Strong, high-yield and low-temperature thermocompression silicon wafer-level bonding with gold

Abstract

A systematic variation of process parameters for wafer-level thermocompression bonding with gold is presented for the first time. The process was optimized for high bond strength and high bond yield. In addition, the impact of the process temperature was investigated. A bond strength of 10.7 ± 4.5 MPa and a bond yield of 89% was achieved when bonding a wafer pair at 298 °C applying 4 MPa pressure for 45 min. A total of ten wafer pairs were bonded in a custom-built bonding tool and tested to establish the optimal process parameters. The bonded interface was found to be strong and dense enough for MEMS applications. The bonds were characterized using pull tests, transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). The TEM inspections indicated that it is possible to form hermetic seals by using the presented bonding method.