Hydrogen and nitrogen release processes in amorphous silicon nitride dielectrics have been studied by MeV ion scattering spectrometry in combination with infrared spectroscopy. The outdiffusion of those light constituents was activated by the thermal energy supplied to the samples by rapid thermal annealing treatments. Molecular models of how these reactions proceed have been proposed based on the information obtained from the infrared spectra, and the validity of the models has been tested by an analysis of the activation energy of the desorption processes. For this purpose, the evolution of the hydrogen concentration versus the annealing temperature was fitted to an Arrhenius-type law obtained from a second-order kinetics formulation of the reactions that are described by the proposed structural models. It was found that the low values of the activation energies can be consistently explained by the formation of hydrogen bonding interactions between Si-H or N-H groups and nearby doubly occupied nitrogen orbitals. This electrostatic interaction debilitates the Si-H or N-H bond and favors the release of hydrogen. The detailed mechanism of this process and the temperature range in which it takes place depend on the amount and the proportion of hydrogen in Si-H and N-H bonds. Samples with higher nitrogen content, in which all bonded hydrogen is in the form of N-H bonds, are more stable upon annealing than samples in which both Si-H and N-H bonds are detected. In those nitrogen-rich films only a loss of hydrogen is detected at the highest annealing temperatures.

We have analyzed the effects of rapid thermal annealing on the composition and on the bonding and optical properties of Ž . amorphous hydrogenated silicon nitride a-SiN :H thin films deposited at room temperature by the electron cyclotron x resonance plasma method. Films with three different as-grown compositions have been studied, namely x s 0.97, 1.43 and Ž 1.55. Annealing effects were related to film composition. In films with the presence of both Si-H and N-H bonds as-grown . compositions x s 0.97 and 1.43 , we found that a reorganization of bonds takes place at temperatures F 5008C, where the well-known cross linking reaction Si-Si q N-H™ Si-H q Si-N occurs without detectable release of hydrogen. In the same range of temperatures, an increase of the band gap was observed and attributed to Si-Si bond substitution for Si-H, but no Ž . changes in composition were detected. At higher temperatures T G 6008C , the optical gap decreases and both Si-H and N-H bonds are lost along with a release of hydrogen and nitrogen. For the films with an as-grown composition x s 1.55, we observe that the release of hydrogen only occurs at temperatures above 9008C, but it is not accompanied by any loss of nitrogen. An increase of the optical gap until the release of hydrogen begins and a decrease thereafter is observed.

No abstract

Thin polycrystalline films are often observed to develop a preferred orientation or texture that may have significant effects on film properties, especially in the case of anisotropic crystal structures. We report on a x-ray diffraction study of texture evolution in hexagonal ZnO:Al films, which were performed with a highly sensitive large-area detector enabling the investigation of films with thicknesses of some 10 nm only. In a set of magnetron-sputtered ZnO:Al films with thicknesses between 20 and 500 nm the resistivity was found to decrease with increasing thickness. A comprehensive texture analysis was performed within the framework of the series expansion method of the orientation distribution function (ODF). The investigations reveal a clear correlation between preferred grain orientation and electrical properties in ZnO:Al films. A general model is presented which relates the electronic mobility in polycrystalline films with the ODF by assuming the mobility to be composed of an intra-grain and an inter-grain fraction. It turns out that intra-grain anisotropy in ZnO:Al films cannot account for the observed variations in resistivity. Regarding the charge carrier scattering at grain boundaries the model relates the resistivity to the degree of grain alignment and makes use of the texture index J. On the basis of these assumptions it is shown that the resistivity scales with 1/J. The model also predicts the attainable minimum resistivity of thin ZnO:Al films with perfectly aligned crystallites which is in accordance with previously published results

The growth of microcrystalline silicon, μc-Si, films has been studied by infrared spectroscopy and x-ray diffraction. Thin films of various thickness have been prepared from SiH4–H2 mixtures by electron-cyclotron resonance chemical vapor deposition. Two structural transitions were observed during film growth. The first transition at a critical thickness of dac=9 nm manifested itself by a change from an initially amorphous growth to polycrystalline growth. The second structural transition was related to an increasing amount of silicon grains of preferred orientation with (110) lattice planes parallel to the substrate. The population of such (110)-oriented grains N110 was found to become dominant at about d110=310 nm, which may be considered as a second critical thickness above which the film exhibits a (110) fiber texture. The increase of N110 with increasing thickness follows a d1/6 dependence. The effect is understood in terms of an interplay between etching and deposition during growth.