Faculty Publications
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Item Particle Removal by Surfactants During Semiconductor Cleaning(Elsevier, 2022) Yerriboina, N.P.; Park, J.-G.; Poddar, M.K.Particle removal during semiconductor processing is very crucial to meet the requirements of device reliability and yield. Several process steps are involved during semiconductor manufacturing, and cleaning steps are necessary before and after each processing step to make the wafer surface ready for the next process. As wafers may have different kinds of surfaces and particulate contaminants, the cleaning should be carefully optimized to provide the necessary physical forces and/or chemical forces. In this chapter, two major semiconductor processing steps are discussed for the application of surfactants in removing particles: wafer cleaning and PCMP (post-chemical mechanical planarization) cleaning. There are several issues or challenges to remove the particles from these processing steps. Surfactants play a critical role in preventing the redeposition of the particles during the cleaning process by modifying surfaces to have repulsive interaction forces between particles and wafer surfaces. Some typical surfactants used for the semiconductor cleaning process and their characteristics are discussed. Various mechanisms involved in particle removal by surfactants are explained. They also play an important role in Si wafer cleaning in controlling the etch rates by adsorbing on the wafer surface. A PCMP cleaning is necessary to remove the slurry particles attached to the different substrates (such as dielectrics, metals, III-V materials) after the CMP process. These particles are removed by adding suitable surfactants to the cleaning solutions. The role of surfactants in particle removal depends on the type of substrate. A variety of surfactants used for the PCMP cleaning process are also discussed. © 2022 Elsevier Inc. All rights reserved.Item Nanocatalyst-induced hydroxyl radical (·OH) slurry for tungsten CMP for next-generation semiconductor processing(Springer, 2020) Poddar, M.K.; Ryu, H.-Y.; Yerriboina, N.P.; Jeong, Y.-A.; Lee, J.-H.; Kim, T.-G.; Kim, J.-H.; Park, J.-D.; Lee, M.-G.; Park, C.-Y.; Han, S.-J.; Choi, J.-G.; Park, J.-G.Chemical mechanical polishing (CMP) is one of the important steps that involves during fabrication of semiconductor devices. This research highlights the importance of tungsten (W) polishing slurries consisting of a novel nonionic, heat-activated FeSi nanocatalyst on the performance of W chemical mechanical polishing. The results obtained from the polishing data showed a higher W removal rate of 5910 Å/min with a slurry consisting of FeSi nanocatalyst at a polishing temperature of 80 °C. The increase in W polishing rate using FeSi slurry was explained on the basis of formation of a thicker oxide layer (WO3) due to the interaction between the W surface and hydroxyl radicals (·OH) generated via the reaction between FeSi and hydrogen peroxide at 80 °C. Higher ·OH generation and increase in oxygen depth profile of W film were confirmed by UV–Vis spectrometer and AES analysis, respectively. Compared to Fe(NO3)3 catalyst, the slurry with FeSi showed a higher static etch rate at 80 °C. Potentiodynamic polarization results obtained using FeSi slurry showed thicker WO3 passivation layer as compared to the slurry with Fe(NO3)3. The increase in the polishing rate of W CMP using slurry with FeSi nanocatalyst can be essentially attributed to the generation of much stronger oxidant ·OH due to its increased catalytic effect at a high polishing temperature of 80 °C. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Item Comparative evaluation of organic contamination sources from roller and pencil type PVA brushes during the Post-CMP cleaning process(Elsevier Ltd, 2020) Lee, J.-H.; Poddar, M.K.; Han, K.-M.; Ryu, H.-Y.; Yerriboina, N.P.; Kim, T.-G.; Wada, Y.; Hamada, S.; Hiyama, H.; Park, J.-G.In post-CMP (chemical mechanical polishing) processing, the use of poly vinyl acetal (PVA) brushes to clean the wafer surface is one of the most effective and prominent techniques applied for the removal of CMP contaminants. Recently, organic contaminants induced in different types of PVA brushes during brush manufacturing have been drawing substantial research interest in CMP communities. In this study, investigated the root cause of these residual organic impurities in two different types of PVA brushes was investigated: roller and pencil type brushes. PVA roller brushes have a skin layer due to the brush molding process, but pencil-type PVA brushes do not have the skin layer. Extraction of organic impurities from both types of brushes was accomplished using an ultrasound-assisted technique at a sonication frequency of 40 kHz, and input power of 600 W. Further evaluation of these organic impurities using Field Emission Scanning Electron Microscopy (FE-SEM) revealed a large number of organic impurities in roller brushes and negligible impurities in pencil brushes. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed polydimethylsiloxane (PDMS) as the organic impurities extracted from PVA roller brushes, which were generated during the brush manufacturing process. The PDMS content in PVA roller brushes was further analyzed using FE-SEM micrographs via dissolving the organic impurities in tetramethylammonium hydroxide solution (TMAH). During brush fabrication, the high content of PDMS organic impurities in roller PVA brushes is essentially attributed to the presence of the additional skin layer formed by the mold releasing agent at the mold-cavity interface. © 2020 Elsevier LtdItem Tungsten passivation layer (WO3) formation mechanisms during chemical mechanical planarization in the presence of oxidizers(Elsevier B.V., 2021) Poddar, M.K.; Jalalzai, P.; Sahir, S.; Yerriboina, N.P.; Kim, T.-G.; Park, J.-G.Effects of single and mixed oxidants of Fe(NO3)3 and H2O2 containing acidic silica slurries were studied to investigate the mechanism of tungsten (W) chemical mechanical planarization (CMP). The W polishing rate obtained from the CMP test depicted high W polishing rate in the presence of mixed oxidants of Fe(NO3)3 and H2O2 as compared to a single oxidant of either H2O2 or Fe(NO3)3. The formation of a passive layer of tungsten oxide (WO3) and W dissolution could be the reason for these results as confirmed by XPS. Further investigation revealed that the generation of much stronger oxidants of hydroxyl radicals ([rad]OH) was solely responsible for WO3 layer formation. Quantitative evaluation of [rad]OH generation was estimated using a UV–visible spectrophotometer and confirmed that in-situ generation of hydroxyl radicals ([rad]OH) could be a main driving force for the high W polishing rate by converting a hard W film into a soft passive film of WO3. WO3 film formation was further confirmed using potentiodynamic polarization studies, which showed a smaller value of corrosion current density (Icorr) in mixed oxidants of Fe(NO3)3 and H2O2 as compared to the large values of Icorr observed for H2O2 alone. This study revealed that a single oxidizer of either Fe(NO3)3 or H2O2 was not capable of achieving a high W removal rate. Rather, only mixed oxidants of Fe(NO3)3 and H2O2 could cause a high W polishing rate due to excessive in-situ generation of [rad]OH radicals during the W CMP process. © 2020