Precision wafer bonding process for future cost-effective 3DICs

A high-precision wafer-to-wafer (W2W) bonding system for three-dimensional integrated circuits (3DICs) fabrication adopting a new precision alignment methodology is proposed. In studying W2W device yield, the authors split the stacking W2W yield formula to better understand the systematic versus random components, and propose that miniaturization yield and wafer stacking yield should be considered separately. Experimental results show that the W2W alignment capability is 250 nm or better, with similar overlay accuracy (|mean| + 3σ) for high-throughput Cu-Cu permanent bonding. These capabilities are key enablers for the future of cost-effective 3DIC manufacturing.