MTI Instruments is a worldwide supplier of precision non contact physical measurement equipment with systems specifically designed for the PV industry.

PV 1000 Measurement Module
High-speed Thickness and Resistivity
Measurement System for
Photovoltaic Wafer Production

Using MTII's exclusive Push/Pull capacitance probe technology, each PV-1000 module provides up to three pairs of probes for measurement of maximum, minimum and average thickness, as well as total thickness variation (TTV) and wafer bow. plus optional resistivity measurements, or just resistivity measurements !.
For applications requiring additional channels, multiple PV-1000 modules can be chained together for unlimited line scans on the wafer.

Wafer saw mark detection and classification is accomplished by adding optional laser sensors to the PV-1000 module. Utilizing up to two of MTII's industry leading Microtrak - SA standalone laser heads, saw marks can be classified for orientation and depth simultaneously with wafer thickness scanning making the PV-1000 ideal for incoming wafer characterization and sorting.

Integrated data acquisition and control electronics analyze and transmit wafer data via the on-board Ethernet port at speeds of up to five wafers per second. The digital I/O port allows communication with wafer handling equipment for up to 64 classes of wafer sorting and binning. Remote monitoring capabilities allow you to see your production line data across your network or directly at the module.

MTI Instruments wrote an excellent application note about the capacitance measurement technique which you could find by clicking on Capacitance Measurement or look for additional application notes at http://www.mtiinstruments.com/products/semiconductormetrology.aspx