Process Parameters for Formic Acid Treatment with Pt Catalyst for Cu Direct Bonding

Direct bonding of Cu in atmospheric pressure is required in various device interconnections. A technique using formic acid treatment with Pt catalyst has been proposed and applied to Cu bonding at a low temperature below 200 degrees C. The method consists of procedures of exposure of formic acid vapor to sample surfaces by Ar carrier gas in a closed chamber. After the formic acid treatment, the samples are pressed to each other under a contact pressure of several tens. One of the purposes of this study is to investigate the conditions in which the time for the formic acid treatment can be shortened as much as possible and the temperature for the formic acid treatment can be lowered as much as possible. The bonding parameters including the temperature and the time of the formic acid treatment were examined in the details to optimize the bonding characteristics In the previous study, it was shown that of 30 minutes was required for bonding at200 degrees C. However the present study shows that the bonding strength is greatly changed between 160 degrees C and 180 degrees C.