Study of hydrogen states in a-Si:H films, dehydrogenization treatments and influence of hydrogen on nanosecond pulse laser crystallization of a-Si:H

Structures based on hydrogenated amorphous silicon (a-Si:H) films deposited on various substrates (including not refractory ones) are widely applied in giant microelectronics devices, such as flat panel displays based on active matrix thin-film transistors and solar cells. The a-Si:H films produced by plasma enhanced chemical vapor deposition (PECVD) methods, contain up to 40% atoms of hydrogen. The influence of hydrogen on the optical and electrical properties of the films and their degradation is important. Therefore, the development of express and non-destructive methods for control of the hydrogen concentration in thin films continues to be an actual task to date. Previously, from a comparative analysis of infrared (IR) spectroscopy and Raman scattering spectroscopy, the ratios of the integral intensities of Raman peaks due to scattering by vibrations of the Si-H and Si-H-2 bonds to the intensity of Raman peak of the Si-Si bonds were experimentally determined. Knowing these ratios, it is possible to measure the hydrogen concentration, moreover, separately in Si-H and Si-H-2 states. Proposed quantitative method for determining of the hydrogen concentration from analysis of the Raman spectra is an express, non-destructive method and can be used for "in situ" monitoring of the hydrogen. The aim of this work was to determine the polarization dependence of Raman scattering by stretching vibrations of Si-H bonds and find the form of the corresponding Raman tensors. From analysis of Raman intensities in different polarizations the Raman tensors for Si-H and Si-H-2 bonds were determined. The regimes for dehydrogenization of thick (up to 1 micron) a-Si:H films were found. The nanosecond pulse XeCl laser with wavelength of 308 nm and pulse duration of 10 ns was used for pulse crystallization of as-deposited and dehydrogenated films. As it was studied earlier, for a-Si:H films with high hydrogen concentration, the threshold for crystallization is very close to threshold of laser ablation. As result of presented studying, it was obtained, that for pulse laser crystallization of a-Si:H films without damages and hydrogen blistering, the optimal concentration of hydrogen should be not higher than 10-15%. The developed approaches can be used for crystallization of a-Si:H films and based on these films nanostructures deposited on non-refractory substrates.