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A technique to image gate oxide integrity (GOI) defects across large gate areas has been developed. First, a low-ohmic bias pulse is used in order to break down nearly all GOI defects in a large area metal-oxide-semiconductor (MOS) structure. Then a periodic bias of typically 2 V is applied and the local heating caused by the leakage current through the broken GOI defects is imaged by infrared (IR) lock-in thermography. This method allows us to detect very small temperature variations down to 10 μK at a lateral resolution down to 10 μm. The determined defect densities in Czochralski silicon materials with various densities of crystal originated particles are in good agreement with charge-to-breakdown measurements of small area MOS capacitors. In conclusion, IR lock-in thermography provides a fast and reliable imaging technique of the lateral GOI defect distribution across the entire wafer area.

Using a method to study the grown-in defect density spectra in Czochralski silicon wafers by infrared light scattering tomography, we elucidate the changes in the size distribution of grown-in oxide precipitate nuclei caused by thermal processing at the beginning of a common CMOS device process. The first thermal step, screen oxidation at 900 • C, determines which parts of the grown-in defects grow to large stable defect formations and which of them shrink. The cooling rate of the crystal has a considerable influence on the defect evolution during CMOS processing. Low cooling rates result in lower defect densities than high cooling rates, although the total density of as-grown nuclei is the same. However, the maximum of their size distribution is located at a lower stability temperature for the low cooling rate than for the high cooling rate. This is important for their ability to grow during the first thermal step of the CMOS process. It also demonstrates that the choice of the appropriate silicon material is important for defect generation during processing and consequently also for the device yield.