Integration Solution for Thin D2w Hybrid Bonding for Yield and Reliability

Hybrid bonding is a critical technology that enables high-density interconnects. It involves placing a die on a substrate to initiate a Van der Waals dielectric-dielectric bond, followed by a post-bond anneal process. This annealing process enhances the dielectric bonds, transforming them into covalent bonds.

Additionally, it allows embedded copper (Cu) to diffuse across the bonding interface, forming electrical connectivity. One of the challenges associated with hybrid bonding is moisture imbibition. This issue has been observed in wafer-to-wafer (W2W) direct bonding and can occur within less than four hours under extreme conditions [1].

In die-to-wafer (D2W) hybrid bonding, where more die boundaries are exposed to wet processes and longer waiting times are involved (such as in direct multi-stack bonding in High Bandwidth Memory applications or when accumulating wafers for post-bond annealing in a batch chamber), the problem of moisture imbibition is expected to become more severe. Water imbibition can weaken the bond interface, leading to the formation of voids and an increase in the resistance of Cu bonding pads. To assess and mitigate the degradation of the D2W bond interface, aging tests such as unbiased Highly Accelerated Stress Test (uHAST) [2] or other moisture-related tests like the JEDEC standard Moisture Sensitivity Test (MST) [3] test can be employed.

These tests help to evaluate the impact of moisture on the bond interface. The degradation is expected to be most prominent near the bonded die edge or corner, as these regions are particularly susceptible to such degradation. By understanding and addressing the challenges associated with moisture imbibition in D2W hybrid bonding, it is possible to develop strategies to enhance the reliability and performance of high-density interconnects.

This report presents a solution for the integration process of thin dies with a die thickness of 50 um using D2W bonding. The proposed solution successfully passed both the as-bonded state and reliability performance tests, including electrical test yield and aggregated aging stress tests. The reliability tests included MSL-1 (85° C-85 % RHfor 168 hours) and thermal cycling (TC) of 1000 cycles\left(-40° C\right.to\left.125° C\right).