Measurements of dielectric properties and dielectric film thickness using fringe-effect sensors and sensor arrays

Parallel-plate method is a gold standard for measuring dielectric properties of material under testing (MUT). However, it is less suitable for real-time, dynamic, and in-situ measurements. The alternative to the parallel-plate method is to use a planar interdigitated electrode array, fringe-effect (FE) sensor. However, interpretation of the FE sensor measurements is not easy due to the spatial nonuniformity of the electric excitation field created by the FE sensor and the extraneous contributions from the sensor substrate and unknown stray elements.; For quantitative dielectric measurements using FE sensors, two novel methods are proposed. The first method is based on the theoretical correlation between the impedance measurements obtained with the FE sensor and the dielectric properties of the MUT. The second method is supported by the theoretical model developed from the electroquasistatic form of Maxwell's equations. The dielectric measurement results of both methods are compared with those obtained using the parallel-plate measurements and show excellent agreement.; In order to measure the thickness of dielectric film under testing (FUT), several known methods based on different physical principles are available. However, most of those methods are limited to certain types of films and have difficulties in carrying out in-situ and on-line measurements. There are at least three advantages in using FE sensors to measure the thickness of FUT: First, the FE sensors have a planar structure that needs the access to only one side of dielectric FUT, which enables noninvasive and real-time measurements. Second, with the availability of modern microfabrication techniques, the FE sensors can be miniaturized into sub-mum range that allows for the placement of the FE sensors inside the process and laboratory equipments for the dynamic and in-situ measurements. Third, the FE sensors are much more economical than the other techniques. To obtain the FUT thickness from the FE sensor measurements; a novel method is proposed. For the quantitative verification of the proposed method, two types of FE sensors are used: the commercially available FE sensor, MS-01, and the custom-made FE sensor array consisting of three FE sensors of different interelectrode spacing. The thickness measurement results of each FE sensor are compared with the independently measured thickness results. The comparison demonstrates the excellent efficacy of the proposed method for the measurement of FUT thickness with the FE sensors when the thickness is less than a certain value, which is defined as the maximum estimable thickness of FE sensor equal to two third of the distance between two adjacent electrodes.