Infrared Spectroscopic Characterization of Functional Monolayers on Silicon
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0901-Ra17-05.1
Infrared Spectroscopic Characterization of Functional Monolayers on Silicon N.L. Rowell, Li-Lin Tay, J.-M. Baribeau, R. Boukherroub1 and D.J. Lockwood National Research Council, Ottawa, Ontario, Canada K1A 0R6 1 Interdisciplinary Research Institute, 59652 Villeneuve d'Ascq, France ABSTRACT Infrared vibrational spectroscopy in an attenuated total reflection geometry has been employed to investigate the presence of organic and inorganic thin layers on Si-wafer surfaces. Three different processes were compared for surface contaminant removal; microwave plasma, UV-ozone, and a piranha solution cleaning. The CH vibrations at 2928 and 2856 cm-1 characteristic of organic contaminants were monitored before and after each cleaning procedure to determine how well it removed surface contaminants. We found that native oxide removal from the Si surface should only be carried out after a cleaning essay. We observed that surface oxide removal exposed a hydrophobic bare Si surface, attracting organic molecules present in solution or the ambient. A large increase of the CH vibrational signature was observed for a Si wafer after an HF dip. A combination of plasma cleaning followed by UV-Ozone treatment was found the most effective one for Si wafer cleaning. We were able to evaluate the effectiveness of the cleaning methods, hydrogen surface passivation and oxide removal/regrowth.
INTRODUCTION Recently there has been a large increase in Si-based biosensor activity. Central to this technology is the capability to form a self-assembled monolayer directly on the bare Si surface. Such layers provide surface functionality and biospecificity for subsequent molecular binding events. However, before growing functional layers, a Si wafer must undergo a stringent cleaning essay to remove whatever layers of organic contaminants and/or inorganic surface oxides are present. This crucial step then enables a subsequent successful growth of the particular functional monolayer being laid down on the wafer surface. The present work uses infrared (IR) vibrational spectroscopy in an attenuated total reflection (ATR) geometry to investigate the presence of organic and inorganic thin layers on Si-wafer surfaces. Three different Si wafer cleaning processes will be compared namely, microwave plasma, UV-ozone, and piranha solution cleaning. As a monitor the strength of the CH vibrations appearing at 2928 and 2856 cm-1 characteristic of organic contaminants were measured before and after each cleaning procedure to see its effectiveness for removing surface organic contaminants. With the ATR method, we evaluated the effectiveness of the cleaning methods and monitored hydrogen surface passivation. We will show that oxide removal and regrowth can be characterized with the same method. Clearly the objective of the cleaning procedure was to obtain silicon surfaces that were simultaneously free of organic molecules and clear of inorganic layers such as surface oxides.
EXPERIMENT The ATR method employed in the present work utilizes a high-index hemi
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