Process-induced trapping of charge in PECVD dielectrics for RF MEMS capacitive switches

Charge-induced failure is recognized as the primary reliability issue in RF MEMS capacitive switches. In this paper, we present a simplified method for quantifying the effects of process-induced charging of PECVD dielectrics commonly used in the fabrication of these devices. Using this method, based on capacitance-voltage (C-V) measurements of MIS (metal-insulator-semiconductor) devices, we examined the charge behavior of PECVD silicon dioxide, nitride, and oxynitride films deposited at substrate temperatures of 250-350/spl deg/C. The results show that these PECVD dielectrics contain sufficient incorporated charge in their as-deposited state to inhibit reliable switch operation. Post-deposition, plasma-induced and electrical stresses were also found to negatively impact the charge behavior of these films. However, after an initial period of instability, chemical analysis showed film composition to be highly consistent, both across deposition runs and with post-deposition stress. We conclude by presenting potential techniques for mitigation of the incorporated charge observed in these PECVD dielectrics.