Evaluation Results of a new EUV Reticle Pod having Reticle Grounding Paths

摘要

A new SEMI standard El52-0709 "Mechanical Specification of EUV Pod for 150 mm EUVL Reticles" has been published in July 2009. In the standard, reticle grounding requirements are mentioned as related information: an electrical connection between the front and back sides of EUVL reticles as well as the electrical connection to the reticle backside from outside the outer pod may be needed and specified in future. Reticle grounding is very important for reticle protection not only from electrostatic discharge (ESD) damage but also from particle contamination due to electrostatic attraction (ESA). Many past data suggested that EUV masks have to be grounded during shipping, storage and tool handling to prevent particle adhesion. Canon, Nikon and Entegris have jointly developed a new ESD-free EUV pod "cnPod-ESD" which has electrical connections to the reticle from outside the outer pod by modifying a SEMI compliant EUV pod "cnPod". In order to have an electrical connection between the reticle backside and the outer pod, a cantilever is installed inside the inner pod cover. The cantilever touches the reticle backside just inside 146mm x 146mm which is specified as the minimum conductive layer area in SEMI P37 "Specification for Extreme Ultraviolet Lithography Substrates and Blanks". In order to have an electrical connection between the reticle frontside and the outer pod, though it is not required in El52, an electrical conductive material is used for the reticle supports on the inner pod baseplate. We will show various evaluation data of the new ESD-free pods from particle contamination point of view and will discuss the necessity of the reticle grounding in this paper. We will also mention the necessity of modification of the SEMI standard P37 to make a universal EUV ESD-free pod.