Removing metallic contaminants from the photochemical supply chain is critical for the creation of high yielding, highly reliable semiconductors. Metallic contaminants may lead to various types of defects, such as cone defects, that can result in significant yield loss and degraded long-term reliability. This makes control of metallic contaminants even more critical in advanced photolithography processes, where the device reliability demands metal contaminants at parts per trillion (ppt) levels. Previous work3 demonstrated the ability of two purifiers, PurasolTM SP and SN, to reduce the metal contaminants in a variety of organic solvents. In this paper we will discuss our continued work to reduce contamination sources that can contribute to defect formation in photolithography applications.
Metal contaminants are notorious yield detractors throughout semiconductor unit processes. Metallic contaminants can create small, hard-to-detect defects that can eventually result in cone defects and gate leakage. Because these contaminants are so hard to detect, it is extremely difficult to pinpoint their root cause and identify opportunities to remove them. Clean photochemicals experience many contamination opportunities between their final quality control checks at the end of manufacturing and dispense onto a wafer. The complexity of the interactions of metal contaminants and the components in photochemicals is an important consideration when designing removal methods. This challenge increases when metaloxide photoresists are introduced into high volume manufacturing, whereby metals that enhance etch resistance must remain in the formulation, while specific metal contaminants must be removed. In this paper, we will describe different types of metal contaminants in photochemicals and raw materials, review how these contaminants are removed using membrane-based technologies, and define new methodologies to better target metal in photochemicals.
Metal ions in photoresists and solvents pose an ever greater contamination problem in photolithography’s advanced applications. The reduction of metal contaminants is critical in the entire photochemical supply chain. In this paper we demonstrate that two novel membrane purifiers dramatically reduced the metal contents in a range of organic solvents. These solvents are used for photoresist manufacturing and for wafer surface and dispense line rinse in track tools. The impact of flow rate and metal concentrations in the feed on the metal removal efficiency of the purifiers is presented. Furthermore, a study to determine the dominant mechanism of metal reduction in solvents is proposed.
Weak-polar solvents like PGMEA (Propylene Glycol Monomethyl Ether Acetate) or CHN (Cyclohexanone) are used to dissolve hydrophobic photo-resist polymers, which are challenging for traditional cleaning methods such as distillation, ion-exchange resins service or water-washing processes. This paper investigated two novel surface modifications to see their effectiveness at metal removal and to understand the mechanism. The experiments yielded effective purification methods for metal reduction, focusing on solvent polarities based on HSP (Hansen Solubility Parameters), and developing optimal purification strategies.
KEYWORDS: Lithography, Photoresist materials, Immersion lithography, Semiconducting wafers, Line width roughness, Line edge roughness, Scanning electron microscopy, Particles, Bridges, Finite element methods, Fermium, Frequency modulation
Specific “killer-defects”, such as micro-line-bridges are one of the key challenges in photolithography’s advanced applications, such as multi-pattern. These defects generate from several sources and are very difficult to eliminate. Pointof-use filtration (POU) plays a crucial role on the mitigation, or elimination, of such defects. Previous studies have demonstrated how the contribution of POU filtration could not be studied independently from photoresists design and track hardware settings. Specifically, we investigated how an effective combination of optimized photoresist, filtration rate, filtration pressure, membrane and device cleaning, and single and multilayer filter membranes at optimized pore size could modulate the occurrence of such defects [1, 2, 3 and 4]. However, the ultimate desired behavior for POU filtration is the selective retention of defect precursor molecules contained in commercially available photoresist. This optimal behavior can be achieved via customized membrane functionalization. Membrane functionalization provides additional non-sieving interactions which combined with efficient size exclusion can selectively capture certain defect precursors. The goal of this study is to provide a comprehensive assessment of membrane functionalization applied on an asymmetric ultra-high molecular weight polyethylene (UPE) membrane at different pore size. Defectivity transferred in a 45 nm line 55 nm space (45L/55S) pattern, created through 193 nm immersion (193i) lithography with a positive tone chemically amplified resist (PT-CAR), has been evaluated on organic under-layer coated wafers. Lithography performance, such as critical dimensions (CD), line width roughness (LWR) and focus energy matrix (FEM) is also assessed.
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