Design And Fabrication Of A Simple Four Point Probe System For Electrical Characterization Of Thin Films

ABSTRACT

The electrical characteristics of semiconductor thin films are of great practical interest in microelectronics industry hence the need to measure these parameters in a cheaper and faster manner possible. This study has embarked on design and fabrication of a simple, effective and portable computer-aided four point probe system for thin film sheet resistivity measurement. A four point probe head has been designed and fabricated from easily available materials. A relay switching device has also been designed and fabricated to perform switching of the probe tips on the sample surface as per the Van der Pauw set up. A Keithley SourceMeter 2400 model has been interfaced to a LabVIEW running computer via the serial port (RS-232 port) for its full control by the computer. The relay switching device has also been interfaced to the computer via the printer port (LPT1 port). The fabricated probe head, the relay switching device and Keithley SourceMeter were used to probe the samples as per the Van der Pauw set up with a square symmetry adopted for sheet resistivity measurement. To test the workability and reliability of the fabricated system for thin film sheet resistivity measurement, the sheet resistivity of Cu2O semiconductor thin films prepared by DC reactive magnetron sputtering technique were measured. The sheet resistivity measured at room temperature of 23 oC was found to be 55.65 Ω cm. However, as the samples were exposed to temperature rise, the sheet resistivity was found to decrease and was at its minimum value of 29.67 Ω cm at 170 oC. Cu2O thin films prepared at different sputtering pressures were also electrically characterized using the system. The sheet resistivity of the thin films were found to increase with increase in sputtering pressure. Films deposited at sputtering pressure of 1.8x10-2 mbar had sheet resistivity of 33.63 Ω cm and this increased to 62.23 Ω cm for films prepared at higher sputtering pressure of 2.4x10-2 mbar. From the measurements obtained, it was found from the study that the system offers a reliable, effective and simple technique for thin film sheet resistivity measurements.