Comparison of Removal Efficiency of Cu Impurity on Si(100) Depending on the Cleaning Splits of (UV/O 3 + HF) and (H 2 O
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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 (H 2SO 4:H20 2=4:l) and HF (HF:H 20=I:100) solutions to eliminate the organic impurities and native oxide. The initial Si substrate was then contaminated intentionally by dipping into the 1ppm standard solution of Cu and cleaned by the cleaning splits of the chemical solution HF
combined with
UV/0 3 treatment and the chemical mixture of H20 2 and HF. The initial substrates which were 2 contaminated with the standard Cu solution exhibited the contamination levels of 1013- 1015 atoms/cm and these substrates were cleaned and showed Cu concentration down to the levels as
lower as 1010
atom/cm 2 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.
INTRODUCTION Recently, the device manufacturing technology is moving toward the deep sub micron structures. ULSI (ultra large scale integration) technology requires more stringent and reliable means to control the surface smoothness, organics'), particles, and metalliC2ý) contamination on the silicon substrate 7" ), than does VLSI (very large scale integration) technology. The most common process used today is the RCA wet chemical cleaning process 9). The RCA cleaning process was first developed by Kern and Poutinen from RCA and was published in 19709). The organic contaminants can be removed by the piranha (H 2SO 4 -H20 2) and SC 1 (NH 4OH-H 20 2-H20). The metallic contaminants can be eliminated by SC2 (HCI-H 20 2-H20) solution. But if the electronegativity values of metallic'()))) impurities exhibit higher values than that of Si, these metallic impurities such as Cu, Ag are very difficult to remove by wet chemical cleaning on the Si substrate12 ) 13). This wet chemical process based on the RCA cleaning has
253 Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
been used for more than 20 years and still dominant process to remove the contaminants on Si surface. In these days, the new cleaning concepts called dry cleaning method are under development to improve the removal of such contaminants. HF/l-1 20 vapor phase c
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