. The aggressive roadmap for the thin film head industry makes it essential to print 70nm isolated lines or below for the next generation. KrF lithography, extensively used in the current node, is inadequate to produce read heads with 70nm and narrower isolated lines. Optical lithography will need to transition to 193nm for products of the future generation. This paper reviews the challenges posed by the transition from KrF to ArF lithography in thin-film head processes. Using ArF scanners and binary masks, 100nm isolated lines can be printed with 8nm across-field CD variation. Alternating phase shifting masks (AltPSM) are utilized to further enhance the resolution. Metal deposition into lithographically defined stencils increases the difficulty of stripping photo resist. To facilitate the resist stripping, a release layer like PMGI is often applied beneath the photo resist. However, the resolution improvement from ArF lithography makes it difficult to control the even narrower release layers. In this paper we demonstrate an alternative approach, a bridge structure, to lift off photo resist. The results show the success of constructing 4um-long bridges with sub-100nm track width. Therefore this can be a promising alternative means of producing MRW.