Microdefects in nitrogen doped FZ silicon revealed by Li⁺ drifting

ULSI technology requires ultra-thin device oxides with excellent breakdown integrity. Recent studies have unveiled degraded dielectric breakdown voltage (DBV) performance of the ultra-thin oxides. These findings suggest that one source for poor oxide integrity is the incorporation of native defects from the Si substrate during oxide growth. Primary defect candidates are D defects which exist mostly in the central region of floating zone (FZ) grown Si crystals. Nitrogen (N) doping eliminates D defects, as detected by conventional means, and improves oxide integrity. Results are presented indicating the prevalence of microdefects in the central region of p-type nitrogen doped FZ Si using the method of Li ion (Li⁺) drifting in an electric field. A model has been developed based on Li interactions in Si which describes the Li⁺ precipitation mechanism. The mechanism establishes that vacancies are the most likely Li⁺ precipitation sites. The results are discussed in relation to breakdown mode patterns of polished FZ Si wafers after gate oxide tests.