To manufacture ULSI devices with high performance and reliability in large volume, further integration and miniatur: ization are being promoted. The key issue in realizing what we call "Noise-Free Manufacturing" is to keep the wafer surface ultraclean all the time. To realize the ultraclean wafer, organic impurities adsorbed on the wafer surface must be removed first before other wafer cleaning procedures. This is because native oxide and metallic impurities on the wafer
Ultrapure water production technology is basic to ultralarge scale integrated (ULSI) manufacturing. To improve cleanliness on the Si surface, impurities in ultrapure water must be reduced. In a study of ozone behavior in ultrapure water the reaction order of ozone decomposition was 1.5 in ultrapure water inside oxidation‐passivated stainless steel tubing. However, inside plastic tubing the reaction order of ozone decomposition was not 1.5 even when impurities including organic materials in ultrapure water were suppressed to an extremely low level. Oxidation‐passivated SUS316L stainless steel resisted elution and ozone attack excellently. To perform continuous ozone sterilization, a new ultrapure water production system employing oxidation‐passivated stainless steel was developed. Ozone was injected into ultrapure water immediately after point of use and was removed at the outlet of the ultrapure water tank. In this system, bacteria were not detected in ultrapure water even when ozone concentration at the inlet of the ultrapure water tank was as low as 50 ppb. Other impurities also were suppressed below the detection limit. Continuous ozone sterilization brings about nonstop ultrapure water production.
An improved high purity hydrogen peroxide was developed for advanced semiconductor devices manufacturing. After treatment of a Si wafer with this hydrogen peroxide, no metallic impurity was adsorbed onto the Si wafer surface. However, a few parts per million of organic impurities remain in the hydrogen peroxide as total organic carbon (TOC). These organic impurities result from the production process for raw hydrogen peroxide and are identified as formic acid, acetic acid, and cyclohexanone deviatives. To examine the influence of organic impurities on semiconductor devices, we evaluated the electrical characteristics of metal oxide semiconductor (MOS) diodes with thermal oxide films, including chemical oxide by treatment with the improved hydrogen peroxide. In spite of high organic impurity content, the experimental results show that the organic impurities in the hydrogen peroxide did not affect the properties of MOS diodes with about 9 nm oxide films.
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