Improving CDs on a MEBES system by improving the ZEP 7000 development and dry etch process

Abstract

Previous papers have examined the use of ZEP 7000 resist with dry etch and the compatibility of this process with advanced MEBES writing tools. 1,2,3 This paper details further advances made to this process and the improvements in critical dimension (CD) control that can be made by fine-tuning the process. This paper describes how isofocal dose is found experimentally and how a process is established using that dose. The advantage of running a process at or near isofocal 4,5 is that it provides minimum CD variation. One disadvantage of running at isofocal is that data bias is usually required. With a higher dose than 8 μC/cm 2 , a new developer solvent from Nippon Zeon (ZED 750) is introduced to have a sufficient number of puddles and a long enough develop time to ensure good uniformity. Results of edge slope (i.e., sidewall profile) comparisons, resolution, and CD uniformity when using this process are presented and compared with results of the established process. Dry etching masks becomes increasingly important as the dimensions on the mask shrink in accordance with the SIA roadmap. The advantage of dry etch over wet etch is its anisotropy and, thus, a much reduced etch CD bias. One disadvantage of dry etch is the resist loss that occurs during plasma etching. The minimal resist thickness required for a dry etch process tends to be larger than that for wet etch. By choosing a different etch chemistry, significant improvements can be made in the selectivity during the dry etch, which is the ratio of the chrome etch rate relative to the ZEP 7000 resist etch rate. Improvements in selectivity may permit the use of thinner resists, resulting in a more robust process. Along with improved selectivity, the etch CD bias is decreased. This reduces the need to bias the data. Results from this alternative chemistry are shown.