How To Detect Trace Metals During Semiconductor Manufacturing

APPLICATION BRIEF ICP - Mass Spectrometry AUTHOR Kyoko Kobayashi PerkinElmer Yokohama, Japan Metallic Impurity Analysis in Ultra-Pure N-Methyl Pyrrolidone with the NexION 5000 ICP-MS Introduction In recent years, as semiconductor devices have become smaller and more sophisticated, it has become essential to prevent metal contamination, which causes yield loss. Accordingly, strict impurity control is required for chemicals used in the fabrication process. A variety of organic solvents are used in the fabrication process, such as 2-propanol (IPA), 2-acetoxy-1-methoxypropane (PGMEA), 1-methoxy-2-propanol (PGME), and N-methyl-2-pyrrolidone (NMP). Among these, NMP is known as a polar solvent with very high solubility, in addition to being easy to handle due to its high boiling point and low freezing point. Because of this property, NMP is used as a typical stripper for photoresists. If metal in the stripper remains in the circuit pattern, this metal may affect the electrical and other characteristics of the semiconductor. Therefore, the NMP used must be of high purity. Inductively coupled plasma mass spectrometry (ICP-MS) is a highly sensitive quantitative method that can detect many elements on the order of ng/L (ppt) and pg/L (ppq), so it is commonly used as a control technique for elemental impurities in organic solvents and photoresists. In the past, generally, it was considered difficult to measure organic compounds, such as organic solvents and photoresists directly by ICP-MS. Therefore, such samples were acid-decomposed by nitric acid before measurement. This is due to the introduction of organic solvents, which are more volatile than aqueous solutions, and changes the state of the ion source (plasma) of the ICP-MS, making it difficult to maintain the plasma. However, this pretreatment process has the potential for contamination, which has been a problem for accurate impurity analysis. However, technologies employed by PerkinElmer, such as a free-running RF generator,1 have made it possible to maintain plasma even on samples containing difficult matrices, allowing organic solvents to be introduced directly into the plasma. This greatly reduces time-consuming preparation and contamination during acid digestion, enabling direct analysis of organic solvents, additionally organic-compounds analysis, such as photoresist, with simple dilution. www.perkinelmer.com Metallic Impurity Analysis in Ultra-Pure N-Methyl Pyrrolidone with the NexION 5000 ICP-MS However, the concentration of elemental impurities in commercial organic solvents has been raised as a challenge. As the required impurity levels decreased, the impurity concentrations of some elements in widely available, relatively pure organic solvents (e.g., electronics industry-grade) is high,2 and it has become a barrier for semiconductor-level analysis. The concentration of impurities in organic solvents is reflected in the background equivalent concentration (BEC) value, so, the BEC value must be improved to obtain a lower limit of quantitation. For this reason, many quality control (QC) laboratories use organic solvents that have been purified by distillation for ICP-MS analysis.3 However, this distillation process has the disadvantage of being time-consuming because it is performed below the boiling point of the organic solvent. Also, depending on the distillation environment and other factors, contamination may occur. In addition, when