A ring chuck that holds a wafer with a vacuum uses a vacuum trough that contacts the entire outer edge of the wafer. The chuck has a base having a top surface equal to or slightly smaller than a wafer to be tested with vacuum channels in the base. The base provides the mechanism to connect the chuck...http://www.google.se/patents/US20020024174?utm_source=gb-gplus-sharePatent US20020024174 - Ring chuck to hold 200 and 300 mm wafer
