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29 June 2001 Prototype laser-activated bimetallic thermal resist for microfabrication
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The Thermal Resist Enhanced Optical Lithography (TREOL) process models an optical system to double device resolution by exploiting non-reciprocal laser activated processes. A possible prototype thermal resist consists of stacked bismuth on indium layers sputter deposited on a glass/quartz substrate with thickness ratios matching the eutectic alloy (Bi 53%). Laser radiation locally melts the metals which alloy upon cooling. BiIn resist is relatively wavelength insensitive because its UV optical characteristics vary modestly. Reflection and energy absorption/cc calculations indicate the best arrangement is a 30-45-nm total thickness bilayer with bismuth on indium. Exposing the highly absorbing BiIn with CW argon (514/488 nm) or 4-ns Nd:YAG pulses at 533 nm (40 mJ/cm2 for 300-nm thick) and 266 nm transforms the resist to a weakly absorbing alloy with a visually identifiable pattern. 30-nm thick converted film transmission changes from 1.0OD to 0.35OD (830-350 nm) until a 350-nm absorption edge. Profilometry and SEM showed no signs of ablation or oxide growth in exposed areas. The resist was developed with HNO3:CH3COOH:H2O etch, preferentially removing unexposed areas, leaving written patterns of alloyed lines seen both in profilometry and SEM images. Thus BiIn forms a complete thermal alloying resist with selectively etched exposed patterns that can be stripped in an HCl:H2O2:H2O bath.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Marinko V. Sarunic, Glenn H. Chapman, and Richard Yuqiang Tu "Prototype laser-activated bimetallic thermal resist for microfabrication", Proc. SPIE 4274, Laser Applications in Microelectronic and Optoelectronic Manufacturing VI, (29 June 2001);

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