Low Temperature Wafer Bonding for 3D Applications

Abstract

Due to the high process temperature required for fusion bonding (e.g. ~1000°C) this process was not attractive for 3D applications. In the recent years low temperature fusion bonding processes were developed for addressing low temperature applications. A low temperature CMOS compatible fusion bonding process based on plasma activation of the substrate surfaces prior bonding was developed. The low temperature fusion bonding process was used in combination with standard thin wafer manufacturing processes in order to enable and demonstrate thin layer wafer bonding with subsequent multi-layer stacking capability. The process is compatible with the high cleanliness levels required by CMOS technology and can be used for various application scenarios involving through-silicon vias (TSV) technology.

Monolithic Thin Wafer Stacking Using Low Temperture Direct Bonding

“…No metal interconnects were fabricated in this study, as this will be part of future work. The results presented here are a continuation of previously reported results in which 3wafers stacks were fabricated using 200 mm wafers: one full thickness (725 µm) and two ~20 µm thin Si wafers [1]. The focus of this study was to evaluate the ultra-thin wafer (10 µm) fabrication using temporary bonding followed by subsequent layer transfer using low temperature fusion bonding on 300 mm production sized wafers.…”

“…The most significant difference between the two debonding processes is that for the LowTemp TM debonding the separation of the wafers is performed at room temperature, ECS Transactions, 64 (5) 95-101 (2014) whereas the debonding using the slide-off process is performed at elevated temperatures (around 180°C, depending on the temporary bonding adhesive type) [3].Detailed process description of the individual processes can be found elsewhere [1].…”

Delamination Root Cause in Temporary Bonding

“…One of the key points for an entire 3D integration success is being able to handle the thin wafer during backside processing reliably. Temporary bonding has emerged as one of the answers [3][4]. However, some challenges still need to be overcome in order to fully control and understand this technique.…”