Evaluation of transfer of particles from dual-pod base plate to EUV mask

Since 2005, Canon, Nikon, and Entegris have been jointly developing an EUV mask carrier based on the "Dual Pod" concept in place of a pellicle. By using our MIRAI-Selete Mask Protection Engineering (MPE) tool, a few prototypes were tested for performance of particle protection in the case of both mask shipping and its handling in vacuum. As a result, the fundamental mechanical specifications of the Dual pod were registered as those of SEMI "E152" of an EUV Pod used in EUV mask. It is found that the latest pod named "cnPod", which is based on the SEMI E152, performs almost satisfactorily. Although superior protection performance with respect to external particles has been confirmed, the performance with respect to internal particles laid on the base plate of an inner pod is still under investigation. Therefore, we evaluate the influence of the internal particles laid on the base-plate surface for the first time. In order to confirm whether the particles on the base plate are transferred to the mask-patterned surface, well-characterized particles are dispersed on the base-plate surface. By using this contaminated base plate and the MPE tool, mask handling experiments are conducted. Under our experimental conditions, it is found that the number of test particles transferred to the mask surface is very low compared to the total number of particles on the base-plate surface.