A Measuring Method & System Studying On Resistivity Of Semiconductor Material With Digital Technology

As one of the important parameters of semiconductor materials, electrical resistivity is a main reference for judging material doping concentration. Resistivity measurement of semiconductor materials plays a very important rule in the IC manufacturing industry. Four-probe method is a common method for testing resistivity of semiconductor materials and devices. This method is simple in both principle and data processing. Therefore, it is used widely by research and production units. The traditional four-probe tester has poor performance in reliability and stability owing to the existence of discrete components, moreover, it needs to adjust switch manually and inefficiently, so it has been behind the times. With the sharp development of embedded technology, integrated and digitized measuring systems have become a development direction for various types of instruments. For the traditional four-probe tester, therefore, it needs to be researched and improved by digitized, which has very important meaning and practical value for development.This paper starts from the concept of the semiconductor resistivity and the main test methods, focused on four-probe resistivity testing principle researching, a detailed theory is derived for compensating loss for different geometry and boundary conditions of the semiconductor material. Through analyzing and comparing different circuits, combining with the embedded system design concept, finally, a digital four-probe testing system was designed by using AVR microcontroller.For the hardware part, this paper discusses each basic functional module of the composition of four-probe test system in detail, especially the two key components of the system constant current source and potentiometer. The V-I conversion circuit based on DAC is designed in the constant current source module to achieve digital. In response to the different material resistivity measurements, high-voltage constant-current structure by using the OP amplifier with extended current transistor is simulated and implemented. In the potentiometer module, inbuilt PGA and the AD7705 digital filter chip are applied which greatly simplifying the circuit structure. In order to avoid the high common-mode voltage during potential difference measurements, a magnetic coupling is used to fulfill the electrical isolation for ADC part. For man-machine interface module, a 4×4 matrix keyboard is used as input, the data is collected by the integration and processing of micro-controller, thence the test system displays the testing result on LCD obviously. At the same time, reserved interface for host computer communication which will make extensions easily. For the software part, the system software architecture is given and coding of driver for each functional module is described in detail combining with the hardware. Software filter algorithm for the processing of AD data collection have been a focal point in the paper.Sub-modules debugging and integrated testing have been done for the designed four-probe tester system. Error analysis for the measured data and improvement suggestions are given in the paper. Moreover, a summary about usage, notes and main performance of the four-probe tester system was realized through careful analysis of the system. The test results show that: the test system has greatly enhanced both in data processing capabilities and testing accuracy, in addition, its operation also very simple and efficient. As a result, the four-probe tester system designed in this paper has a high practical value and promotion prospects.