Clean mask shipping module development and demonstration for EUVL masks and blanks

As semiconductor technology nodes continue shrinking down to 45nm and below, the requirements for number of particle adders and their size during optical mask blank shipment are getting tighter and tighter. In the case of extreme ultra-violet lithography (EUVL) for 32nm and below technology nodes, the requirements for shipping the final mask product are even more stringent. It virtually requires zero particle adders or single digit particle adders (if local mask clean tool is equipped at wafer fab) at 30nm size for 32nm technology node and even smaller size for the 22nm technology node. This EUVL mask handling specific issue is due to the lack of pellicle material available at EUV wavelength, because of strong EUV light absorption by all solid materials. In the past few years, several benchmarking studies on mask handling and shipping without pellicles have been conducted by different companies. The results indicated that many improvements are needed to bring down the handling and shipping induced particle adders at the required 30nm size for the 32nm technology node. In this study, we have evaluated particle generation at ≥60nm PSL equivalent size during mask shipment. We have demonstrated zero particle adders in shipping by using mask carriers with simple design. Our study included different commercially available carriers and non-commercially available carrier with designs to further minimize the particle generation and deposition onto the mask critical surface. The study has also shown that both the carrier design and the shipping packaging are responsible for clean mask transportation. The smallest particle size (60nm) evaluated in this study is limited by the metrology capability. Further evaluation for particle adders at size ≤60nm requires new development for higher sensitivity inspection capability.