Activation energy of negative fixed charges in thermal ALD Al2O3

A study of the thermally activated negative fixed charges Q(tot) and the interface trap densities D-it at the interface between Si and thermal atomic-layer-deposited amorphous Al2O3 layers is presented. The thermal activation of Q(tot) and D-it was conducted at annealing temperatures between 220 degrees C and 500 degrees C for durations between 3 s and 38 h. The temperature-induced differences in Q(tot) and D-it were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of E-A = (2.2 +/- 0.2) eV and E-A = (2.3 +/- 0.7) eV for Q(tot) and D-it, respectively. For annealing temperatures from 350 degrees C to 500 degrees C, the changes in Q(tot) and D-it were similar for both p-and n-type doped Si samples. In contrast, at 220 degrees C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Q(tot) based on an electron hopping process between the silicon and Al2O3 through defects is proposed. Published by AIP Publishing.