Surface activated bonding of Au/Ta layers after degas annealing for MEMS packaging

Au thin films with atomically smooth surfaces on Cr or Ta underlayers were bonded after a degas annealing treatment for MEMS packaging. In the case of bonding after the degas annealing step at 200 °C for 600 s in vacuum, the Cr/Au films were poorly bonded though the Ta/Au films were strongly bonded. This is because Cr
₂
O
₃
was formed on the Cr/Au film surface during the degas annealing step, but Ta was absent on the Ta/Au film after the degas annealing step. We expected that packaging with Ta/Au sealing layers allows low-temperature MEMS-packaging process after degas annealing.