Patent ID: 8546760

Claim:
An apparatus for checking thickness dimensions of semiconductor wafers during the machining on a grinding machine, including: a detection system with a light source in the infrared band, a detector of reflected beams and an optical probe, said light source and said detector being connected to the optical probe for emitting infrared beams along a longitudinal path towards a first surface of the wafer being machined and for receiving, substantially along said longitudinal path, beams reflected by said first surface and by at least one different surface defined by the wafer being machined; a control and processing unit connected to the detection system; and a support and positioning element for the optical probe including hydraulic ducts that are connected to an external source of a liquid and are adapted to generate a cushion of liquid in laminar flow between the optical probe and said first surface of the wafer being machined, said longitudinal path including said liquid cushion, said hydraulic ducts including an entry opening and a plurality of internal channels radially arranged with respect to said longitudinal path and communicating with an axial exit hole which is adapted to be arranged facing said first surface of the wafer, to generate said cushion of liquid in laminar flow.