Surface Charge Analysis of Ultrathin HfO2 , SiO2 , and Si3 N 4

Surface charge analysis (SCA) was used to characterize the interface properties of very thin chemical vapor deposited (CVD) HfO 2 , thermal SiO 2 , and thermal Si 3 N 4 films on Si. The thickness dependence of flatband charge Q FB indicates that negative charge exists at the HfO 2 /Si interface, while a positive charge exists in the bulk of the HfO 2 film. The interface state density, D IT , for as-deposited HfO 2 was found to be almost identical to a clean, bare Si surface, and degraded upon exposure to clean room ambient. Degradation during the process of wafer loading into a low pressure CVD furnace was more severe, a factor of four increase in D IT was seen. Annealing in forming gas was found to be effective for reducing D IT . For SiO 2 and Si 3 N 4 films, high-temperature annealing in N 2 was found to be effective for reducing both Q FB and D IT . Hole traps and positive Q FB were observed in SiO 2 , whereas electron traps and negative Q FB were seen in Si 3 N 4 .

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