Patent ID: 9508578
Filing Date: 2016-11-29
CPC Classification: G01F,H01L

Claim Text:
1. An apparatus comprising: a chuck having a top surface and configured to clamp a substrate to said top surface, said chuck having one or more recessed regions in said top surface, said recessed regions configured to allow a cooling gas to contact a backside of said substrate; a cooling gas inlet and a cooling gas outlet connected to said one or more recessed regions; a first measurement device connected to said cooling gas inlet and configured to measure a first amount of cooling gas entering said cooling gas inlet; a second measurement device connected to said cooling gas outlet and configured to measure a second amount of cooling gas exiting from said cooling gas outlet; and a controller configured to determine a difference between said first amount of cooling gas and said second amount of cooling gas, wherein said cooling gas comprises helium, neon, argon, or nitrogen.