Vacuum chuck for clamping workpieces, measuring devices and method for checking workpieces, in particular wafers

A method for checking a workpiece, with a measuring device having X-ray fluorescent radiation, the measuring device having a moveable measuring table for receiving the workpiece, wherein a primary X-ray radiation produced by a radiation source is aimed at the workpiece, and emitted secondary radiation is detected by a detector, and measuring signals detected by the detector are evaluated by way of a control device, wherein a vacuum chuck is provided on the moveable measuring table, the vacuum chuck having a clamping plate having a support surface, having at least one suction connection arranged on a base body for connecting to a negative-pressure device and for clamping the workpiece on the clamping plate by way of negative pressure which is received by the base body and having several suction grooves arranged in the clamping plate and are open towards the support surface, the support surface has several concentric suction grooves having at least one suction opening to which a negative-pressure line is connected or which is connected to a work channel, wherein every suction groove has a separate negative pressure, which is separate to the adjacent suction groove, is selectively controlled by way of at least one control valve by a control for supplying the respective negative pressure in the respective suction groove, and wherein lifting pins are provided opposite the support surface of the clamping plate, the method comprising:

• before fitting the vacuum chuck with the workpiece, the lifting pins opposite the support surface of the clamping plate are transferred into an extended position,
• placing the workpiece to be checked on the lifting pins by a handling device,
• supplying the lifting pins with negative pressure and the workpiece to be checked is fixed to them,
• transferring the lifting pins into a retracted position and the workpiece is placed on the support surface,
• selecting at least one of the sizes of the workpiece in the control, which causes the control to supply the corresponding suction groove with negative pressure and the workpiece is fixed on the support surface,
• checking the workpiece by way of X-ray fluorescent radiation,
• switching off the negative pressure in the at least one suction groove,
• transferring the lifting pins into the extended position,
• grasping the workpiece by the handling device, and
• switching off the negative pressure applied to the lifting pins and guiding the workpiece out of the measuring device by the handling device.