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30 December 2003 Bi/In thermal resist for both Si anisotropic wet etching and Si/SiO2 plasma etching
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Proceedings Volume 5342, Micromachining and Microfabrication Process Technology IX; (2003)
Event: Micromachining and Microfabrication, 2004, San Jose, California, United States
Bi/In thermal resist is a bilayer structure of Bi over In films which can be exposed by laser with a wide range of wavelengths and can be developed by diluted RCA2 solutions. Current research shows bimetallic resist can work as etch masking layer for both dry plasma etching and wet anisotropic etching. It can act as both patterning and masking layers for Si and SiO2 with plasma “dry” etch using CF4/CHF3. The etching condition is CF4 flow rate 50 sccm, pressure 150 mTorr, and RF power 100 - 600W. The profile of etched structures can be tuned by adding CHF3 and other gases such as Ar, and by changing the CF4/CHF3 ratio. Depending on the fluorocarbon plasma etching recipe the etch rate of laser exposed Bi/In can be as low as 0.1 nm/min, 500 times lower than organic photoresists. O2 plasma ashing has little etching effect on exposed Bi/In. Bi/In also creates etch masking layers for alkaline-based (KOH, TMAH and EDP) “wet” anisotropic bulk Si etch without the need of SiO2 masking steps. The laser exposed Bi/In etches two times more slowly than SiO2. Experiment result shows that single metal Indium film exhibits thermal resist characteristics but at twice the exposure levels. It can be developed in diluted RCA2 solution and used as an etch mask layer for Si anisotropic etch. X-ray diffraction analysis shows that laser exposure causes both Bi and In single film to oxidize. In film may become amorphous when exposed to high laser power.
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Glenn H. Chapman, Yuqiang Tu, and Jun Peng "Bi/In thermal resist for both Si anisotropic wet etching and Si/SiO2 plasma etching", Proc. SPIE 5342, Micromachining and Microfabrication Process Technology IX, (30 December 2003);

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