Characterization of low temperature Cu/In bonding for fine-pitch interconnects in three-dimensional integration

This study presents the results for Cu/In bonding based on the solid-liquid interdiffusion (SLID) principle for fine-pitch interconnects in threedimensional integration. The microbumps were fabricated on Si wafers (55 mu m pitch, 25 mu m top bump diameter, 35 mu m bottom bump diameter). In was electroplated directly on Cu only on the top die microbumps. Two different In thicknesses were manufactured (3 and 5 mu m). The interconnects were successfully fabricated at a bonding temperature of 170 degrees C. High temperature storage was carried out at 150 and 200 degrees C for different times between 2 and 72 h directly after the interconnect formation in order to investigate the temperature stability. The microstructure was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The intermetallic compound (IMC) found in the microbumps after electroplating was CuIn2. The intermetallic interlayer consists of Cu11In9 and a thin layer of Cu2In after bonding and isothermal storage. (C) 2018 The Japan Society of Applied Physics