Comparison of Removal Efficiency of Cu Impurity on Si(100) Depending on the Cleaning Splits of (UV/O₃ + HF) and (H₂O₂ + HF)

Abstract

Si surface cleaning has been studied intensively in these days. One of the major concerns is about the removal of metallic impurities on Si surface. In this study we choose contaminant element of Cu which shows high electronegativity value compared to Si’s. The Si substrate was cleaned with using piranha (H₂SO₄:H₂O₂=4:1) and HF (HF:H₂O=1:100) solutions to eliminate the organic impurities and native oxide. The initial Si substrate was then contaminated intentionally by dipping into the 1 ppm standard solution of Cu and cleaned by the cleaning splits of the chemical solution HF combined with UV/O₃ treatment and the chemical mixture of H₂O₂ and HF. The initial substrates which were contaminated with the standard Cu solution exhibited the contamination levels of 10¹³–10¹⁵ atoms/cm² and these substrates were cleaned and showed Cu concentration down to the levels as lower as 10¹⁰ atom/cm² which were monitored by TXRF (total reflection X-ray fluorescence). And repeated treatments of these cleaning splits improved the surface microroughness of these initial substrate which were measured by AFM (atomic force microscope). The surface and interface morphologies contaminated with Cu were examined by SEM (scanning electron microscope) and TEM (transmission electron microscope). It was observed that Cu impurities were adsorbed on Si surface not in a thin film but in a particle form as a hemispherical shape. The chemical composition of Cu impurities and interface between Cu and Si substrate was investigated by AES (Auger electron spectroscope). The result exhibited that Cu element adsorbed on Si surface by chemical adsorption and this resulted in oxidation of Si substrate.