| Popis: |
Reticle damage due to ESD is a well-known phenomenon.. A defective reticle prints defective dies1. Unfortunately, ESD damage to reticles is a common problem and becoming more common as time goes on. We have developed a diagnostic tool called the Canary Reticle for the purpose oflocating the sources of ESD damage within a photo bay. Over the past year, we have used it to study the effects of ESD on reticles. In this article, we summarize the findings ofthe study2. Extremely high levels of electrostatic charge develops in cleanrooms in general and particularly so for semiconductor cleanrooms. The absence of surface contamination, the action ofihe HEPA filters in sweeping ions out ofthe room and low humidity results in much higher voltage levels on objects as compared to conventional rooms. Many ofthe objects used must be excellent insulators or are insulators, but have been selected for other physical properties. Examples are quartz reticles and Teflon wafer cassettes and plastic reticle pods. The chrome structures on reticles have sharp corners, which concentrate the electric fields, making breakdown ofthe air between them easy to occur. The voltage on a conductor is the same at all points. Thus, in the presence of a voltage gradient (Electric field), the potential differences are focused into the gaps between the chrome structures, again making discharge easy. It is hoped that by understanding the mechanisms for ESD damage photo engineers will better be able to avoid it. |
