抄録
An overview of the present status of synchrotron radiation-based x-ray lithography (SRL) and its extendibility down to 0.1-micron features and lower are described. The attained performance of SR sources, aligners, and masks is measured with requirements for 1Gb DRAM level. Some of SR sources so far developed can provide enough SR flux for practicable throughput. While several prototype aligners have demonstrated sufficiently high alignment accuracy, the mask pattern placement needs to be further improved in order to fulfill the overlay requirement. The resolution well below 0.1micron is feasible with narrow proximity gap of order of 10micron. Difficulties in fabricating fine pattern masks can be reduced by making use of the phase shift effect. Investigation on the mask membrane deformation during stepping with the narrow proximity gap is now in progress. The present status of SRL and its possibility down to 0.1-micron features have been described. The key issues in 180nm dimensional region are improvement of pattern placement accuracy of masks and development of high throughput aligners. In order to upgrade SRL to a production-viable level, it will be necessary to optimize the whole SRL system. From this point of view, throughput is a good measure, since almost all components of SRL system relate with it. Another important issue is further improvement of the reliability. The SRL system is considered to be cost-effective only when many aligners are operated with single SR source. Thus, extremely high reliability is required of the SR source. This can be accomplished by establishing proper maintenance schemes based on accumulated data on operation, maintenance, and troubles at existing SR facilities routinely operating. Technical problems associated with fine pattern replication of order of 0.1micron have been also discussed. The possible solutions presented will lead to the extendibility over several generations of ULSI.
