Comparative Study of Four-Point Measurements of Copper Thin Films Resistivity in Aligned and Square Configuration at Low Frequencies

Abstract

The main objective of this research work is the comparison of the two Van Der Pauw four-point measurement configurations (aligned and square) commonly used to measure the resistivity of metal thin films which are widely used in the manufacture of planar components such as inductors, transformers, insulators, circulators, etc. Electrical characterization is very important because it ensures the quality of the metal supposed to conduct electrical current in the components mentioned above.
 The resistivity measured by using the square or aligned configuration sometimes has significant differences. Making a comparative study therefore allow to know which gap between points, which frequencies to choose when measurements must be made by using square or aligned configuration.
 In this paper, the measured thin films are made of copper which is broadly used in the structures because of its physical, chemical and mechanical properties [1]. The copper is deposited on alumina substrates by magnetron radiofrequency sputtering. Rectangular alumina substrates of dimensions 50mm x 20mm x 635μm were used. Thin film resistivity measurements using a four-point measurement method were performed by using HP 4284A LCRmeter in the frequency range of a few Hz to a few kHz. The comparison was made between the four-point aligned method and the four-point square method based on the frequency, the gap between points and the thin film thickness was made.
 The results obtained by the study show that both configurations measure the same resistivity up to 1 kHz and then the increase of resistivity in aligned configuration limits its use beyond this frequency. The square configuration can still measure the same resistivity up to 40 kHz. The study also shows that the gap between points is limited to 3 μm in aligned configuration while the square configuration allows a gap up to 5 μm.