Novel Cu/SiCN surface topography control for 1 μm pitch hybrid wafer-to-wafer bonding

This paper presents our approach to hybrid bond scaling to 1 mu m pitch and recent demonstration results. The direct wafer stacking of two Cu/SiCN surface is realized between slightly protruding Cu nano-pad on one wafer and slightly recessed, but larger, Cu nano-pad on the second wafer. The protruding nano-pad is tailored as smaller than the recessed nano-pad to compensate for the overlay tolerance in the wafer-to-wafer (W2W) bonding. To control the stability and performance of Cu nano-pad integration process, the intensive inline atomic force microscopy (AFM) and surface acoustic microscopy (SAM) characterization is used on various test structures before/after wafer bonding. The surface flatness should be less than 1 nm/mu m to ensure void free bonding. This surface planarization is readily achieved for Cu pad densities up to 25%. Finally, we have demonstrated the high yield and low resistance performance across the 300mm wafer for hybrid bond pitches between 5 and 1 mu m.