Achieving Sub-nm Copper Recess Controllability for Advanced 3D Integration: An Experimental and Atomic-scale Simulation Study on Wet Atomic Layer Etching Process

For the next generation memory devices such as 3D-NAND involving copper-to-copper (C2C) hybrid bonding process, chemical mechanical planarization (CMP) process is a vital step to provide uniform copper (Cu) recess across device wafers prior to bonding. Despite the importance of CMP process for a successful 3D integration, continued scaling down of Cu pads and pitch within the devices requires more precise, sub-nanometer controllability of the recess topology. Here, we report a novel approach to fulfill such aspects through a cyclical treatment of wet chemicals to etch the Cu surface layer by layer. This wet atomic layer etching (ALE) process demonstrated in the current work offers a Cu recess controllability of up to 0.324 nm per cycle, indicating that it is a promising methodology to compensate the hurdles of CMP process in hybrid bonding implementation. Computational work using atomic-scale, molecular dynamics (MD) simulation was combined with the experimental findings to further understand the mechanism that mainly governs overall performance of the wet ALE process. The adsorption behavior of surface modifying chemicals on Cu surface represents that molecular packing is critical in determining per cycle resolution on the same chemical concentration basis. Additional analysis from angle distribution between normal direction of Cu surface and C-C bond of adsorbed molecules also confirms the importance of self-limited assembly to achieve exceptional Cu recess control for advanced 3D integration.