Internal oxidation of vacancy agglomerates in Czochralski silicon wafers during high-temperature anneals

Fast pulled Czochralski silicon crystals usually contain large octahedral vacancy agglomerates. These voids are known as D defects, which degrade the integrity of thin gate oxides by causing time zero dielectric breakdown. After annealing the wafers at temperatures above 1100 °C, the gate oxide integrity is clearly improved. We show by theoretical estimation, light-scattering tomography and transmission electron microscopy studies that the vacancy agglomerates can be filled with silicon oxide by internal oxidation. This is brought about by diffusion of interstitial oxygen to the voids, which can be regarded as internal surfaces. In this way they become less detrimental for thin gate oxides, because now they consist of silicon oxide itself. However, they are still present in an octahedral-like geometry and can be observed by Brewster angle infrared light-scattering tomography.