Characterisation of Surface Processes during Oxide CMP by in situ FTIR Spectroscopy with Microstructured Reflection Elem
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1249-E05-02
Characterisation of Surface Processes during Oxide CMP by in situ FTIR Spectroscopy with Microstructured Reflection Elements at Silicon Wafers Henrik Schumacher, Ulrich Künzelmann and Johann W. Bartha Institute of Semiconductors and Microsystem Technology, Dresden University of Technology, 01062 Dresden, Germany ABSTRACT In situ investigations of the chemical and mechanical mechanisms during CMP processes require analytical access to the wafer surface while interacting with the slurry and the pad under polishing conditions. In this study me make use of novel, specifically prepared, and self-designed Si wafer called microstructured single reflection elements (mSRE) utilizing the IR transparency of silicon [1]. The mSRE’s enable in and ex situ attenuated total reflection (ATR) Fourier transform infrared (FTIR) investigations at the interface between silicon and the ambient with an enhanced usable spectral range. So, a thin silicon oxide layer or the polishing slurry can be investigated in the entire mid and far infrared spectral region. These mSRE wafers were placed at a simple reflection accessory of a FTIR spectrometer and either wet etched by a buffered oxide etch or polished using a CMP equivalent polishing configuration. During CMP the change of typical vibration bands of SiO2 layers and slurry constituents are observed. It was shown that the sensitivity as well as the surface selectivity of the experimental setup enables slurry and thin-film characterisations within the thickness range of monolayers. Surprisingly, the spectral features of the pad have not been observed during the polishing investigations. INTRODUCTION Over the last 20 years chemical-mechanical planarization (CMP) has become a very important method for microelectronic device fabrication in semiconductor industries. It is used for planarization and smoothing a surface as well as to remove excess material after deposition over trenches due to the chemical and mechanical forces e.g. silicon dioxide in the shallow trench isolation (STI) process. Fundamental investigation of chemical and mechanical mechanisms in CMP requires the access to the wafer surface while interacting with the slurry and the pad under polishing conditions. Fourier transform infrared (FTIR) spectroscopy is a powerful and well established tool for the qualitative and quantitative characterisation of semiconductor substrates or thin inorganic as well as organic functional layers and their interfaces [2]. It provides structural information about molecular vibrations of characteristic groups, e.g. Si–H or Si–O. The FTIR technique of attenuated total reflection[3,4] (ATR) is very convenient in particular for in situ measurements within strongly IR absorbing environments, e.g. etching solutions or polishing slurries [5-8]. It is non-destructive, surface sensitive, and provides access to the substrate/sample interface entering from the substrate. In case of an internal reflection at the silicon/silicon dioxide interface ATR enables in situ measurements of strongly absorbing
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