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Electrical characterization of ultrathin oxides of silicon grown by N<inf>2</inf>O plasma assisted oxidation
Date Issued
01-01-2000
Author(s)
Abstract
The ultrathin (2.0-3.5 nm) oxides of silicon have gained renewed importance in view of ultra large scale integration (ULSI) of the silicon devices. In the present investigation, the ultrathin oxides are grown on (100) oriented p-type single side polished silicon using N2O plasma assisted oxidation in a PECVD reactor at 200 °C. The oxide growth as a function of oxidation time is studied. The oxidation growth conforms to the reaction limited regime. In order to understand the electrical quality of Si/ultrathin SiO2 interface, Al-thin SiO2-Si tunnel capacitors are fabricated and their capacitance-voltage (C-V) and current-voltage (I-V) characteristics are studied. The effect of annealing on these oxides (termed as `post oxidation annealing') has also been studied. The C-V characteristics of tunnel capacitors with `as grown' oxide showed a frequency dependence, possibly due to the presence of large fast interface state density. These fast interface states are observed to decrease with increasing oxidation time. The tunnel capacitors that the oxides undergone `post oxidation annealing' (POA) at 350 °C in N2 ambient for 20 minutes have shown practically no frequency dependence of the C-V characteristics; this observation along with the data on I-V characteristics confirms that POA reduces the interface state density considerably. The forward and reverse currents of POA capacitors are observed to decrease considerably indicating the reduction in the trap assisted tunneling transport process across the tunnel insulator.
Volume
29