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.
Nanoscale patterning defects continue to challenge yield performance of photolithographic processes. It is well known that applying point-of-use (POU) filtration to patterning chemistries is effective for defect reduction. While POU filtration can remove contaminants from process chemistries, the filter materials of construction could adversely interact with the chemistry, resulting in a long filter flushing time or poor lithographic performance. Historically, the most common materials used to manufacture filters for POU photochemical filtration are ultrahigh molecular weight polyethylene (UPE) and Nylon. UPE membranes have outstanding chemical compatibility and enable sub-5 nm filtration, but can struggle to quickly reach baseline defectivity when trying to remove air from the smallest available pores. Nylon membranes provide additional non-sieving retention capabilities that can be instrumental in reducing wafer level defects without further reducing membrane pore size, but are not compatible with acidic chemistries.
To address the demand for new chemistry compatibility, reduced defectivity and increased productivity, Entegris has tailored a membrane as part of its OktolexTM family of technologies to address demanding lithography defectivity performance targets. The new membrane is cleaner, more retentive, and has an enhanced non-sieving particle capture capability when compared to a standard Nylon membranes. In an evaluation of the newly developed membrane using 45nm line/space patterning, the new membrane significantly outperformed both UPE and Nylon filters in microbridging defectivity. In addition, the new membrane also achieved baseline significantly faster than the other filters.
Advanced lithography techniques relying on innovations in scanner, track, and material technologies have been a consistent driver of Moore’s Law. As these innovations transition from laboratories to factories, all members of the lithography value chain must adapt. Filtration technology has relied upon a subset of carefully matched materials to filter lithographic materials. The introduction of new materials for emerging lithography techniques creates the opportunity to seek alternatives to ultra-high molecular weight polyethylene (UPE), Nylon, and polypropylene.
Fluoropolymers, such as polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkane (PFA), have been used widely in the fab to filter chemistries that require instant surface wettability and high flow rates. These requirements now align more closely with today’s leading-edge lithography materials. After a review of the motivation behind choosing new filtration materials in the lithography sector, this paper will identify the critical material attributes, specific design considerations, and the importance of membrane surface technologies, beginning in the photoresist manufacturing process. Data presented will include laboratory studies of fluoropolymer membranes in common solvents, on-wafer defect data, and bulk filtration manufacturing data, all showing the match between fluoropolymer filters and photolithography materials.
Negative tone development (NTD) has dramatically gained popularity in 193 nm dry and immersion lithography, due to their superior imaging performance [1, 2 and 3].
Popular negative tone developers are organic solvents such as n- butyl acetate (n-BA), aliphatic ketones, or high-density alcohols such as Methyl Isobutyl Carbinol (MIBC). In this work, a comparative study between ultra-high molecular weight polyethylene (UPE) and polytetrafluoroethylene (PTFE) POU filtration for n-BA based NTD has been carried out.
Results correlate with the occurrence or the mitigation of micro bridges in a 45 nm dense line pattern created through immersion lithography as a function of POU membrane.
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