Demands for continued defect reduction in 300mm IC manufacturing is driving process engineers to examine all aspects of the apply process for improvement. Process engineers, and their respective tool sets, are required to process films at temperatures above the boiling point of the casting solvents. This can potentially lead to the sublimation of the film chemical components. The current methods used to minimize wafer defectivity due to bake residues include frequent cleaning of bake plate modules and surrounding equipment, process optimization, and hardware improvements until more robust chemistries are available. IBM has evaluated the Tokyo Electron CLEAN TRACK<sup>TM</sup> ACT<sup>TM</sup> 12 high exhaust high temperature hotplate (HHP) lid to minimize wafer level contamination due to the outgasing of a bottom anti-reflective coating (BARC) films during the high temperature bake process. Goal was to minimize airborne contamination (particles in free space), reduce hotplate contamination build up, and ultimately reduce defects on the wafer. This evaluation was performed on a 193nm BARC material. Evaluation data included visual hardware inspections, airborne particle counting, relative thickness build up measurements on hotplate lids, wafer level defect measurements, and electrical open fail rate. Film coat thickness mean and uniformity were also checked to compare the high exhaust HHP with the standard HHP lid. Chemical analysis of the HHP module residue was performed to identify the source material. The work will quantify potential cost savings achieved by reducing added wafer defects during processing and extending PM frequency for equipment cleaning.
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.
Barometric pressure variations are known to affect the coating process resulting in photo resist film thickness variations in lithography track coat processes. The results of an internal TEL evaluation showed a strong correlation between barometric pressure variations and photo resist film thickness variations (as shown in introduction section). Based on those results, a "Barometric pressure compensation system" was developed to estimate and automatically correct for potential film thickness variations which would otherwise result from barometric pressure variations. An Inline system installed on a photo resist track at IBM was used to gather data for a variety of resist systems. A strong correlation was observed between barometric pressure variations and film thickness variations, and the effectiveness of automatic correction for this effect was demonstrated. In the case of KrF Escap-type resists (Resist A), the film thickness and barometric pressure are expressed in a primary approximate expression; the slope is -0.11nm/hPa, and the correlation coefficient (R<sup>2</sup>) is 0.93. As for the case of KrF Acetal-type resists (Resist B), the slope is -0.12 nm/hPa, and the correlation coefficient (R<sup>2</sup>) is 0.89. Through the use of the "Barometric pressure compensation system," photo resist film thickness variations were reduced from 2.7 nm (daily coating processed by the same recipe) to 0.6 nm for Resist A and from 5.0 nm to 1.4 nm for Resist B. The studies conducted showed that the "Barometric pressure compensation system" provides significantly improved photo resist film thickness control during variations in barometric pressure, and demonstrated that the technique can be applied effectively to a variety of photo resist materials.