Development of a Thickness Meter for Conductive Thin Films Using Four-Point Probe Method

Abstract

A thin film thickness meter was developed that is essential for thin film thickness management in the manufacturing process of flat panel displays such as touch panels and touch screens. The thickness measurement method of the meter is based on four-point probe method (Arther Uhlir in The Potentials of Infinite Systems of Sources and Numerical Solutions of Problems in Semiconductor Engineering 34:105-128, 1955; Valdes in Resistivity Measurements on Germaniumfor Transistors 42:420-427, 1954) and in the method, a thickness is determined by dividing the known electrical resistivity of a thin film material by the sheet resistance, and the thin film thickness measurement range is practically 1 nm–1 mm although the performance of the meter was confirmed in the range of 2.2 nm–22 μm. In order to conveniently measure the thickness of a thin film sample at a desired (to be measured) position, a probe station and a four-point probe were made. Place the four-point probe and the thin film sample at the probe station. When the four-point probe is brought into contact with the surface of the thin film sample using the upper and lower control knobs, the thickness measurement value is displayed on the meter, so the thickness of the thin film can be measured quickly and accurately. In addition, 5 types of samples such as Pd, Al, Au, Nb, and Cu were used to confirm the performance of the measuring device for the thin film thickness measurement function. For sample preparation, 5 types of samples were deposited on a silicon wafer with 75 mm in diameter, and the thickness was measured within 10 mm of the center of the sample, and the thickness of the cross-section was observed by SEM and TEM. As the result, the agreement for the thickness values between by the measurement results and SEM or TEM was confirmed in the range of 14 nm–1.6 μm.