Problem karlsuss2 SNF 2011-05-16 03:00:47: camera focus flickers during backside align

[vilanova at snf.stanford.edu]

We have checked the Top and Bottom Cameras and Exposed and 
Aligned  wafers , we couldnt  duplicate the flickering problem,
what we found was that One of the chuclks was dirty therefore we 
couldnt  get good vacuum , Cleaned the chuck and try again , Focus
Working fine and there was no vacuum Issue problem anymore, We'll
keep an eye to see if the problem comes back.