Plasma-assisted atomic layer deposition (ALD) was used to deposit SiO 2 films in the temperature range of T dep = 50-400 • C on Si(100). H 2 Si[N(C 2 H 5 ) 2 ] 2 and an O 2 plasma were used as Si precursor and oxidant, respectively. The ALD growth process and material properties were characterized in detail. Ultrashort precursor doses (∼50 ms) were found to be sufficient to reach self-limiting ALD growth with a growth-per-cycle of ∼1.2 Å (T dep = ∼200 • C) leading to SiO 2 films with O/Si ratio of ∼2.1. Moreover, the plasma ALD process led to a high conformality (95-100%) for trenches with aspect ratios of ∼30. In addition, the electronic (interface) properties of ultrathin ALD SiO 2 films and ALD SiO 2 /Al 2 O 3 stacks were studied by capacitance-voltage and photoconductance decay measurements. The interface quality associated with SiO 2 was improved significantly by using an ultrathin ALD Al 2 O 3 capping layer and annealing. The interface defect densities decreased from ∼1×10 12 eV −1 cm −2 (at mid gap) for single layer SiO 2 to < 10 11 eV −1 cm −2 for the stacks. Correspondingly, ultralow surface recombination velocities < 3 cm/s were obtained for n-type Si. The density and polarity of the fixed charges associated with the stacks were found to be critically dependent on the SiO 2 thickness (1-30 nm).

Differences in Si surface passivation by aluminum oxide ͑Al 2 O 3 ͒ films synthesized using H 2 O and O 3-based thermal atomic layer deposition ͑ALD͒ and plasma ALD have been revealed. A low interface defect density of D it = ϳ 10 11 eV −1 cm −2 was obtained after annealing, independent of the oxidant. This low D it was found to be vital for the passivation performance. Field-effect passivation was less prominent for H 2 O-based ALD Al 2 O 3 before and after annealing, whereas for as-deposited ALD films with an O 2 plasma or O 3 as the oxidants, the field-effect passivation was impaired by a very high D it .

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