Solid-Liquid Interdiffusion Bonding Based on Au-Sn Intermetallic for High Temperature Applications

This paper covers one of the aspects of solid-liquid interdiffusion (SLID) bonding of semiconductor structures to substrate for high temperature operation. Investigations were focused on Au/Sn intermetallic compounds formed at the interface between Au metallization on the chip and Sn metallization on the DBC (Direct Bonded Copper) substrate. Two version of SLID were applied: one stage process at 350 degrees C and two stage process short time at 280 degrees C + long time at 180 degrees C. Second process is divided into two steps: short high temperature (280 degrees C) step for melting Sn and initial intermetallic compound formation and long low temperature (180 degrees C) step for solid state diffusion process. Design of experiments technique was used for process optimization. The best process parameters were obtained and they were applied for monocrystalline GaN chips assembly to DBC substrates. In the long-term stability tests at 300 degrees C it was proven that both versions of investigated SLID technique can be applied for monocrystalline GaN chips assembly. Critical condition for this assembly operation is high enough pressure applied on the chip to initiate diffusion process.