Developmental Research of an Apparatus for In-line Monitoring of Contamination on Si Wafer Surface

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In the fabrication of MOS devices, preparing chemically clean silicon surfaces is quite important. However, organic materials already present in the air may contaminate Si wafer surfaces prior to fabrication processes. Those materials cannot be completely removed by thermal annealing, and eventually affect the electrical performance of MOS devices. To fabricate high-quality, high-reliable MOS devices, therefore, we need an in-situ, rapid determination of the level of organic contamination on Si wafer surfaces during the fabrication process of the devices. In this study, an IR monitoring system has been developed for the rapid detection and characterization of organic contamination on Si wafer surfaces. IR light propagates through the Si wafer, internally reflecting many times, which makes it possible to detect small amounts of surface contamination on the wafer surface.We have performed an experiment demonstrating the feasibility of infrared absorption monitoring of organic contaminants on a 300-mm-diameter Si wafer in the multiple internal reflection (MIR) geometry with modest means. The main purpose of the experiment is to show the detection limit of the present system for organic contamination and then to compare it with the reported upper limit of the contamination level that has no appreciable effect on the electrical performance of MOS devices, that is, 10^<12> carbon atoms/cm^2 . We found that the present system allows for the detection of hydrocarbon contamination on Si wafer surfaces with a contamination level of below 10^<11> carbon atoms /cm^2. The present results demonstrate that the proposed monitoring system is quite beneficial to the fabrication of high-quality electronic devices.