금속 오염 제어를 위한 HF 기반 세정액에 대한 연구

Abstract

With continuous advancements in ultra large scale integrated (ULSI) fabrication technology, achieving of ultraclean wafer surface is essential. An ultraclean wafer surface is characterized as (a) particle free, (b) organic contamination free, (c) metallic contamination free, and (d) surface microroughness free. It is well known that the metallic contamination on the Si surface can cause the side effects on semiconductor devices such as, increase the current leakage at the p-n junction, decrease the oxide breakdown voltage, and accelerate the deterioration of carrier lifetime. It has been reported that the metallic contamination on the Si surface must be suppressed to 1× 〖10〗^10 atoms/cm2 to prevent the above defects. Wet chemical processing has been used as a major cleaning method in ULSI manufacturing. The biggest side effect of this RCA based wet cleaning method is that contaminants are being removed from the substrate, whereas another contaminants redeposited on substrate surface. For example, APM cleaning is extremely effective in removing particle and organic contaminant, but it allows metallic contaminants to redeposit on substrate surface wherever the APM (Ammonia-Peroxide Mixture) solution contains traces of metal ions [1]. HPM (Hydrochloric acid Peroxide Mixture) cleaning also suggested to remove the metal contaminants. However, it causes particle contaminants to redeposit on substrate surface because of electrostatic attraction. The zeta potential of particles is almost positive, whereas the zeta potential of Si surface is negative in acidic solution. Therefore, it is necessary to develop the HF based solutions instead of the conventional cleaning. HF/DIO3 and HF/organic acids were selected as cleaning solution. In this study, HF cleaning solutions were optimized to remove the metal contaminants from the substrate surface. Also mechanism of cleaning process and a theoretical understanding of metal growth are studied. The metal contaminants were removed by Si etching in HF/DIO3. The etching rate of Si is increased with increasing of DIO3 and HF concentrations. The organic acid and HF mixing solution does not oxidize the Si surface. Thus, the Si etch rate cannot be measured in HF/organic acid. So, silicon oxide substrates namely ALD and TEOS were used rather than silicon wafer. As a result, the organic acids do not affect the etching rate of SiO2. The metal removal efficiency was measured in various HF based solutions by using two different metals, namely Cu and Al. In high concentration of organic acid, the copper removal efficiency in HF/oxalic acid is higher than in HF/citric acid. In low concentration of organic acid, the copper removal efficiency in HF/citric acid is higher than in HF/oxalic acid. The aluminium removal efficiency is more than 90% in all cleaning conditions. The copper and aluminium removal efficiency is more than 90% in HF/DIO3, which has the lowest etch rate. Therefore, it was concluded that HF and organic acid were able to remove the metallic contaminant at optimized cleaning condition and also have high cleaning efficiency above 95% in HF/DIO3.