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Fabrication of Through via Holes in Ultra-Thin Fused Silica Wafers for Microwave and Millimeter-Wave Applications

School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, NSW 2052, Australia
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Micromachines 2018, 9(3), 138; https://doi.org/10.3390/mi9030138
Received: 14 February 2018 / Revised: 8 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
Through via holes in fused silica are a key infrastructure element of microwave and millimeter-wave circuits and 3D integration. In this work, etching through via holes in ultra-thin fused silica wafers using deep reactive-ion etching (DRIE) and laser ablation was developed and analyzed. The experimental setup and process parameters for both methods are presented and compared. For DRIE, three types of mask materials including KMPR 1035 (Nippon Kayaku, Tokyo, Japan) photoresist, amorphous silicon and chromium—with their corresponding optimized processing recipes—were tested, aiming at etching through a 100 μm fused silica wafer. From the experiments, we concluded that using chromium as the masking material is the best choice when using DRIE. However, we found that the laser ablation method with a laser pulse fluence of 2.89 J/cm2 and a pulse overlap of 91% has advantages over DRIE. The laser ablation method has a simpler process complexity, while offering a fair etching result. In particular, the sidewall profile angle is measured to be 75° to the bottom surface of the wafer, which is ideal for the subsequent metallization process. As a demonstration, a two-inch wafer with 624 via holes was processed using both technologies, and the laser ablation method showed better efficiency compared to DRIE. View Full-Text
Keywords: microwave and millimeter-wave; through via hole; fused silica; DRIE; laser ablation; etch rate microwave and millimeter-wave; through via hole; fused silica; DRIE; laser ablation; etch rate
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Li, X.; Chan, K.Y.; Ramer, R. Fabrication of Through via Holes in Ultra-Thin Fused Silica Wafers for Microwave and Millimeter-Wave Applications. Micromachines 2018, 9, 138.

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