Effect of silicon surface termination on copper deposition in deionized water

The prevention of metal contamination on silicon wafer surfaces is a stringent issue in the semiconductor fabrication industry, because metals induce device degradation. Particularly, it has been reported that Cu contaminants on silicon surfaces deteriorate the integrity of gate oxide formed on that surface. We have investigated the relationship between Cu deposition and silicon surface termination in order to suggest a way to suppress Cu contamination during the wafer cleaning process. The effect of the microroughness and kink site density of silicon (111) and (100) surfaces on Cu deposition has been elucidated, using as a model system hydrogen-terminated samples exposed to deionized water with a known amount of dissolved Cu²⁺ to simulate a contaminated rinse bath. Under identical contamination conditions, the hydrogen-terminated Si(111) surface [H-Si(111)] with its flat monohydride terraces has an order-of-magnitude lower Cu coverage than the microscopically rough, hydrogen-terminated Si(100) surface [H_x-Si(100)]. Si(111) wafers that were misoriented between 1 and 8° from the (111) plane toward the (110) plane were used to investigate the effect of step density on Cu deposition. The results showed the change in Cu coverage as a function of step density on H-Si(111) surfaces was negligible compared to that shown between H-Si(111) and H_x-Si(100) surfaces. We suggest that the difference in the densities of dihydride (Si-H₂) sites on the H-Si(111) and H_x-Si(100) surfaces is the cause of the difference in Cu coverage. The dihydride densities of misoriented H-Si(111) surfaces are expected to be very low compared with those on H_x-Si(100). Hydrogen and methoxy-terminated surfaces were also compared to understand the effect of alternative terminations on Cu nucleation. The methoxy-terminated Si(100) surface had lower Cu coverage than H_x-Si(100). Deactivation of dihydride sites on the methoxy-terminated surface may be the reason for its better resistance to Cu contaminants.