Toward Selective Ultra-High-Vacuum Atomic Layer Deposition of Metal Oxides on Si(100)

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The selectivity of clean Si(100)-(2 × 1) surfaces fully reacted with H 2 O- and hydrogen-passivated Si(100)-(2 × 1) surfaces is investigated for atomic layer deposition (ALD) of TiO 2, Al 2 O 3, and HfO 2 using TiCl 4, TMA, or TDMA-Hf precursors with H 2 O, respectively, in an ultra-high-vacuum (UHV) environment. The initial reaction probability is estimated by determining the minimum exposure necessary for complete reaction of the metal precursors on both H 2 O-reacted and H-passivated Si(100)-(2 × 1) surfaces and examining the first full cycle of the ALD process for each oxide. Under these UHV conditions, the first cycle selectivity is 17:1 for TiO 2, 37:1 for Al 2 O 3, and only 4:3 for HfO 2 . Additionally, TMA is found to react with approximately half of the Si-H sites in addition to all the Si-OH sites, while TiCl 4 and TDMA-Hf gases are found to react principally with the surface −OH on H 2 O-reacted Si(100) surfaces with no reaction with the −H sites.