THERMAL ANNEALING EFFECTS ON THE MECHANICAL-PROPERTIES OF PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITED SILICON-OXIDE FILMS

An annealing study was performed on nonstoichiometric amorphous SiOx (x < 2) films fabricated by plasma-enhanced chemical vapor deposition (PECVD) at 300-degrees-C using SiH4 and N2O 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-degrees-C. 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.