Conduction Mechanisms of Ta/Porous SiCOH Films under Electrical Bias

In the present study, the electrical characteristics of metal-insulator-semiconductor capacitors with Cu and Ta electrodes on porous SiCOH dielectric subjected to bias-temperature stress (BTS) are investigated. The capacitor with Cu electrode exhibits stable capacitance-voltage (C-V) characteristics after being subjected to BTS of 0.5 MV/cm at 200 degrees C, while Ta ions readily drift into porous SiCOH under the BTS of 0.5 MV/cm and a lower temperature at 150 degrees C, as indicated by the observation of a larger flatband voltage shift during C-V sweep afterward. The leakage behavior of porous SiCOH is investigated using a voltage ramp method after the capacitors are subjected to BTS to study the conduction mechanism associated with the metal-ion drift into the dielectric. It appears that the leakage of capacitors with Ta electrodes starts to increase after BTS and falls into the Poole-Frenkel conduction regime, indicating that Ta ions drift into porous low-k under BTS and subsequently act as electron traps. The leakage of capacitors with Cu electrodes, however, retains almost the same characteristics as those before BTS, suggesting that the increase of leakage for capacitors with Ta electrodes is induced by the drifted Ta ions instead of the degradation of dielectric material. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2992125] All rights reserved.