Process and equipment engineers are always seeking ways to improve yield quickly and efficiently, especially on newly developing processes. These engineers have many tools at their disposal – equipment enhancements, software upgrades, and materials improvements. Many of these tools come from OEMs (other equipment suppliers) and materials suppliers who all benefit from close collaboration with IDMs to improve yield. This paper will discuss the strategies utilized to improve yield on 32 nm BEOL (back end of line) lithography processes with sub-10 nm photochemical filtration. This collaboration generated electrical yield data that validated the performance of several sub-10 nm photochemical filters on various resist and ancillary chemicals used in a tri-layer stack. Examples of yield enhancement include the use of 5 nm UPE (ultra high molecular weight polyethylene) in OPL (optical planarizing layers) which showed a 69% improvement in overall median yield for an OPL material used in the first metallization layer, and a 26% improvement for a second OPL material used in subsequent metallization processes . In addition, this paper will present data studying pre-wetting of a 5 nm point-of-use filter before track installation. Building on the success of this collaboration, an example filtration roadmap is also explored to show the benefits of using advanced filtration in 32 nm technologies and beyond.
Many yield limiting, etch blocking defects are attributed to "flake" type contamination from the lithography process. The wafer edge bevel is a prime location for generation of this type of defect. Wafer bevel quality is not readily observed with top down or even most off axis inspection equipment. Not all chemistries are removed with one "universal" cleaning process. IC manufacturers must maximize usable silicon area as well. These requirements have made traditional chemical treatments to clean the wafer edge inadequate for many chemistry types used in 193nm processing. IBM has evaluated a method to create a robust wafer bevel and backside cleaning process. An August Technology AXi<sup>TM</sup> Series advanced macro inspection tool with E20<sup>TM</sup> edge inspection module has been used to check wafer bevel cleanliness. Process impact on the removal of post apply residues has been investigated. The new process used backside solvent rinse nozzles only and cleaned the wafer bevel completely. The use of the topside edge solvent clean nozzles was eliminated. Thickness, wet film defect measurements (wet FM), and pattern wafer defect monitors showed no difference between the new backside rinse edge bead removal process and the process of record. Solvent topside edge bead removal of both bottom anti-reflective coatings and resist materials showed better cut width control and uniformity. We conclude that the topside solvent edge bead removal nozzle can be removed from the process. Backside solvent rinse nozzles can clean the backside of the wafer, the wafer bevel, and can wrap to the front edge of the wafer to provide a uniform edge bead removal cut width that is not sensitive to coater module tolerances. Recommendations are made for changes to the typical preventive maintenance procedures.
Demands for continued defect reduction in 300mm IC manufacturing are driving process engineers to examine all aspects of the chemical apply process for improvement. Historically, the defect contribution from photoresist apply nozzles has been minimized through a carefully controlled process of "dummy dispenses" to keep the photoresist in the tip "fresh" and remove any solidified material, a preventive maintenance regime involving periodic cleaning or replacing of the nozzles, and reliance on a pool of solvent within the nozzle storage block to keep the photoresist from solidifying at the nozzle tip. The industry standard has worked well for the most part but has limitations in terms of cost effectiveness and absolute defect elimination. In this study, we investigate the direct washing of the chemical apply nozzle to reduce defects seen on the coated wafer. Data is presented on how the direct washing of the chemical dispense nozzle can be used to reduce coating related defects, reduce material costs from the reduction of "dummy dispense", and can reduce equipment downtime related to nozzle cleaning or replacement.