Charge transport in silicon nitride/silicon oxide double layers

Charge transport was studied in double layers of 150 nm silicon nitride and 300 nm silicon oxide on silicon substrate by determining the location of the charge centroid (mean charge depth) with a new method based on the evaluation of capacitance-voltage data in conjunction with surface potential measurements. The samples were charged at room temperature on their open nitride surface to potentials of about 100 V with a corona process. Measurements of the location of the charge centroid were performed after annealing periods at temperatures up to 600°C. The results show that positive charge is relatively immobile at the nitride surface at temperatures up to 200°C; at 400°C, it drifts through the nitride within hours to be trapped at the nitride/oxide interface. The charge is released from these traps at about 500°C when it drifts to the substrate. Negative charge is also immobile at 200°C but drifts at 400°C through the entire double layer.