Method and apparatus for nondestructive measurement and mapping of sheet materials

The invention described in this patent application relates to nondestructive measurement and mapping of materials, particularly using microwaves in the measurement of carrier concentration and mobility and sheet resistance in semiconductor wafers and flat panel displays. An apparatus for contactless measurement of carrier concentration and mobility includes a microwave source, a circular waveguide for transmitting microwave radiation to a sample, such as a semiconductor wafer or panel for flat panel displays, at a measurement location, a first detector for detecting the forward microwave power, a second detector for detecting the microwave power reflected from the sample, and a third detector for detecting the Hall effect power. A circular waveguide, carrying only the TE11 mode, is terminated by the sample behind which a short is located. Perpendicular to the plane of the sample (and along the axis of the circular waveguide), a magnetic field is applied. In this configuration, a given incident TE11 wave will cause two reflected waves. One is the ordinary reflected wave in the same polarization as the incident one. A detector is provided to measure this reflected radiation. The other reflected wave is caused by the Hall effect. Its polarization is perpendicular to the former wave and a probe is provided to detect this as well. This reflected wave is detected by a probe, the output of which is combined with an attenuated and phase shifted portion of the forward radiation at a single detector.