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

Plasma-assisted atomic layer deposition (ALD) was used to deposit SiO2 films in the temperature range of T-dep = 50-400 degrees C on Si(100). H2Si[N(C2H5)(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 (similar to 50 ms) were found to be sufficient to reach self-limiting ALD growth with a growth-per-cycle of similar to 1.2 angstrom (T-dep = similar to 200 degrees C) leading to SiO2 films with O/Si ratio of similar to 2.1. Moreover, the plasma ALD process led to a high conformality (95-100%) for trenches with aspect ratios of similar to 30. In addition, the electronic (interface) properties of ultrathin ALD SiO2 films and ALD SiO2/Al2O3 stacks were studied by capacitance-voltage and photoconductance decay measurements. The interface quality associated with SiO2 was improved significantly by using an ultrathin ALD Al2O3 capping layer and annealing. The interface defect densities decreased from similar to 1x10(12) eV(-1) cm(-2) (at mid gap) for single layer SiO2 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 SiO2 thickness (1-30 nm). (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.067203jes] All rights reserved.