The invention relates to an apparatus and method for measuring thickness
and deviations from the thickness of very thin conductive coatings on
various non-conductive substrates, or of very thin non-conductive coatings
on conductive substrates. The apparatus consists of an inductive coil
having specific parameters, an external AC generator operating on
frequencies, e.g., from 50 MHz to 2.5 GHz, preferably from 100 MHz to 200
MHz, and a measuring instrument, such as an oscilloscope, voltmeter, etc.
for measuring output of the sensor. The coil has miniature dimensions. The
invention is based on the principle that inductive coil of the sensor,
active resistance of the coil winding, inherent capacitance of the
inductive coil (or a separate capacitor built into the sensor's circuit),
and the aforementioned AC generator form a parallel oscillating circuit.
The apparatus operates on very high resonance frequencies, preferably
within the range of 100 to 200 MHz, at which a capacitive coupling is
established between the coil of the oscillating circuit and the thin films
being measured. By measuring the parameters of the resonance oscillating
circuit, it becomes possible to measure film thickness below 500
Angstroms.
