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The material properties and c-Si surface passivation have been investigated for Al 2 O 3 films deposited using thermal and plasma atomic layer deposition ͑ALD͒ and plasma-enhanced chemical vapor deposition ͑PECVD͒ for temperatures ͑T dep ͒ between 25 and 400°C. Optimal surface passivation by ALD Al 2 O 3 was achieved at T dep = 150-250°C with S eff Ͻ 3 cm/s for ϳ2 ⍀ cm p-type c-Si. PECVD Al 2 O 3 provided a comparable high level of passivation for T dep = 150-300°C and contained a high fixed negative charge density of ϳ6 ϫ 10 12 cm −2 . Outstanding surface passivation performance was therefore obtained for thermal ALD, plasma ALD, and PECVD for a relatively wide range of Al 2 O 3 material properties. Al 2 O 3 recently emerged as an effective material for the passivation of crystalline silicon ͑c-Si͒ surfaces, enabling ultralow surface recombination velocities ͑S eff ͒ on p-, n-, and p + -type c-Si 1,2 leading to enhanced solar cell efficiencies. 3-5 A combination of chemical passivation ͑i.e., the reduction of interface defects͒ and field-effect passivation ͑i.e., electrostatic shielding of minority charge carriers͒ provided by a large amount of fixed negative charges located at the c-Si/Al 2 O 3 interface is key to the high level of surface passivation achieved. To date, the Al 2 O 3 surface passivation films were mostly synthesized by plasma and thermal atomic layer deposition ͑ALD͒ at a substrate temperature of ϳ200°C. 1-8 Very recently, it has been shown that other techniques, such as sputtering and plasmaenhanced chemical vapor deposition ͑PECVD͒, [9][10][11] can also be used to deposit Al 2 O 3 surface passivation films. These alternative deposition techniques allow for higher growth rates but generally do not surpass ALD in terms of material and surface passivation quality.In this article, the influence of the substrate temperature ͑T dep ͒ during deposition on the Al 2 O 3 material properties and the surface passivation performance is addressed for Al 2 O 3 films deposited at temperatures in the range of T dep = 25-400°C for thermal and plasma ALD and PECVD. We report that PECVD can be used to deposit Al 2 O 3 films that provide a similar level of surface passivation as ALD Al 2 O 3 while enabling higher deposition rates. By corona charging experiments, the presence of a high fixed negative charge density in the PECVD Al 2 O 3 films is demonstrated. ExperimentalA direct comparison between thermal ALD and plasma ALD was enabled by employing both methods in an Oxford Instruments OpAL ALD reactor ͑operating pressure ϳ170 mTorr͒ and in a second reactor, the Oxford Instruments FlexAL ͑operating pressure ϳ15 mTorr͒. For both ALD methods, trimethylaluminum ͓Al͑CH 3 ͒ 3 ͔ was used as the Al precursor in the first half cycle of the ALD process. During the second half cycle, either H 2 O or an O 2 plasma was used for thermal and plasma ALD, respectively. 7 Cycle and purge times were optimized to reach a truly self-limiting ALD process at every T dep . The PECVD process employed a continuous remote O 2 /Ar plasma an...

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).