A new tailored point-of-use filter to reduce immersion lithography downtime and defects

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 Oktolex TM 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.