Sheet resistance is one of the important properties of a sheet material, the precise measurement of which is an important means to assess and monitor the semiconductor material. Meanwhile, sheet materials are widely used in the fabrication of electronic components, and the sheet resistance performance thereof directly affects the quality of the component. Sheets of metal materials, alloy materials, and semiconductor materials, and electrically conductive coating materials on a substrate are applied to the semiconductor component fabrication and electronic circuit connection, as well as the surface modification and protection of objects.
A connecting point is a small-area contact or connection between two objects, for the purpose of transmitting current. A connecting point may refer to a contact between a measurement probe and the surface of a sheet material by pressure, or a connection means between a lead and the surface of a sheet material by tin soldering (or by conducting epoxy resin), or a connection means between different objects by a warming/melting/cooling process. In addition, crystal whisker roots grown on the surface of a material can also be regarded as a connecting point. The current Chinese National Standard “GB/T 14141-2009 TEST METHOD FOR SHEET RESISTANCE OF SILICON EPITAXIAL, DIFFUSED AND ION-IMPLANTED LAYERS USING A COLLINEAR FOUR-PROBE ARRAY” has made detailed requirements on the four-probe method for testing the sheet resistance of semiconductor materials, that the probe tip should have a hemispherical shape (with a radius of 35 μm-250 μm) or a flat circular section (with a radius of 50 μm-125 μm).
The potential field in the sample generated by the two terminal electrodes in the collinear four-probe array method is unavoidably affected by the two middle measuring electrodes. This standard strictly requires that the distance between adjacent probes be 1.59 mm, which limits the application range of the sample. Repeated testing is required to ensure the reliability of measurement results as well as to improve the measurement accuracy, as the shape of the indentation by the probe on the surface of the tested material is difficult to control. In short, the process using collinear four-probe array method for measuring the sheet resistance of a sheet material is complicated, and demanding on the measurement instruments and operation skills, which limits its application.
In addition, the Chinese National Standard “GB/T 15078-2008 TESTING METHOD FOR CONTACT RESISTANCE OF PRECIOUS METALS ELECTRICAL CONTACT MATERIALS” specifies the measurement of (static) contact resistance between a probe made of precious metals and their alloy materials and a bulk material in detail. However, this standard does not apply to a sheet material due to the relatively high resistance of the sheet material itself. The connection at the cross-section of the connecting point is usually estimated from experience or analyzed by slicing. There is currently no standard method for measuring the contact resistance of the connecting point of a sheet material.
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