MICROWAVE DEVICE FOR NONDESTRUCTIVE MAGNETORESISTANCE MEASUREMENT OF SEMICONDUCTING LAYERS

We propose a novel non-destructive method which allows us to determine the sheet resistance R square, the mobility mu and the density n of t he free carriers of semiconducting layers. Superficial or buried layer s can be measured. The sample may be of any shape and, in particular, this method is useful to characterize wafers. The measurement cell con sists of two microstrip lines on a flexible duroid substrate. The ends of these lines are covered with a thin insulator layer and act as ele ctrodes. To characterize a sample, the electrodes are simply pressed o n it and a measurement of the modulus of the transmission factor betwe en the two lines is performed. Eliminating the scattering factor phase leads to a simplification of the experimental set-up and a lowering o f its cost. At the working frequency (1-2 GHz), the impedance values o f the capacitive contacts are small with respect to R square. Therefor e, the resistance between the two electrodes and R square are easily o btained. The determination of mu is achieved from magnetoresistance me asurements. Then, the value of n can be calculated if the thickness of the layer is known. The measurement ranges are as follows: 100 OMEGA < R square < 3 kOMEGA; 2000 cm2 V-1 s-1 < mu. The accuracy of the resu lts achieved with our method or the van der Pauw method is similar. La stly, the measurement system is controlled by a microcomputer; thus, t he R square, mu and n mapping of a 2 in wafer takes about 1 min per si te (a site corresponds to a tested area with dimensions of about 5 mm x 5 mm).