Demonstration of 50 nm Overlay Accuracy for Wafer-to-Wafer Bonding and Further Improvement Study

We have developed next-generation wafer-to-wafer (W2W) bonder suitable for mass production of fusion/hybrid bonding. To realize high-precision bonding overlay accuracy, this bonder applies high-precision alignment technologies such as enhanced wafer global alignment (EGA) and stage control, which were specially optimized and developed for bonder. We have developed these technologies on the basis of our long experience with lithography tools. We have also developed a new correction method for bonding distortion, which is a peculiar issue of bonding overlay in fusion/hybrid bonding. By these new technologies, we have consistently obtained the world's highest bonding overlay accuracy of 50 nm and less than 30nm of residual components with continuous bonding of 12 sets of fusion TEG wafers. The number of measurement points of each wafer is 397 within a radius of 142 mm. Moreover, we also confirmed the application of this method to a hybrid bonding wafer with an actual device, which is more susceptible to bonding distortion, and obtained a bonding overlay accuracy of 59 nm. In principle, this correction method is also effective for various warped wafers, and we believe that it can be applied to the mass production of wafers. To further improve the accuracy, we also analyzed and studied a new method to realize a 25 nm overlay accuracy for W2W boding. These results show the possibility of further scaling of the W2W bonding pitch, and we believe that this technology will greatly contribute to improving the performance of future three-dimensional integrated circuits.