Design Of Sheet Resistance Tester Based On Four Point Probe Technique

The semiconductor industry is the foundation of modern information industry,the uniformity of the doping of the wafer is directly related to the semiconductor quality,especially the quality of the integrated circuit. The sheet resistance is a direct and important parameters which is on behalf of the characterization of the wafer doping uniformity, and it is also one of the important indexes in the semiconductor manufacturing process.At present,the international main measuring method of the silicon wafer sheet resistance is four point probe test technology, but the domestic four point tester is slow in testing speed, low in automation degree, and it is unable to position accurately. So, it is a large gap between the domestic equipment with the foreign sheet resistance equipment. Therefore, this paper is devoted to design an more automation and integration sheet resistance tester, which is based on the technology of four point probe.The system is designed based on the classical four point probe technology, and the system is used stepper motor driver with subdivision controller to slide precision in the horizontal movement, and used linear motor and the way dead-weight to control the probe moving in the vertical direction, so it can achieve the accurate points on the wafer when measuring. The system used STM32 MCU as the control core, and designed the friendly man-machine interface touch screen for spotting, controling the testing range with automatic matching, testing the wafer and processing the data automaticly, and output a variety data of forms in final. In the measurement unit of the system, it designed the precision constant current source, which is cooperate with the voltage measurement circuit with 20 bit modulus conversion, and to realize the stable current output by the negative feedback way. At the same time, to achieve the productization of the system, a dedicated power supply circuit and protection circuit is designed.By experimental verification, the system is able to achieve the expected goal. It is ableto finish up to 49 points sheet resistance test, and the testing speed is up to ?5.02 s/point.The range of the sheet resistance is 20?/sq ~ 20k?/sq, and the repeatability precision can reach ±2%. So, the system can realize the automation and integration in measuring. To a certain extent, it makes up for the deficiency of the domestic sheet resistance tester, and has a certain application value.