Analysis And Fitting Calculation Of The Source/Drain Series Resistance In MOSFETs

With the development of micro-electronics industry, to adapt the development of integrated circuit technology and improve the integration degree of the system, the size of the semi-conductor device continues to shrink. The reduction of MOSFET size, can reduce power consumption and improve integration, however, at the same time it will inevitably lead to changes in the characteristics and performance of the MOSFET. Therefore, to improve the performance of MOSFET, the in-depth study of the electrical characteristics of small size MOSFET is of great significance. The study of source/drain resistance in series with the conductive channel in MOSFET is very important for the accurate simulation of the small size device and integrated circuits performance, and has great significance for the performance optimization and process improvement of the device. Therefore, the research on the source/drain series resistance is always the hotspot in the micro-electronics industry. At present, many research methods of MOSFET source/drain resistance have been developed. These methods both have their own advantages and disadvantages; the main disadvantage of which are that the calculation procedure is cumbersome and the formula is complex. In view of the defects of the existing research methods, this thesis presents an analytical and computational method based on numerical simulation. The advantages of this method are that, the theory of analysis is simple and only a few physical parameters need to be considered which makes the relationship between the physical parameters and source/drain resistance clear and intuitive. Furthermore, the analytical expression of the calculated resistance can be obtained directly and has a high accuracy. The work done in this thesis can be summarized as follows.Firstly, we study the existing methods of MOSFET source/drain series resistance, and make a full theoretical analysis and summary. At present, the most commonly used research methods can be separated into two methods, extraction method and modeling method. In this thesis, these two methods are described in detail. Moreover, the two methods are summarized and the advantages and disadvantages of the variety of specific research methods of them are described in detail.Secondly, based on the understanding and analysis of these existing methods, we propose a method of source/drain intrinsic resistance analysis and calculation method. The method is based on numerical simulation and can obtain the explicit analytical expression, the result of which is of high accuracy. The specific implementation of the method is as follows. First step, a variety of MOSFET with different physical parameters is simulated and the classic channel resistance method (CRM) is used to extract the source/drain intrinsic resistance. Second step, the physical parameters and the simulation data are analyzed and the physical parameters which influence the source/drain resistance in MOSFET are obtained. Third step, the simulation results are combined with the physical parameters to obtain the multiple linear fitting of these parameters. After the three steps, the calculation formulas of source/drain intrinsic resistance and the physical parameters which influence source/drain intrinsic resistance can be solved.Finally, through the simulation verification, we can find that the fitting resistance formula is of high accuracy. According to the analysis and fitting calculation of the source/drain resistance simulation results, we obtained three main conclusions. The first conclusion, there are three physical parameters which influence the source/drain resistance, respectively:the junction depth of the source/drain regions in device, source/drain doping resistivity of the source/drain regions, and the distance between conductive channel and the source/drain electrode. The second conclusion, there is current crowding effect on source/drain electrode. In MOSFET source/drain regions, the carrier flow to source/drain electrode from conductive channel mainly crowd in a very small area on the source/drain electrode which is near the gate, which generates current crowding effect in that region. The third conclusion, the expression of the source/drain intrinsic resistance can be solved. The maximum error between simulation and calculation is only 4.4%. Moreover, the change of channel length has little influence on the source/drain intrinsic resistance.In this thesis, the MOSFET source/drain intrinsic resistance calculation formula and the conclusions, have reference significance and practical value for us to calculate the MOSFET source/drain resistance and analysis its physical parameters and electrical characteristics.