Characterization of Oxidation-Induced Stacking Fault Rings in Cz Silicon: Photoluminescence Imaging and Visual Inspection After Wright etch

AbstractOxidation-induced stacking fault rings in polished Cz silicon samples before and after thermal wet oxidation are investigated by use of photoluminescence imaging. Currently the standard procedure for OSF ring detection is to expose the samples to a toxic preferential etchant, e.g. a Wright solution, after a thermal oxidation. This solution primarily attacks the regions with stacking faults, allowing detection by visual inspection. Samples from the seed end of p-type Cz silicon ingots with resistivities of approximately 1Ohm-cm were measured by PL imaging before and after a thermal oxidation process. Subsequently, Wright-etching was performed on the oxidized samples to expose stacking faults. The lifetime variations in the PL images were correlated with the location of the rings in the preferentially etched surfaces, and good agreement was found. The results show that for this crystal pulling process, even the PL images of unpassivated polished samples can be used to detect the OSF ring location. The thermal oxidation at 1100°C enhanced the contrast between the OSF ring and the rest of the sample in the PL image

Mechanisms of void formation in Ge implanted SiO2 films

The present paper reports on annealing of Ge implanted SiO2 films and emphasize the observation of voids and the mechanism behind their formation which is considered new. Samples were prepared by ion implanting fluences of 3×1016 and 1×1017 cm-2 respectively of 100 keV Ge into amorphous SiO2 films which were subsequently annealed up to 1000 °C in a N2 atmosphere. The structure of the films was studied by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). The most striking of the observations is that spherical voids with diameters up to tens of nanometers are observed in the films after annealing at 1000 °C for 1 h. The volume fraction of voids increases with the Ge fluence. The mechanism behind the void formation is indicated by the evolution of the sample structure after increasing annealing time or temperature; Ge first segregates into nanocrystals which then increase in size by diffusion and Oswald ripening. Ge is quite mobile in SiO2, and as oxygen or moisture from the annealing atmosphere diffuse in from the surface, the Ge will be bonded in an oxide closer to the surface than the precipitate. There is thus a net flux of Ge out of the nanoprecipitate into an oxide closer to the surface. The volume occupied by the Ge precipitate becomes a void. This model is discussed and it is concluded that it fits the observations. We also report on the filling of the voids by beam induced migration under TEM electron beam exposure