CHARACTERISATIION OF DEFECTS IN TANTALUM PENTOXIDE FILMS BY THERMALLY STIMULATED CURRENT
JOSEPHINE L. PREMILA
JOSEPHINE L. PREMILA
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Abstract
The main focus of this project is the study of various annealing techniques to improve the quality of tantalum pentoxide (Ta2O5) films grown by low pressure metal-organic chemical vapour deposition (LPMOCVD) for 256Mb memory application. One of the most efficient and sensitive technique known as the thermally stimulated current (TSC) was used to characterise the defect states responsible for leakage current in Ta2O5 films. I-V measurement was done on all the samples to measure the leakage current which is an important criterion for the quality of the tantalum pentoxide film. Ta2O5 films deposited on p+ -Si and n+ -Si substrates were subjected to high temperature dry oxygen furnace annealing and low temperature oxygen plasma, nitrous oxide plasma, and ultra-violet oxygen annealing treatments. Each annealing process has shown a certain positive effect on the leakage current reduction and decrease in the defect density. The low temperature annealed samples showed greater reduction in the leakage current as compared to the high temperature annealed samples. The possible reason for this observation is that tantalum pentoxide films annealed at high temperatures are in the polycrystalline state and the grain boundaries in polycrystalline films are believed to be leakage sites whereas the low temperature annealed tantalum pentoxide films are in the amorphous state. It was found that among all the annealing treatments the samples which had undergone the nitrous oxide plasma annealing showed the lowest leakage current. It has also been demonstrated that the peak observed in the 100°K - 200°K region in the TSC spectra of the high temperature dry oxygen furnace annealed samples may be due to the diffusion of silicon from the silicon substrate into tantalum pentoxide and the peak in the 200°K - 300°K region in the TSC spectra of the low temperature ultra-violet oxygen annealed samples may be due to carbon contamination during the LPMOCVD process.
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1996
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