Small Conductive Particle Detection with a Microwave Resonant Cavity

SUMMARYThe recent miniaturization and increased complexity of electrical devices have increased the influence of impurities on device performance, especially the influence of small conductive particles with a size on the order of micrometers. Therefore, the inspection of devices during the manufacturing process has become important. In this study, changes in the resonance properties of a microwave cavity were used to detect a metal particle. The decrease in the resonant frequency for a 100‐µm stainless steel sphere was about 0.1 MHz, which was less than 1 ppm of the resonant frequency used. This frequency change is too small to detect directly in the output of a particle detector. Transmission measurements (the scattering parameter S21) at a frequency that was a few megahertz higher than the resonant frequency where the S21 changes sharply were used to magnify signal changes resulting from the introduction of a small conductive particle. A resonant frequency of 13.3 GHz and a frequency 3 MHz higher were chosen for obtaining measurements in the present study. By applying a filtering technique, it was shown that the minimum detectable sphere size is around 50 µm. This sensitivity was