50 nm Overlay Accuracy for Wafer-to-wafer Bonding by High-precision Alignment Technologies

We have developed a wafer-to-wafer bonder for high-precision fusion/hybrid bonding and demonstrated an approximately 50 nm bonding overlay accuracy in continuous bonding of 12 sets of wafers. In this report, we evaluated the results in more detail and showed that the bonding deviation was 40 nm or less for 95% of the measurement points and approximately less than 30 nm for 80% of the measurement points. We also analyzed the bonding results and additional data from another aspect. As a result, we identified the importance of the following three technical factors with respect to the reproducibility of shift-rotation components: multipoint measurement for wafer bonding, stage control accuracy when two wafers first come into contact, and the effect of distortion due to upper wafer protrusion on the formation of the bonding wave initiation point. We have achieved the above high-precision bonding results by optimizing these technical factors for our original technologies. These technologies are essential for further improvement of bonding overlay accuracy in the future. Furthermore, we evaluated the distortion correction technology, which is another indispensable component for improving the bonding overlay accuracy. As a result, we analytically confirmed the fine correction effect on wafers with a saddle-shaped warpage of ±250 µm using our systems. As a prospect for future bonding overlay accuracy, we also analytically confirmed the high possibility of bonding overlay with| Ave|+3σ of 25 nm or less by improving the reproducibility for each component. These results show the possibility of further scaling the wafer-to-wafer bonding pitch, and we believe that these technologies will greatly contribute to the development of future three-dimensional integrated circuits.