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ASHUTOSH MISRA AND BUD L. SCHMIDT, Air Liquide Electronics Chemicals & Services, Inc., Dallas, TX, USA
LINDSEY HALL, JENNIFER SEES AND TRACE Q. HURD, Texas Instruments, Inc., Dallas, TX, USA

ABSTRACT

The detrimental impact of metallic impurities on device reliability and yield has been established in several previous studies. It is also known that roughening of the silicon surface as a result of contamination with light metals such as calcium can result in degradation of the gate oxide integrity (GOI). While many investigations of calcium adsorption from process chemicals such as SC1 and SC2 have been carried out to date [11–15], the phenomenon of calcium adsorption on silicon and silicon oxide surfaces from deionized water is not clearly understood. Mouche et al. concluded in their study that the amount of calcium adsorbing on silicon oxide surfaces from deionized water is higher than in SC1 solution, and that such adsorption reaches a plateau in surface concentration above 2 ppb in solution. A similar phenomenon was observed for copper and aluminium deposition from deionized water in their study. In a recent study, Loewenstein and Mertens have observed that calcium contamination on silicon oxide surfaces can be reduced substantially by reducing the pH of the medium. It is generally believed that calcium adsorption from DI water proceeds by the attraction of Ca2+ ions to the negatively charged silicon oxide surface and subsequent reaction with the Si–OH functions, giving rise to deposits.