Plasma-Assisted ALD for the Conformal Deposition of SiO2: Process, Material and Electronic Properties

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).