Activation energy of negative fixed charges in thermal ALD Al_2O_3

摘要

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 Al_2O_3 layers is presented. The thermal activation of Q_(tot) and D_(it) was conducted at annealing temperatures between 220 ℃ and 500 ℃ 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 ℃ to 500 ℃, the changes in Q_(tot) and D_(it) were similar for both p-and w-type doped Si samples. In contrast, at 220 ℃ 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 Al_2O_3 through defects is proposed.