Microstructural and mechanical characterization of Cu/Sn SLID bonding utilizing Co as contact metallization layer

Most micro-electro-mechanical systems (MEMS) devices contain fragile moving parts, which poses challenges in process integration of interconnection methods requiring wet-chemistry, such as solid-liquid interdiffusion bonding (SLID). These sensitive MEMS structures can be protected from either the wet-chemistry or plated metals during chemical/electro-chemical plating SLID materials; however, this is a complex process. Hence, our previous research has investigated employing physically deposited contact metallization on wafers containing functional instead chemically layers (such electrochemical Cu). Co plausible layer for Cu-Sn bonding, it compatible with Cu–Sn systems. Furthermore, positively impact mechanical reliability intermetallic compounds (IMCs) due to stabilizing HT-hexagonal Cu 6 Sn 5 phase down room temperature and suppressing 3 formation subsequent void formation. However, critical control thickness achieve stable bond based bulk electroplated silicon chips. To utilize wafer-level necessary define appropriate metal stack. Consequently, present study four different stacks including A) 40nmTi/100nm Co, B) 40nm Ti/200nm Mo/100nm C) Ti/500nm D) Mo/500nm Co. More specifically, we evaluated microstructural evolution performance joints. Our revealed that Ti/Mo/100nm stack (4µm)Cu/(2µm)Sn composed IMCs (Cu,2.5at%Co) without remaining Sn. Moreover, joint contained negligible number voids even after long-time annealing at 150°C. analysis properties showed 1) tensile fracture surface exhibited mixture ductile brittle fractures, 2) Young’s modulus was higher than , while hardness were comparable. By stack, current able produce 25µm 10µm free (4µm Cu/2µm Sn) microbumps. • The thicknesses Cu/Sn significantly final reaction products quality. Void-free 2µm-Sn/4µm-Cu bonds achieved by utilizing sputtered device wafer. (Ti/Mo/100nm-Co/2µm-Sn/4µm-Cu) (Cu,Co) (Cu,2at%Co) IMC Co-Sn-Cu system E/H values formed system. Both facets dimples observed (Ti/Mo/100nm Co-2µm Sn-4µm Cu), indicating mixed ductile/brittle mode.