The rate of Cu dissolution from a Si(11i) wafer into an SC-i process solution was measured by total reflection X-ray spectroscopy. The Cu surface concentration decreased logarithmically with time, demonstrating that dissolution of Cu into an SC-i solution is a first-order process, probably kinetically limited by surface reaction.The rate constant at room temperature and a mixing ratio of 5:1:0.
An optical technique based on simple absorption spectroscopy has been demonstrated for monitoring metal contaminant deposition from aqueous processing solutions widely employed during microelectronics fabrication. Cu deposition from 0.15 and 0.25% HF solutions contaminated with 3.5 ppm Cu has been observed as a decrease in the absorption of a HeNe laser reflected at glancing incidence from a Si wafer. This is caused by the depletion of Cu2 from the mass-transfer boundary layer, providing direct evidence that Cu deposition is rate-limited by diffusion. This technique allows determination of which metallic species can deposit onto Si wafers in diffusion-limited processes during various aqueous processing steps in microelectronics manufacture. In addition, Cu deposition is seen to coincide with the completion of Si07 dissolution, confirming that Cu2 is reduced by an electroless process involving simultaneous Si oxidation. The decrease in absorption is consistent with a mass-transfer boundary layer thickness of about 335(20) lim. The optical absorption returns to its original value about 2 mm after the onset of deposition, consistent with diffusion-limited deposition of one monolayer of Cu, which is followed by a transition to a slowe surface rate-limited process.
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