SiO2-passivation layers formed by thermal oxidation and various chemical vapor deposition (CVD) processes have been investigated by infrared spectroscopy and wet chemical etching studies in ammonium hydroxide water solutions. In order to obtain effects of thermal annealing on the dislocation structure of deposited oxides, these layers have been subjected to an annealing step. Disorder and water-related features in infrared spectra, as compared to activation energies and etch rates received from the etching experiments, show mainly two effects: the annealing of deposited films is accompanied by bond strain relaxation through viscous flow and decreased porosity without a measurable decrease in thickness. Within the infrared study, further evidence was obtained for disorder-induced mechanical mode coupling in oxides with a dislocation structure. In addition, the infrared spectroscopic and etching results for thermally grown oxides are very similar to those for annealed CVD oxides. Such a similarity was also obtained for unmodified CVD oxides processed at two very different temperatures.
An annealing study was performed on nonstoichiometric amorphous SiO= (x < 2) films fabricated by plasmaenhanced chemical vapor deposition (PECVD) at 300~ using Sill4 and N20 chemistry. After deposition, these layers contain hydrogen and nitrogen impurities, which were found to play a major role in the explanation of the properties of annealed films. Fourier transform infrared absorption spectra of plasma enhanced vapor deposited oxide layers annealed at elevated temperatures show approximately the same features as the spectra of thermal oxide films. This similarity demonstrates the ability of PECVD oxides to form a regular network of Si-O tetrahedrals. From distinct deviations in these spectra, the participation of Si-N bonds located within the Si-O network is concluded. The participation of Si-N bonds is also confirmed by the estimation of the activation energies in wet chemical etching studies using ammonium hydroxide water solution. The mechanical stress of the PECVD oxides clearly depends on the deposition conditions and their thermal history. With increasing annealing temperature the intrinsic stress increases until a maximum film stress value is reached between 700 and 800~ Above this temperature the intrinsic stress is continuously reduced until the total stress approaches the value of the thermal film stress. This is explained mainly by hydrogen desorption, Si-N bond formation, and SiO2 bond rearrangement processes. Depending on deposition conditions and postannealing steps, it is possible to design layers with a predefined stress.
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