Ιn situ N₂-NH₃ plasma pre-treatment of silicon substrate enhances the initial growth and restricts the substrate oxidation during alumina ALD

The initial substrate inhibiting island growth and the formation of an interfacial layer with uncontrollable characteristics are the two main drawbacks of the Atomic Layer Deposition (ALD) of high-k metal-oxide gate dielectrics on silicon (Si). In this paper, we investigate the ALD of Al₂O₃ films from trimethyl aluminum and H₂O, on fluorhydric acid (HF) cleaned, as well as on HF-cleaned and in situ N₂-NH₃ plasma pretreated Si between 0 and 75 cycles. The films and their interface were characterized via Scanning Transmission Electron Microscopy coupled to Energy-Dispersive X-ray spectroscopy. The initial deposition is clearly increased on the pretreated surfaces, obtaining a linear ALD regime even after 5 ALD cycles, compared to several tens of cycles needed on HF-cleaned Si. Furthermore, a Si_xN_y layer is formed by the N₂-NH₃ plasma pretreatment, which acts as a barrier layer, reducing the oxidation of the Si substrate beneath it. This analysis provides a general framework for the understanding and determination of adequate surface pretreatments, able to combat the substrate inhibited initial growth and the Si oxidation during metal-oxide ALD on Si.