Moisture-induced capacitance-voltage instabilities in mesoporous silica thin films

Thin films of mesoporous silica (MPS) are attractive for low-permittivity interlayer isolation in integrated circuit wiring. Here, we report the mechanisms of moisture-induced capacitance-voltage (C-V) instabilities in MPS films. Upon annealing Al∕MPS∕Si(001)∕Al capacitors between 80 to 200 °C, the flat-band voltage first increases, reaches a maximum, and then decreases. Concurrently, the initially observed deep depletion behavior is replaced by strong inversion. Subsequent air exposure restores the preanneal C-V characteristics. Kinetics analyses reveal two thermally activated processes: Proton generation through fissure of silanol bonds (activation energy Ea1=0.42±0.04eV) and proton-induced depassivation of dangling bond traps (Ea2=0.54±0.05eV) at the MPS∕Si interface. We present an empirical model correlating these processes with the C-V characteristics. Our findings will be important considerations in designing processes for integrating MPS films into microdevices.