Determination of Vacancy Concentration in Float Zone and Czochralski Silicon

Lattice vacancies in silicon play an important role in atomistic diffusion theories. They form mobile complexes with substitutional impurities and act as reaction partners for other defects in many of the different processing steps on the way from crystal growth to the finished devices. Knowledge of the spatial distribution of vacancies is a key to the explanation of various controversial reports of diffusion phenomena. Diffusion of platinum at low temperatures is a convenient way to characterize vacancy profiles in silicon. This presentation summarizes in short form the background of platinum diffusion and outlines the experimental procedure used to characterize vacancy concentrations. The applicability of the method is shown by experiments with three different kinds of samples: as-grown float zone wafers, as-grown Czochralski wafers, and Czochralski wafers which were preprocessed by rapid thermal annealing in nitrogen ambient at 1200 °C. Generally, in as-grown float zone samples, vacancy concentrations on the order of 10¹⁴ cm^¿3 were measured. In contrast, in as-grown CZ wafers, significantly lower concentrations of vacancies were found which increase by processing at 1200 °C.