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Pulsed Magnetic Field Contactless Testing of Wafer-Shaped Sample Electrical Properties

IP.com Disclosure Number: IPCOM000039644D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Braslau, N: AUTHOR

Abstract

The sensitivity of contactless test apparatus using reflected microwave signals from semiconductor wafers that fill an entire waveguide, where the reflected signal at zero magnetic field is related to sheet resistance and the reflected signal in the presence of a magnetic field is related to mobility, can be increased by employing a pulsed magnetic field. The apparatus is shown in Fig. 1. Three voltages would have to be acquired and stored: (1) the detected forward, (2) the reflected power of the reflectometer, and (3) the output of a calibrated field sensor, for example, a Hall effect sensor as offered commercially by Microswitch division of Honeywell. The response time of video diodes and such Hall sensors is adequate for following pulses of this time scale. (Image Omitted) Two alternatives are available for the apparatus.

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Pulsed Magnetic Field Contactless Testing of Wafer-Shaped Sample Electrical Properties

The sensitivity of contactless test apparatus using reflected microwave signals from semiconductor wafers that fill an entire waveguide, where the reflected signal at zero magnetic field is related to sheet resistance and the reflected signal in the presence of a magnetic field is related to mobility, can be increased by employing a pulsed magnetic field. The apparatus is shown in Fig. 1. Three voltages would have to be acquired and stored: (1) the detected forward, (2) the reflected power of the reflectometer, and (3) the output of a calibrated field sensor, for example, a Hall effect sensor as offered commercially by Microswitch division of Honeywell. The response time of video diodes and such Hall sensors is adequate for following pulses of this time scale.

(Image Omitted)

Two alternatives are available for the apparatus. (a) use a sample-and-hold circuit or a boxcar circuit which would sense the voltages at the peak of the pulse with repetitive pulses at increasing values of the capacitor charging voltage, (b) using a fast A/D converter, sample the three voltages at intervals during one pulse, on the leading edge, peak, and trailing edge, using the associated computer to calculate the ratio of reflected to forward voltage for the field at each interval, as illustrated in Fig. 2. Use of this technique depends on the details of these A/D converters and on the use of amplifiers with adequate slew rates, as the ava...