Development of Wafer-Level Wet Atomic Layer Etching Process Platform for Cu Surface Topography Control in Hybrid Bonding Applications

As for the next generation device frontiers with 3D-stacked architecture involving copper-to-copper hybrid bonding (or hybrid copper bonding), process innovation is inevitable to fulfill such kind of sophisticated technology. Among variety of different process and equipment-level challenges for seamless hybrid bonding, surface topography control of $\mathbf{C u}$ /dielectric is considered to be one of the most important aspect to achieve and in this regard, CMP process has been a key player in providing uniform copper $(\text{Cu})$ recess across device wafers prior to bonding. With continued scaling down of Cu pads and pitch, however, CMP process is facing tighter margin in target specification, which requires more precise, sub-nanometer controllability of Cu recess profile to guarantee successful 3D integration. In our previous work, we introduced a novel approach that offers exceptional Cu recess controllability through a cyclical treatment of wet chemicals and explored the potential of this innovative process as a new measure to compensate and mitigate the limitation of CMP process in hybrid bonding implementation. Here, we expand the capability of this so-called wet atomic layer etching (ALE) process to a 300 mm wafer-level platform and report results of targeting Cu recess within a nanometer range. The versatility of wet ALE solution is discussed based on process and hardware evaluations that were carried out on a hybrid bonding test vehicle with Cu pad size and pitch dimension below $0.4 / 0.8 \mu ~\mathrm{m}$. Specifically, chemical dispense related terms were tuned to probe whether the initial protrusion or recess profile can be complemented on-the-fly to concede inwafer uniformity. The experimental findings from this work suggests advancement of wet ALE process and its applicability to enable precise, $\sim 0.5 ~\text{nm} /$ cycle wafer-level controllability of Cu surface topography.