Composition, Chemical Structure and Electrical Properties of Thin Silicon Oxides Prepared by Oxidation of Silicon in Nitrous Oxide
In the continuing effort to scale down metal-oxide -semiconductor (MOS) devices, there is a need for high quality thin dielectrics. Growth of silicon oxides in nitrous oxide (N_2O) incorporates a small amount of nitrogen in the SiO_2 , and improves the electrical properties compared to conventional oxides grown in oxygen. This thesis describes correlations between the composition, chemical structure, and electrical properties of N_2O -grown oxides. X-ray photoelectron spectroscopy (XPS) is used, in conjunction with high-resolution chemical depth profiling, to obtain chemical and compositional information with a depth resolution of 10 A. Electrical measurements of interface states are made using MOS capacitors. The nitrogen distribution is different for oxides grown by conventional furnace oxidation and rapid thermal oxidation (RTO). The furnace oxides have a uniform distribution of nitrogen in the film, whereas the RTO oxides have a peak of nitrogen at the Si-SiO_2 interface, and no nitrogen beyond 30 A from the interface. These different distributions are the result of a reaction that takes place during RTO in N_2O, removing nitrogen from the oxide. A reduction in interface state generation for N_2O oxides compared to O_2 oxides has been observed, and is correlated with the nitrogen content within 20 A of the interface. Nitrogen which is incorporated further from the interface is less effective at inhibiting interface state generation. The importance of interfacial nitrogen has only been observed because of the high-resolution depth profiling used in this work. The chemical bonds of the nitrogen atoms in the oxide are studied with XPS. The results are consistent with the nitrogen atoms located more than 30 A from the Si-SiO_2 interface bonding to two silicon atoms with one remaining dangling bond. The nitrogen atoms are three-fold coordinated with silicon atoms near the interface. The three-fold coordination at the interface is postulated to play a role in the reduced interface state generation. The thesis concludes with a summary of the important results, and an assessment of the prospects for the use of N_2O oxides in MOS devices.
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- Physics: Condensed Matter; Engineering: Electronics and Electrical; Engineering: Materials Science