Thin film forming apparatus, film thickness measuring method and film thickness sensor

Abstract

A technology which is capable of an accurate measurement of the film thickness even if an exfoliation occurs is provided. A difference frequency Δfis calculated from a resonance frequency fof a film thickness sensor at a current time aand a resonance frequency fat an immediate past time a, and whether the exfoliation has occurred or not is detected from its sign and a comparison result relative to a reference value. When the exfoliation has occurred, a corrected film thickness value T' is obtained by adding the thickness Δtof the exfoliation film to an increased film thickness value T which is determined from a resonance frequency fmeasured at a future time ato be converted to the thickness of a film on a film forming object, and whether the formation of the film should be terminated is judged in comparison to an aimed value. Thus, even if the exfoliation occurs in the film thickness sensor, the film thickness value of the thin film on the surface of the film forming object can be accurately obtained.