Patent ID: 6809542
Filing Date: 2004-10-26
Classification: G01N,G01R

Abstract:
Apparatus for non-contact determination of wafer resistance of a semi-conductor wafer, comprising:a first sensor element, separated from a surface of said wafer by a first air gap, for capacitively coupling an AC drive signal into a portion of said wafer; a second sensor element, separated from the surface of said wafer by a second air gap, for capacitively coupling an AC output signal out of said wafer portion, said AC output signal being produced by the drive signal flowing through a resistance of said wafer portion; an inductor in series connection with at least one of said first sensor element and said second sensor element; and means for automatically tuning a frequency of the AC drive signal to a resonant frequency at which capacitance impedance of the first air gap and of the second air gap is cancelled by inductive impedance of the inductor.