Lowering bonding temperature for silver sintering to silicon and silicon carbide using silver oxide decomposition

Micron-scale Ag₂O paste facilitates direct sintering bonding to silicon and silicon ceramic substrates because of in-situ formation of Ag during the decomposition of Ag₂O. However, it remains difficult to obtain a high-strength joint at low bonding temperatures using the conventional process (even at 300 °C) despite their good performance at temperatures above the thermal decomposition temperature. In the present study, the dominant factors for low-temperature direct sintering bonding of Ag to Si and SiC substrates using Ag₂O decomposition were investigated by controlling the preheating temperature and evaluating the bondability. The influence of preheating temperature was evaluated using thermal analysis and the assessment of joint strength. Lower preheating temperatures led to higher joint strength at lower bonding temperatures. It was observed that Ag nanoparticles were generated during the preheating process at high temperatures, indicated from the occurrence of the exothermic Ag₂O decomposition reaction. However, the initial formation of Ag nanoparticles during the preheating process did not contribute to the sintering process. We propose that lowering the preheating temperature plays an important role in precisely controlling the amount of organic solvent required for the decomposition reaction of Ag₂O. Finally, we confirmed that the low-temperature preheating process realized a sound joint for the Ag sintering bonding to SiC, even at 300 °C.