PURPOSE: To measure the film thickness of a film which is thin as compared with wavelength in a short time without any mechanical scan by determining the combination of materials of the substrate and substrate of a body to be measured, and determining liquid for ultrasonic-wave propagation, and then irradiating an ultrasonic wave at an angle of incidence characteristic to them and finding the frequency at which the reflection factor is minimum.
CONSTITUTION: The liquid 4 for propagation is positioned on the body 1 to be measured, i.e. body consisting of the base plate 2 and film 3 formed thereupon, and ultrasonic wave generator and receivers, i.e. piezoelectric transducers 5 are provided above them to constitute a measurement system. On the other hand, the reflection factor to the ultrasonic wave incident at the angle characteristic to the combination of materials is minimum when the ratio of the film thickness and wavelength is a value characteristic to the combination of the materials. Namely, the reflection factor is minimum when d/λ=H or when d.f=C.H, where C, λ, (f), and (d) are the sound velocity in the liquid, wavelength, frequency, and film thickness and H is the ratio characteristic to the combination of the materials. This is utilized to measure the wavelength of an ultrasonic wave whose reflected wave decreases in intensity and the film thickness is calculated from said equation.
TAKEUCHI EIJI
HAYASHI EISAKU
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