Atomic layer deposition of non-conformal low dimensional ZnO thin films (Conference Presentation)

Abstract

Ultra-thin ZnO films were grown by atomic layer deposition (ALD) at a temperature of 60C on Si substrates and Si substrates coated with ~20nm of Al2O3 also deposited via ALD at 60C. Ellipsometry indicated ZnO films ranging in thickness from ~0.5 nm to ~7 nm. Atomic force microscopy results showed ZnO nano-islands formed prior to the completion of conformal atomic layers. AFM scans of 1um and 10um areas were employed in this study. This low dimensional ZnO islanding phenomenon was observed in both substrate types but with different incubation periods. The ZnO nano-islands on both substrates varied in diameter from ~20nm to ~100nm, island height variation ranged from ~2nm to ~9nm. ZnO nano-island formation had little to no incubation period on the Si substrates treated with ~20nm of Al2O3, and island formation was observed within 10 ZnO ALD cycles and nano-island density peaked around 20 to 30 ZnO ALD cycles. The highest rms roughness measurement obtained was of 0.7756 nm and is attributed to high nano-island density. While on bare Si the incubation period is significantly longer with nano-islands taking greater than 50 ZnO ALD cycles to form and achieving highest rms roughness of 0.25 nm around 60-70 ZnO ALD cycles. These results demonstrate non-conformal ultra-thin film growth by ALD, a deposition method expected to yield conformal thin films.