Surface and Interface Characterization of Sequentially Plasma Activated Silicon, Silicon dioxide and Germanium Wafers for Low Temperature Bonding Applications

This article reports the sequentially plasma activated bonding (SPAB) of n-Ge with p-Si and SiO2 at low temperature. Surface activation resulted in highest hydrophilicity of Ge compared with Si and SiO2 counterparts. The highest hydrophilicity of Si, Ge and SiO2 induced by O2 RIE plasma was combined with their highest reactivity induced by MW N2 radicals while maintaining smooth surface roughness. Weak bonding strength of Si/Ge and SiO2/Ge in the SPAB at room temperature was improved after heating at 200°C, but they were still lower than that of Si/Si in the SPAB at room temperature, which is due to the unique reactivity of Ge. The deviation of the reverse bias behavior from a typical p-n junction is due to the low doping concentration in Ge. The degradation of current in the sequential heating resulted mainly from the oxidized surfaces of Ge and Si as well as the bonded interface.