Impact of wet-chemical cleaning on the passivation quality of Al2O3 layers

In order to enhance the passivation quality of thin Al₂O₃ layers an appropriate pre-deposition cleaning is expected to play an important role. In this study we present findings on the influence of the pre-deposition cleaning, post-deposition treatment and surface roughness on the passivation quality of thin ALD Al₂O₃ layers in an Al₂O₃/SiN_x stack. Especially for 0.5 nm layers of Al₂O₃ we found that there is a distinct influence of the cleaning on the passivation quality. With RCA cleaning surface recombination values below 10 cm/s on p-type 1 Ω cm Si could be reached for Al₂O₃ layers of 5 nm as well as of 0.5 nm thickness. Also the influence of surface roughness was examined. With smoothed wafers we found an influence of the surface morphology on all process parameters especially the post-deposition treatment. Additionally a slight trend towards decreasing surface recombination velocity with decreasing nano-roughness could be seen.