Fabrication of c-Si Pillars on Glass Substrates for Terahertz Dielectric Metasurfaces Using Glass-Silicon Direct Bonding

This study employs a low thermal budget glass-to-silicon direct bonding process without interlayers to fabricate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$200\mu \mathrm{m}$</tex> thick crystalline silicon (c-Si) pillars processed on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300\text{mm}$</tex> glass substrates. The process demonstrated robust bonding integrity, with no chip-off even after rigorous backgrinding procedures. Comprehensive investigations were conducted on the selection of glass substrates, the impact of cleaning processes on the bonding interface, and the optimization of these cleaning protocols. Additionally, lithography and etching processes were optimized on blank silicon wafers prior to their application on glass-bonded wafers. Challenges associated with handling glass on electrostatic chucks (ESC) were also addressed. Following these optimizations, a detailed process flow was developed for fabricating thick silicon pillars with aspect ratio ranging of 1:2. Surface and interface analyses were performed using confocal scanning acoustic microscopy, optical/laser profilometry, and X-SEM inspections. This fabrication flow shows significant potential in the fields of advanced packaging, optoelectronics, microfluidics, MEMS, and terahertz (THz) technologies.