Impact of copper contamination on the quality of silicon oxides

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Abstract
To study the impact of metal contamination on the quality of gate oxides, (100) silicon wafers were intentionally contaminated with copper from the backside. The in-diffusion of copper and/or oxidation were performed in a rapid thermal annealing system. Gate oxide areas with low breakdown fields of about 2–3 MV/cm were located in a pinhole detector and correlate very well with the contaminated areas revealed by Secco defect etching. Using various analytical tools the failure mechanism was found to be related to the formation of Cu-rich precipitates at the SiO2/Si interface. Depending on the in-diffusion temperature (and hence on the supersaturation of Cu in Si), two different mechanisms were observed: At high supersaturation (1200 °C/30 s) Cu-rich silicide particles can bend, crack, and finally penetrate the oxide layer. At lower in-diffusion temperatures (900 °C/60 s) lens-shaped Cu silicides form at the SiO2/Si interface and reduce the oxide thickness.

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