Nanolithography by Electron Beam Resist-trimming Technique
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Nanolithography by Electron Beam Resist-trimming Technique Tatsuro Maeda, Kenichi Ishii, Eiichi Suzuki, Hiroshi Hiroshima, Tsutomu Iida*, Yoshihumi Takanashi*, Parhat Ahmet**, Toyohiro Chikyow**, and Hirohisa Taguchi*, Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305-8568, Japan *Faculty of Industrial Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda, Chiba 278-8510, Japan **COMET-NIRIM, National Institute for Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan (PDLO [email protected]
ABSTRACT We have investigated a resist-trimming process for SAL601 chemically amplified negative electron beam resist. Ultra-fine SAL601 resist patterns with a width of 16nm were obtained by an isotropic trimming process in oxygen plasma. This pattern resolution in SAL601 could not be obtained through direct electron beam lithography alone. Using the trimmed electron beam resists, we have successfully fabricated ultra-fine poly-silicon patterns of less than 20nm width. We applied this nanolithography technique to fabricating an ultra-small metal-oxide-semiconductor field-effect-transistor (MOSFET) and revealed that this trimming process is a useful method for nanometer-scale silicon device fabrication. INTRODUCTION
Nanometer-scale fabrication technology is one of the most important issues to realize various ultra-small electron devices. The resolution limit of device fabrication by means of electron beam lithography has now approached 10nm. As far as electron beam lithography with a positive resist is concerned, ultra-fine patterns have already been realized in inorganic resists (SiO2 and LiF) at 5nm, and in organic resists (PMMA) at 6nm [1,2,3]. In contrast, a fine pattern formation technology using a negative resist is far from an advanced level. Chemically amplified negative resists (CARs) are technologically important because they have high sensitivity, high resolution, and high durability to the subsequent semiconductor etching process. In these types of resists, the SAL601 (Shipley Co.) has the highest resolution of sub-50nm reported so far [4,5]. For such a negative resist technology, the characteristics of organic resists become critically important. Systematic studies on the chemical properties of organic negative resists have revealed that the resists with smaller molecular weight tend to have finer resolution [3]. From this viewpoint, the calixarene resist with a molecular weight of 950, and recently the α-methylstyrene resist with a molecular weight of 650 have been developed for ultra fine electron beam lithography with a resolution down to 10nm [6,7]. However, these high-resolution negative resists show low sensitivity, so that extremely long exposure time is required. Also, plasma-etching durability is low compared to CARs, and this is a serious problem for the subsequent etching process. To obtain finer resist patterns than those defined by electron beam lithography alone, an isotropic photoresist-trimming process has already been used to fabricate ultra
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