MEASURING METHOD OF FILM THICKNESS AND APPARATUS THEREFOR

PURPOSE:To enable measurement of the amount of adsorption of a substance and a film thickness with high accuracy by detecting a change in the cycle of vibration of a vibrating element or the cycle of a frequency-divided wave. CONSTITUTION:A vibration frequency of a vibrating element for measurement and an oscillator 1, which is f0 at first, changes by DELTAf with the adsorption of a substance on the vibrating element for measurement, and a frequency f0 - DELTAf is outputted. In an oscillator 2 for reference, a signal of a frequency fr is generated separately from the oscillator 1. The frequencies of the oscillators 1 and 2 are mixed in a mixer 3, subsequently, and an output of a frequency f1 is obtained from the mixer 3. Moreover, the output frequency f1 of the mixer 3 is frequency-divided into a frequency of 1/100, for instance, in a frequency-divider circuit 4, and an output f2 from the circuit 4 is turned into a gate pulse Pg of about 0.1 second by a gate pulse generating circuit 5. This pulse Pg and a reference pulse Ps generated from a reference oscillator 6 are inputted to an AND circuit 7, a pulse train Pg X Ps is outputted from the circuit 7 to a counter circuit 8 and a count train is counted. The result of counting is displayed in the circuit 8 and a film thickness is computed in a computer 9.