STUDY OF MORPHOLOGY AND STRESS OF SILICON-ON-INSULATOR BY OPTICAL REFLECTANCE SPECTROSCOPY

Silicon-on-insulator material was prepared by implanting a high dose of nitrogen into crystalline silicon at an energy of 160 keV and a substrate temperature of 550-degrees-C to form a buried layer of silicon nitride. Ultraviolet reflectance spectroscopy was employed to characterize the silicon surface layer, while the silicon nitride phase was identified by means of infrared reflectance. In this paper the isothermal annealing behaviour of the material is investigated with regard to amorphization, stress and the formation of the insulator. Measured UV-reflectance of the samples is compared to simulated reflectance data which were obtained by modelling the implanted material as a layered structure with the surface layer consisting of mixed amorphous and crystalline silicon. From these simulations the percentage recrystallization after each annealing cycle was determined quantitatively. Stress in the surface layer was estimated by considering the shift in the positions of the energies at which reflectance maxima occurred in the ultraviolet. The 120 min anneal at 1200-degrees-C proved adequate for restoring the surface layer to a single crystalline state and for relieving the stress.