Method of layer thickness measurement

摘要

The layer thickness of an object including a substrate and a layer formed thereon is measured by the following steps. First, with regard to a reference system consisting of a reference substrate and a reference layer formed thereon, which are formed of the same materials as those of the object, and an ultrasonic wave propagation medium, the incident angle theta at which an ultrasonic wave is applied through the propagation medium to the reference layer and the product H of the frequency of the ultrasonic wave and the thickness of the reference layer are calculated, the incident angle theta and product H having such values as minimize the intensity of the ultrasonic wave reflected from the reference layer. The layer of the object is put in contact with the ultrasonic wave propagation medium, and an ultrasonic wave is applied to the layer through the propagation medium at the incident angle theta . Then, the frequency of the ultrasonic wave reflected from the layer is measured to detect the frequency of the incident ultrasonic wave for the minimum reflected wave intensity. The thickness of the layer of the object is calculated from the detected frequency and the value H.