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Although semiconductor industry ramps the products with 90 nm much quicker than anticipated [1], magnetic recording head manufacturers still have difficulties in producing sub-100 nm read/write trackwidth. Patterning for high-aspectratio writer requires much higher depth of focus (DOF) than most advanced optical lithography, including immersion technique developed recently [2]. Self-aligning reader with its stabilized bias requires a bi-layer lift-off structure where the underlayer is narrower than the top image layer. As the reader's trackwidth is below 100nm, the underlayer becomes very difficult to control. Among available approaches, e-beam lithography remains the most promising one to overcome the challenge of progressive miniaturization. In this communication, the authors discussed several approaches using ebeam lithography to achieve sub-100 nm read/write trackwidth. Our studies indicated the suspended resist bridge design can not only widen the process window for lift-off process but also makes 65 nm trackwidth feasible to manufacture. Necked dog-bone structure seems to be the best design in this application due to less proximity effects from adjacent structures and minimum blockages for ion beam etching. The trackwidth smaller than 65 nm can be fabricated via the combination of e-beam lithography with auxiliary slimming and/or trimming. However, deposit overspray through undercut becomes dominated in such a small dimension. To minimize the overspray, the effects of underlayer thickness need to be further studied.

Lift-off process is widely used to pattern small-dimension features for microelectronics. To do lift-off process, one needs to have bi-layer photoresist with desired undercut. As the critical dimension (CD) of devices is decreased, the process becomes very difficult to achieve CD and the degree of undercut simultaneously. Conventional TMAH development process alone becomes no longer feasible. Especially, due to the demand to increasingly reduce CD, the image layer’s CD and bottom layer’s undercut becomes too tight to control. In this presentation, we proposed a wet and dry process simultaneously to optimize CD and undercut. This approach is to form a photoresist feature with a larger CD using conventional wet development process. It is followed by dry development to produce the desired small CD and undercut. The critical process parameters in both steps were investigated using NEB22A2 and PMGI photoresists. The present method can also be used to produce nano-monolayer photoresist features.

Conventional lift-off process uses dual-layer resists for transferring image into the substrate (top layer) and releasing the deposit (bottom layer). However, as the critical dimension of top layer approaches sub-100 nm, the undercut of bottom layer for subsequent lift-off process becomes very difficult to control. An alternative approach is to use single-layer resist to do lift-off. Such a process requires resist patterns with a negative-slope sidewall angle, which is not easily achieved by the optical lithographic tools. In this communication, we presented a lift-off method using a tilted electron beam and further development to produce sub-100 nm features with a negative-slope sidewall angle. This process was demonstrated in a negative-tone chemically amplified resist (NEB22A2) by using an exposure electron-beam system (Hitachi-900D). The computations, based on Monte Carlo simulations, were found to be in good agreement with the experimental results. Two extensive applications for recording heads were also presented.

In this communication, we presented a novel approach to reduce critical dimension of resist features. The proposed method involves two process steps: resist pattern formation and critical dimension reduction. This concept was demonstrated to produce sub-100 nm resist features using negative-tone chemically amplified resist, NEB22A2 and Hitachi-900D electron beam lithography system. Experimental results indicate that the degree of critical dimension reduction can be controlled by the dose of flood electron-beam exposure and second wet developer strength. The theoretical results, based on Monte Carlo simulations, were found to be in qualitatively agreement with our experimental observations.