Multiple Layer CD Control Treatment

摘要

Tight control of intra-field CD variations becomes more and more important as the pattern sizes on wafer shrink. For intra-field CD uniformity improvement several techniques have been developed. A very effective method is changing the local mask blank transmittance according to measured Intra Field (IF) CD variations using Pixer's CDC? technique. This process is irreversible. For various practical reasons it would be helpful to have the opportunity for a second or more mask blank treatments. A first application could be to improve an unsatisfying CDU post first treatment. A second application can be the switch of the mask usage to another tool group. Furthermore, the opportunity to use multiple CDC treatments would allow the splitting of the correction process for the mask and the tool separately, whereas in a first correction only the mask CDU errors will be corrected and after the mask is supplied to the customer another correction may be required to reduce the exposure tool contributions to the CDU budget. Therefore the intention of the paper is to evaluate the opportunities of a Multiple CDC (MCDC) correction process, to determine its accuracy and the corresponding limits. To do this two CDC tool projection lenses have been characterized, which have been developed for different focus positions. We will characterize their transmittance transfer performance, stability and sensitivities. The required multiple layer distances will be determined. The linearity of the multiple CDC treatment will be analyzed using AIMS? measurements and wafer prints. We will present results of successful multiple CDC corrections for production masks.