Nitrogen induced states at the CNx/Si interface

The deposition of carbon nitride (CNx) films onto n-type silicon wafers by rf magnetron sputtering at room temperature produces insulating films suitable for electronic applications. The traps at the CNx/Si interface may hamper the creation of electronic devices especially in VLSI applications. While amorphous carbon films have been studied for that purpose, the introduction of nitrogen inside the growth chamber adds an extra parameter in the process. CNx films were grown with the N2 concentration ranging between 1 and 25%. The effect of various N2 concentrations on the interface states is investigated in the present work. The interface states were characterized by admittance spectroscopy on metal-insulator-semiconductor (MIS) devices created by the deposition of A1 contacts. The density of interface states (Dit) and the corresponding time constants were obtained by the conductance technique. The Dit was found to extend between 5.5×1012 and 2.0×1013 eV−1 cm−2 depending on the N2 concentration. Annealing at 350°C reduced these values. Typical values for the time constants were around 10−4 s indicating that the traps are located close to the silicon midgap.