No abstract

ABSTRUCTIn mask making, ZEP7000 resist process with MEBES writing tool is widely adopted to produce advanced masks. This time, we tried to improve resist pattern CD uniformity in ZEP process using our special techiiiques. Resist sensitivity uniformity ofniask blank is one of the most significant parameters for resist pattern CD uniformity. In ZEP7000 coating process (coating, pre-baking and cooling), our original cooling method was adopted in consideration of its resist sensitivity properties. Resist filin thickness loss (RTL) uniformity during development was examined in order to analyze the resist sensitivity uniformity within a mask blank. It was clearly seen that resist pattern CD uniformity was related with RTL uniformity. As for our original cooling method, an optimum cooling condition was easily obtained because it had only two parameters. As the results, RTL uniformity was 2.4nm (range), moreover, resist pattern CD uniformity was l5nm (range) with the optimum cooling condition. RTL uniformity and resist pattern CD uniformity were also examined using blanks which were commercially available from two vendors. And these results were compared with the results of our original cooling method. Based on the results ofour study, we confirmed that our original cooling method was very effective for improvement of resist pattern CD uniformity on ZEP process.

This paper describes the study on overlay accuracy of reticles, using a reticle set for DRAM. It is found that single reticle pattern placement has to be higher accuracy than overlay of reticles, which may be a majority in the total overlay accuracy. Concerning some points of a reticle set, we found that there is a very large value. To match overlay accuracy of reticles with the demand of devices, we have shown that the suitable reticle exposure system has to be used and managed exactly. In order to assure overlay accuracy of a reticle set, it was proposed that single reticle pattern placement accuracy must be higher than overlay accuracy demand and the overlay accuracy yield also should be shown in some cases.

Cleaning is one ofthe most important processes in mask making, because it decides final quality In cleaning process, it is necessary for reticle cleanliness to not only remove particles from reticle but also prevent adsorption and re-deposition onto reticle. There is the knack for reticle cleaning, and we introduce three keys in this paper. The first key is the nnse after chemical treatment. By the rinse sequence modification, the cleaner was refined and the particle removal abifity was improved. The second key is quality control to grasp the situation of cleaner. By the daily check, cleaner's abnormal condition is found at an early stage, quick action is taken, and then stable cleaning quality is kept every day. And the third key is proper choice of cleaners. We have adopted precleaning process and selected the adequate cleaner for each cleaning level and improved cleaning yield and quality.

In this report, origins of CD error caused through Cr dry etching were investigated and some process conditions were evaluated for the advanced reticle productions. It is shown that resist patterns of ZEP-7000 written with MEBES-4500 showed a little CD deviation between the sparse and dense regions. These errors could be easily emphasized after Cr dry etching. Some dry etching conditions were examined and improvements were confirmed after the addition of etching assist gas and adequate intensity of AC magnetic field of MERIE (Magnetically Enhanced Reactive Ion Etching) system. It is also shown that resist profiles after development play important role in the CD distribution after dry etching for the reticle contained both sparse and dense region on the same plate. With our conventional condition, resist profile of ZEP-7000 showed a gentle slope after development. It is proved that this lower pattern contrast makes the Cr CD difference due to pattern loading much worse. Minimum CD error could be obtained through the process that made resist profile almost vertical. These results imply that total adjustments, not only for dry etching conditions but also for resist process that gives us the highest pattern contrast, are needed to solve the complex issues for the advanced CD control.