ABSTRACT Eddy current sensor (EC sensor) is a non‐destructive and non‐contact method to measure the thickness of metal coatings in real time. However, it is known that the distance between the EC sensor and the object to be measured (lift‐off) leads to thickness measurement errors in metal coating thickness measurement using the EC sensor. In this paper, we propose a simple method to measure the thickness of non‐magnetic metal thin films formed on ferromagnetic metal substrates using EC sensor in the sub‐micron order and to solve the lift‐off problem. Specifically, based on Dodd's theory, the measurement principle of the EC sensor is modeled theoretically, and the verification is conducted using an EC sensor designed based on the model and its driving circuit. According to the proposed method, the EC sensor shows high sensitivity in the range of Cu film thickness from 0.1 µm to 1.0 µm, which is about 400 to 500 times higher than the sensitivity due to lift‐off. This indicates that the effect of lift‐off can be minimized. A method for measuring the thickness of Cu films on the sub‐micron order at arbitrary lift‐off is also shown.
Matsuura et al. (Thu,) studied this question.