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High Selectivity Laser-Assisted Chemical Etching for Glass Interposer Application
Keywords: Laser-assisted, High Selectivity, Glass interposer
The glass is an abundant material with very good electrical isolation that is suitable for the substrate of an interposer for 3DIC integration to increase package density, reduce routing length for signal propagation, and increase the functionality and clock rate of a system. In this work, we demonstrate through-glass via for glass interposer by laser-assisted chemical etching exhibiting extremely high selectivity. These via holes were identified by direct laser scanning. After post-annealing, the laser-illuminated region becomes crystallized. The crystalline region of the glass exhibits higher etching-rate in the diluted hydro-fluoride acid (HF:H2O=1:10) than amorphous region. Ultra-violet (355 nm) pulse laser was used in this experiment. With a 6 J/cm2 laser energy, high-density via holes with 50m in diameter was fabricated in a 600m thick glass. The pitch of via holes is approximately 100m. The aspect ratio was around 12. Comparing the thickness of glass before and after chemical etching, the laser-illuminated region exhibits approximately 40m/min etching-rate in diluted HF. Meanwhile, the etching-rate for of the non-laser-illuminated glass was approximately 1m/min. As a consequence, the selectivity is approximately 40. In comparison, direct laser drilled through-glass via holes were also fabricated. Approximately 40 times higher energy (12 J/cm2 with exposure 20 times) was required to make a via hole with 50m in diameter on a 600μm thick glass. In addition, glass is not a good thermal conductor, resulting micro-cracks were found on the glass due to local heating by persistent laser drilling. According to our results, the laser-assisted chemical etching is an easy, reliable technique and is able to scale-up technology to make a high-density through-glass via holes (diameter to pitch is 1:2) for the application of glass interposer. The sub-micron through-glass via hole was possible implemented by this technology by laser illumination on pre-patterned glass.
Zingway Pei, Associate Professor
1. Graduate Institute of Optoelectronic Engineering, National Chung Hsing University, 2. Electronics and Optoelectronics Research Laboratories (EOL), Industrial Technology Research Institute (ITRI)
Taichung, Taiwan
Republic of China

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