The thickness of a sample is commonly measured by a Capacitive Thickness gauge. The measurement technique follows directly from the formula for capacitance. The capacitance of two parallel plates, separated by air, is directly proportional to the area of the plates and inversely proportional to the distance between the plates.
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When measuring the thickness of a silicon wafer, as in the RT-110, wafer acts as one plate of the capacitor, and a measurment electrode, held a fixed distance above the bottom surface of the wafer, acts as the second plate. Because the silicon in conductive, the thicker the wafer, the smaller the spacing between the “lower” plate and the upper plate.
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