Ring chuck to hold 200 and 300 mm wafer

Abstract

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 to a measurement instrument and a vacuum source. An annulus of non-contaminant material that has a plurality of concentric rings extending upward from its outer edge is fixed to the base top surface with the trough between the concentric rings connected to the vacuum channels. The vacuum trough holds the wafer securely to the chuck and minimizes vibrations when the wafer is rotated. When the plurality of concentric rings are contained within the wafer exclusion band, the print through onto the tested area is minimized. The tops of the concentric rings are minimally elevated from the top surface of the base and form a sealed volume that supports the interior portion of the wafer. The tops are also made very narrow to allow small deformations, minimize contamination of the wafer and restrict the transfer of particles between the chuck and the wafer. In addition, the narrow rings limit the number of particles already on the backside of the wafer that are forced onto the wafer. The consistent support provided by the ring chuck simplifies modeling of the chuck/wafer system under rotation, improving the ability to remove the instrument signature from measurements.