Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substr
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1052-DD06-26
Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substrates Chiemi Ishiyama, Akinobu Shibata, Masato Sone, and Yakichi Higo Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 R2-18 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT Adhesive bend testing of micro-sized photoresist components has been performed to clarify the effects of supercritical CO2 (ScCO2) treatment. Multiple microsized cylindrical specimens were fabricated on a silicon substrate using epoxy-type photoresist. The specimens were ScCO2 treated at a temperature of 323K at a pressure of 15MPa for 30 min, and then decompressed to atmospheric pressure at two different rates. Double refraction appeared in the SU-8 specimens near the interface between the SU-8 specimens and the substrate after ScCO2 treatment. The adhesive bend strength of ScCO2 treated specimens based on the slow decompression process is approximately 60% higher than that of non- ScCO2 treated specimens; however, the strength of the microsized photoresist was slightly degraded by ScCO2 treatment with the quick decompression process. All the results suggest that ScCO2 treatment can improve the adhesive strength between microsized photoresist components and a silicon substrate with control of the decompression process. INTRODUCTION In the last few decades, microfabrication for micro-electro mechanical system (MEMS) devices has made remarkable progress based on photolithography, which utilizes a fine photoresist pattern as a mask during etching process or as a mold for sputtering or plating. Recently, micro-sized elements for MEMS devices have become more complicated and now are often based on three dimensional shapes, therefore, it is desirable that the photoresist pattern is thicker with a high aspect ratio for MEMS devices. However it is difficult to completely clean the micro-sized photoresist patterns with complicated shapes and high aspect ratios using wet cleaning techniques, because the surface tension between the cleaning solvent and micro-sized photoresist patterns interferes with circulation of the fresh solvent throughout all the surfaces of the micro-sized patterns. Recently, supercritical carbon dioxide (ScCO2) cleaning is being explored as an alternative to wet cleaning for sub-micron patterning [1]. ScCO2 has near zero surface tension, high diffusivity and high solubility, thus, it can clean fine photoresist patterns completely. On the other hand, amorphous polymers absorb ScCO2 and swell [2], which causes plasticization of these materials [3]. It has been suggested that the adhesive strength between micro-sized photoresist patterns and the Si substrate would be affected by the ScCO2 treatment. However, there are few studies about the effects of ScCO2 on the adhesive properties. In this study, adhesive strength between microsized photoresist patterns and silicon substrates is quantitatively evaluated to clarify the effects of ScCO2 treatment. Micro-sized cylindrical
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