Effects of Ambient and Dissolved Oxygen Concentration in Ultrapure Water on Initial Growth of Native Oxide on a Silicon (100) Surface

Abstract

The effects of ambient and dissolved oxygen concentration in ultrapure water ͑UPW͒ on native oxide growth were studied at room temperature using a silicon ͑100͒ surface. Studies focused on the initial stage of the surface oxidation immediately after the HF cleaning. The silicon surfaces were exposed at a fixed duration to the UPW with different dissolved oxygen concentrations, open air, and dry nitrogen, respectively. The SiO 2 equivalent thicknesses of the native oxides formed were then measured and compared. Results indicate that the ambient and the dissolved oxygen concentration in UPW dramatically affect the growth rate of the native oxide. Decreasing the dissolved oxygen concentration in UPW and using an inert and dry atmosphere for the ultracleaning is shown to reduce or eventually prevent the native oxide from growing on silicon surfaces. The SiO 2 equivalent thicknesses of the native oxide formed on these surfaces were characterized by a rapid acid extraction followed by a determination for extractable silicon. The extractable silicon was determined by a high-resolution magnetic-sector ICP mass spectrometer. This analytical method has been demonstrated for measurement of an oxide thickness on a silicon wafer surface down to a monolayer range with a possible 0.1 Å resolution.The presence of interfacial native oxide on a silicon surface has widely been recognized as an impediment to the formation of highquality ultrathin gate, atomic layer epitaxy, and small metal contacts on the surfaces. 1-3 Suppressing oxide growth during the surface cleaning and precisely controlling the interface prior to the advanced ULSI processes have become absolutely critical. This recognition has led to considerable efforts of studying the mechanism of the native oxide growth and developing new measuring techniques that are capable of detecting the ultrathin native oxide formed on a silicon surface.The objective of this paper is to extend our previous studies 4,5 of ultrathin native oxide growth on an HF-cleaned silicon ͑100͒ surface and to improve the technique used for oxide thickness measurements. Previous studies dealt with the effects of UPW exposure time on a bare wafer and showed that native oxide grew immediately during a UPW rinse. The growth rate was found to increase linearly with increasing exposure time during the first 10 min of the rinse. 4,5 The emphasis of this paper is, however, placed on the effects of the ambient and the dissolved oxygen concentration in UPW. The initial stage of the surface oxidation during the first 10 min of the UPW rinse is still the focus. It is the authors' belief that the initial surface oxidation may be closely related to the reaction mechanisms governing the initiation and kinetics of native oxide formation on a silicon wafer surface. This study of the initial surface oxidation is thereby of practical importance to better understand the mechanisms and to find the solutions to suppress the growth of native oxide during UPW rinse and storage processes.In order to carry out such a study,...

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