Journal
MATERIALS & DESIGN
Volume 210, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.matdes.2021.110052
Keywords
High-resolution X-ray diffraction; X-ray micro computed-tomography; Wafer bonding, crystal microstructure degradation; Stress in crystals
Categories
Funding
- Swiss Innosuisse project ATOM Impulse atom assembly technology for MEMS [37572.1 IP-ENG]
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The study evaluates an innovative silicon-to-sapphire wafer bonding process using a combined analytical approach of HRXRD and X-ray micro-CT. Large cracks in both crystals related to high-stress release at the interface were identified, along with smaller cracks and defects affecting silicon crystallinity due to multi-domain microstructure associated with strain and tilt. This unique approach combines micro CT with HRXRD for a holistic evaluation of silicon-to-sapphire wafer-bonding processes.
Devices such as sensors, actuators, or micro-electromechanical systems (MEMS) are obtained by a variety of microfabrication processes. Many of these processes influence the material systems by the introduction of strain and defects, which may affect the final device's performance and reliability. Indeed, controlling materials' status during the microfabrication is fundamental for the process optimization itself and for guaranteeing the highest devices performances during their lifetime. In this work, a conjoint analytical approach between high-resolution X-ray diffraction (HRXRD) and X-ray micro-computed tomography (CT) evaluates an innovative silicon-to-sapphire wafer bonding process. Large cracks 30-60 mm thick were identified in both crystals by micro-CT and related to the interfacial high-stress release. In parallel, a multi-domain microstructure associated with strain and tilt affect the silicon crystallinity due to smaller cracks and defects which originate at the bonding interface and travel to the outer part of the crystal. The effectiveness of the bonding is also assessed by our approach and further enforced by means of SEM observation of the sample cross-section. Here, a unique approach by combining X-ray micro CT with HRXRD for a holistic evaluation of silicon-to-sapphire wafer-bonding processes and correlate the micrometer scale and volumetric defect detection (voids and cracks) with atomic-level strain and defect analysis is presented. (C) 2021 The Authors. Published by Elsevier Ltd.
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