Measurement of Surface Roughness and Thickness of Silicon Wafers Using an Infrared Laser

Abstract

A non-contact method of measuring the surface roughness and the thickness of polished silicon wafers using an infrared laser is proposed. The method utilizes the property that the infrared radiation is transmitted through single-crystal silicon. An optical-power meter is used to measure the intensity of an infrared laser beam that is incident to a chamfer on a cornered silicon wafer and which exits from the other side of the chamfer after repeated total reflections inside the wafer. The experimental results show that a significant correlation exists between the intensity of the transmitted infrared radiation and the surface roughness of the silicon wafers, as well as between the intensity and the thickness of the wafers. Therefore, if a calibration curve is pre-set, the surface roughness and the thickness can be estimated from the changes in the intensity of the infrared transmittance.