impurities in organic solvents are evaluated by direct introduction without pretreatment, such as acid digestion, it is important to completely remove spectral interferences caused by argon and carbon because blanks cannot be subtracted during the analysis. Therefore, ICP-MS is required to have higher interference removal capability. This application brief reports the results of analysis of 37 elements in ultra-pure NMP using the NexION® 5000 multi-quadrupole ICP-MS. Experimental Sample and Standard Preparation In this study, ultra-high-purity-grade Supreme Pure (SP)-NMP4 (FUJIFILM Wako Pure Chemicals Co., Ltd.) was used for analysis. A multi-element mixture standard solution (PerkinElmer) and a single-element standard solution (PerkinElmer) were used as standard solutions and added to the samples. Instrumentation A NexION 5000 multi-quadrupole ICP-MS was used for this measurement. The combination of the free-running RF generator and LumiCoil™ RF coil1 employed in the NexION 5000 provides robustness and high stability in organic solvent measurements. The second-generation Triple Cone Interface with OmniRing technology5 contributes to improved signal-to-background (S/B) ratios. In addition, the quadrupole in the Universal Cell (Q2) allows the use of reaction gases without dilution. Combined, these features enable the NexION 5000 to achieve outstanding BECs with excellent spectral interference removal. Instrument conditions are listed in Table 1. Reaction (DRC) mode using undiluted (100%) NH3, O2, H2, or mixtures of these gases is a very effective way for removing spectral interferences by changing interfering ions to non-ionic components or ions of different masses, or by producing cluster ions of the element of interest (mass shift). By using 100% reaction gas, a smaller amount of gas can be used to effectively remove interferences and produce cluster ions, and the quadrupole with the bandpass in the cell prevents the formation of new interferences (reaction byproducts). In MS/MS mode, Q1 and Q3 are set to the same mass, while in Mass Shift mode, the elements to be analyzed are measured as product ions with the reaction gas at a higher mass. Some elements without spectral interference are measured in Standard (STD) mode, where no gas flows in the cell. 2 Component/Parameter Description/Value Nebulizer PFA-100, Ultem probe, Free aspiration Sample Uptake ~ 100 μL/min Spray Chamber SilQ Cyclonic Torch One-Piece Quartz with 1.5 mm i.d. Injector Oxygen Gas for Plasma Around 5% of nebulizer gas PC3X Peltier Cooler 2°C Cones Pt-tip Sampler and Skimmer, Ni Hyper-Skimmer RF Power 1600 W (Hot Plasma), 900 W (Cold Plasma) Measuring Time/Isotope 1 sec Scan Modes MS/MS, Mass Shift, Q3 Only Cell Gases NH3 and O2 (all 100%) Table 1. Instrumental Parameters. Results and Discussion Table 2 shows BECs and limits of detection (LODs) from the SP-NMP analysis. By using the appropriate scan mode and profile (cell gas and plasma conditions) for each element, we were able to obtain BECs below ppt for all 37 elements measured. This demonstrates the effective spectral interference removal capability of the NexION 5000 and the outstanding quality of the ultra-pure NMP (SP-NMP). It is also noteworthy that good results were obtained in Na and Cu without distillation, which are often a particular problem in NMP for the electronics industry grade. Metallic Impurity Analysis in Ultra-Pure N-Methyl Pyrrolidone with the NexION 5000 ICP-MS Element Q1 Q3 Scan Mode Profile BEC (ng/L) LOD (ng/L) Li -- 7 Q3 Only STD Cold 0.018 0.0015 Na -- 23 Q3 Only STD Cold 0.57 0.015 Mg 24 24 MS/MS NH3 DRC Cold 0.11 0.016 Al 27 27 MS/MS NH3 DRC Cold 0.026 0.012 K 39 39 MS/MS NH3 DRC Cold 0.23 0.051 Ca 40 40 MS/MS NH3 DRC Cold 0.10 0.023 Ti 48 64 Mass Shift O2 DRC 0.018 0.032 V 51 51 MS/MS NH3 DRC 0.017 0.012 Cr 52 52 MS/MS NH3 DRC Cold 0.025 0.019 Mn 55 55 MS/MS NH3 DRC Cold 0.012 0.012 Fe 56 56 MS/MS NH3 DRC Cold 0.66 0.062 Co 59 59 MS/MS NH3 DRC Cold 0.0094 0.049 Ni 60 60 MS/MS NH3 DRC Cold 0.12 0.31 Cu 63 63 MS/MS STD 0.076 < 0.001 Zn 66 66 MS/MS NH3 DRC 0.56 0.83 Ga 71 71 MS/MS NH3 DRC 0.050 0.26 Ge 74 90 Mass Shift NH3 DRC 0.071 < 0.001 As 75 91 Mass Shift O2 DRC 0.046 0.24 Sr 88 88 MS/MS NH3 DRC 0.012 0.061 Zr 90 106 Mass Shift O2 DRC 0.0095 < 0.001 Nb 93 125 Mass Shift O2 DRC 0.0047 < 0.001 Mo 98 98 MS/MS NH3 DRC 0.020 0.10 Ru 101 101 MS/MS NH3 DRC 0.029 < 0.001 Pd 105 105 MS/MS STD 0.034 < 0.001 Ag 109 109 MS/MS NH3 DRC 0.055 0.29 Cd 111 111 MS/MS NH3 DRC 0.14 < 0.001 In 115 115 MS/MS NH3 DRC 0.007 0.017 Sn 120 120 MS/MS NH3 DRC Cold 0.16 0.36 Sb 121 121 MS/MS NH3 DRC 0.047 0.12 Te 130 130 MS/MS NH3 DRC 0.043 0.24 Ba -- 138 Q3 Only STD 0.0042 0.011 Hf -- 180 Q3 Only STD 0.0046 0.024 Ta -- 181 Q3 Only STD 0.0019 0.0097 W -- 182 Q3 Only STD 0.0094 0.049 Os -- 190 Q3 Only STD 0.012 0.061 Au 197 197 MS/MS NH3 DRC 0.069 < 0.001 Pb 208 208 MS/MS NH3 DRC 0.034 0.17 Table 2. BECs and LODs in the SP-NMP. Note: BECs lower than LODs are also shown in the table. Conclusion Equipped with the latest technologies, including proprietary multi-quadrupole technology, LumiCoil load coils, and a freerunning RF generator, the NexION 5000 ICP-MS demonstrated excellent trace analysis performance including superior spectral interference removal in organic solvent measurements. Acknowledgements We would like to express our sincere gratitude to FUJIFILM Wako Pure Chemicals Corporation for providing us with highly purified NMP for this study. References 1. Cheung T. S., et al., “Advantages of a Novel Plasma Generator for the NexION 1100/2200/5000 ICP-MS Systems” PerkinElmer Technical Note, 2024. 2. https://labchem-wako.fujifilm.com/us/category/00282.html (FUJIFILM Wako Pure Chemical Corporation Website) 3. Kobayashi K., et al., “Analysis of Metallic Impurities in Organic Solvents Used in IC Fabrication with the NexION 5000 ICP-MS” PerkinElmer Application Note, 2021. 4. https://biz.fujifilm.com/ffwkLP_SP-NMP_contact.html (FUJIFILM Wako Pure Chemical Corporation Website) 5. Badiei H., et al., "Advantages of a Novel Interface Design for the NexION 2200/5000 ICP-MS" PerkinElmer Technical Note, 2023. Component Description Part Number Nebulizer PFA-100 with Ultem Probe N8152594 Spray Chamber SilQ with AMS Gas Port N8152539 Peltier Cooler PC3X N8152382 Torch Quartz 1.5 mm One-Piece for Organics N8152616 Cones Pt Sampler N8161140 Pt Skimmer N8161041 Ni Hyper-Skimmer N8160120 Gas Line O2 N8152426 Multi-Element Standards Multi-Element Solution 3 without Mercury N9301720 Multi-Element Solution 4 N9300234 Multi-Element Solution 5 N9300235 Single‐Element Standard 100 µg/mL Osmium (Os) N9304383 Consumables Used For a complete listing of our global offices, visit www.perkinelmer.com/ContactUs Copyright ©2024, PerkinElmer U.S. LLC. All rights reserved. PerkinElmer® is a registered trademark of PerkinElmer U.S. LLC. All other trademarks are the property of their respective owners. 114081 PerkinElmer U.S. LLC 710 Bridgeport Ave. Shelton, CT 06484-4794 USA (+1) 855-726-9377 www.perkinelmer.com