The fabrication and characterization of MOSFETs with titanium dioxide and hafnium dioxide as gate dielectrics.

摘要

In this thesis, TiO₂ and HfO₂ films were studied as possible candidates. The films were deposited from their respective nitrato precursors using the MOCVD method. For TiO₂ films, an interfacial layer was formed by thermal nitridation or plasma-aided nitridation of the silicon substrate surface prior to high permittivity film deposition.; The results obtained from TiO₂ MOS capacitors and transistors indicated that the higher nitridation temperature results in higher concentration of nitrogen and more positive charge.; The best result in terms of EOT was obtained from TiO₂ directly on silicon substrate samples. The positive charge in the interface is approximately on the high order of 1012 cm−2. The leakage current for TiO₂ deposited directly on silicon with an EOT = 16 Å is about 4 orders of magnitude lower than that of 16 Å thermal SiO₂ at −1.0 V bias. The maximum electron mobility is approximately 113 cm2/V·s, which is about one third of that for SiO ₂/Si interface at the effective field investigated.; HfO₂ films deposited at 300°C are monoclinic and oxygen rich. However, the excess oxygen seems to have no apparent effect on the electrical properties of films. The permittivity of HfO₂ deposited at 300°C is 17. The interfacial layer is amorphous and believed to be an oxynitride.; The HfO₂ film demonstrated excellent thermal stability. The HfO₂ films can sustain at least a 1000°C 5 seconds anneal without degrading the film quality and causing additional interfacial layer growth.; n-MOSFETs and p-MOSFETs with HfO₂ gate dielectrics were fabricated using a non-self aligned process. The minimum EOT achieved is 16 Å with polysilicon as the gate electrode. These transistors behave properly and demonstrated characteristics compatible to the oxynitride gate dielectrics. The n-channel subthreshold slope for HfO₂ deposited at 300°C without annealing is approximately 76 mV/Dec, and high temperature annealing improved the subthreshold slope to 70 mV/Dec. P-channel devices, however, had a higher interface state density and larger inverse subthreshold slopes. Both the hole and electron mobility are approximately the same as conventional transistors with oxynitride as gate dielectrics.