Ion Beam Lithography for Nano-scale Pattern Features
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1020-GG02-03
Ion Beam Lithography for Nano-scale Pattern Features John E.E. Baglin, Andrew J. Kellock, and Jane E. Frommer IBM Almaden Research Center, 650 Harry Road, San Jose, CA, 95120 ABSTRACT With the expected availability of new tools for creating patterned ion beams containing few-nanometer sized features, it is important to examine the fidelity of registering such patterns in a receiving medium, such as the photoresist layer in a lithographic fabrication process. In this paper, we report experiments exploring the characteristics of ion beam patterning of polymethylmethacrylate (PMMA) and polystyrene (PS) coatings on silicon substrates, with respect to their response as positive / negative resists to patterned low-energy H+, He+ and Ne+ beams. We examine by atomic force microscopy (AFM) the feature profiles thus created after solvent development of the polymer layers, and we examine the dependence of the polymer response upon ion species and fluence. Reasonable feature profiles are readily obtained in fluence ranges around 1013 ions/cm2. Proximity effects are shown to be negligible except after over-exposure at very high ion fluences. Granularity within the final pattern features is shown to be a potential concern for high energy, light ion irradiations. Optimization of feature geometries is clearly possible by appropriate selection of ion species, energy and fluence to suit the receiving medium.
INTRODUCTION In view of their freedom from interference patterns, their minimal proximity effects in complex pattern lithography, and their adaptability for parallel processing, ion beams are expected to reach beyond the current manufacturing technologies based on e-beams or UV lithography. Achieving feature resolution of only a few nanometers, and offering highly flexible and reliable process throughput with long range pattern coherence, ion beams will enable fulfillment of Mooreís Law for semiconductor systems, and similar advances for high density magnetic storage media. Prototype projection ion beam tools, designed for parallel transfer of a complete large-area pattern with demagnification factors between 4 and 20, have demonstrated the robustness, precision, and throughput needed to make this approach economically attractive [1-4]. Programmable masks and higher demagnification factors are expected to further enhance the scope of applications in the future. It is therefore timely to explore the optimization, and physical limits, of spatial resolution in registering an ion beam pattern in materials suitable for the role of lithographic resists. We report an initial experimental study of the sharpness of pattern registration in thin films of polymethylmethacrylate (PMMA) or polystyrene (PS) exposed to low energy ions patterned by means of a contact stencil mask.
EXPERIMENT Polymer resist coatings In these experiments, we compared the performance characteristics for PMMA and PS. The linear PMMA polymer structure is readily broken by chain scission events caused by the passage of energetic ions, leading to enhanc
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