Surface passivation by Al2O3 and a-SiNx: H films deposited on wet-chemically conditioned Si surfaces

The surface passivation of p- and n-type silicon by different chemically grown SiO2 films (prepared by HNO3, H2SO4/H2O2 and HCl/H2O2 treatments) was investigated after PECVD of a-SiNx:H and ALD of Al2O3 capping films. The wet chemically grown SiO2 films were compared to thermally grown SiO2 and the surface passivation was benchmarked against single-layer a-SiNx:H and Al2O3 films deposited on HF-last Si surfaces. Directly after PECVD and ALD the surface passivation was found to be similar for all chemically grown SiO2 stacks and higher than for the single-layer films. After annealing at 400°C the level of surface passivation improved but remained similar for the chemically grown SiO2 stacks. Corona charging experiments on the annealed chemically grown SiO2/Al2O3 stacks revealed that the fixed charge density, i.e. the field-effect passivation, was lower compared to single-layer Al2O3 films whereas the chemical passivation was found to be higher. The surface passivation was also investigated as a function of the annealing time. Chemically grown SiO2 stacks achieved the maximum level of surface passivation after annealing for half a minute which is different from the stacks with a-SiNx:H and Al2O3 films deposited on thermally grown SiO2 or HF-last Si surfaces which required considerably longer annealing times.