Doping sites observation of deep-level impurities in hyperdoped silicon via high-resolution transmission electron microscopy

Abstract

The direct observation of the doping sites of deep-level impurities in hyperdoped silicon is essential to determine the impurity diffusion, distribution, and precipitation via different hyperdoping processes or thermal annealing conditions. This is crucial to clarify the functioning of a mechanism, which can improve the impurity electroactivity. However, this observation, which is usually performed by using high-resolution transmission electron microscopy (HRTEM), is limited by some restrictions in the microscopic imaging conditions, such as the microscope resolution, the defocus of the objective lens, the specimen thickness, and the projected orientation of the specimen (i.e. the zone axis). Therefore, to eliminate these restrictions, conventional field-emission-gun HRTEM images in combination with image processing (deconvolution) were investigated in order to obtain structure images with atomic resolution. Both the substitutional and the interstitial doping sites of oxygen, chalcogen (sulfur and selenium), and transition metal (titanium and cobalt) impurities in silicon were determined by image contrast analysis. Finally, the favorable conditions for the direct observation of doping sites were defined.