Immersion topcoat and resist material improvement study by using immersion scanner

Abstract

ArF (193nm) immersion lithography is considered as the most promising next generation technology and significant effort to establish the immersion process for semiconductor device HVM is currently focused on the tool, material and process development. Immersion lithography enables the design of hyper numerical aperture (NA>1) lens systems by filling the gap between lens and resist with an immersion medium. Water is the ideal medium for 193nm immersion lithography and the water immersion system could reach up to 1.3 NA, giving higher resolution capability. There are several immersion specific requirements such as scanning properties and leaching characteristics. High speed scanning is necessary for mass production, so the water has to follow the lens and move on the resist film at considerably high speed.Direct water contact with resist film can cause the leaching of some resist components e.g. PAG. This leaching phenomenon could cause lithographic performance degradation and lens damage. Leaching and scanning phenomena are quite complicated and difficult to estimate the amount exactly with chemical analysis tools, so it is important to check the lithographic performance and scanning capability with a real immersion scanner. We have done many immersion experiments on various resists and top-coat materials using a Nikon immersion scanner (EET: Engineering Evaluation Tool). From the results, it was found that the properties of topcoat materials were closely related with immersion characteristics, such as scanning speed and defect formation. Specifically, defectivity evaluation results revealed that PAG leaching suppression was important for not only preventing lens damage but also reducing defect formation in the immersion process.

Advances in Patterning Materials for 193 nm Immersion Lithography

“…Many researchers have attempted to correlate immersion defectivity with some easily measured property of topcoat materials. In general, defectivity has found to decrease with increasing SRCA. ,,,, For example, Nikon showed that defectivity was markedly reduced with topcoats having receding water contact angles near 70° (Figure ) . This transition from high to low defectivity occurs above the critical velocity for film pulling (∼50°−60°) discussed previously .…”

“…Many experimental techniques have been devised to measure the kinetics of resist component extraction by water in order to meet these specifications. These techniques include simple contact of the resist surface to water confined in an O-ring or vial, flowing water through a specifically designed cell mounted on the wafer, or dragging a drop or puddle of fluid across the resist-coated wafer. ,,,− In an attempt to standardize leaching measurements, many vendors now utilize a dynamic method employing a multichannel flow cell (so-called dynamic WEXA)…”

Improvement of watermark defect in immersion lithography: mechanism of watermark defect formation and its reduction by using alkaline-soluble immersion topcoat

“…Application of these topcoats could make most of dry-photoresist usable in immersion process. Additionally, good scanning property of topcoat led to fewer defects because of fewer remaining water droplets 12 . In order to suppress watermark defect completely, preventing water penetration into topcoat film is important as well.…”