Research Of ESD Simulation Technology

As the development of semiconductor process technology, ESD (Electrostatic Discharge) has been an increasingly grave threat to ICs. Therefore, the research on ESD protection design has attracted more and more attention. The applications of simulation tools on ESD area make the design of ESD protection devices more convenient, and greatly shorten the development cycle.However, due to the complicated physical mechanism of ESD, the extremely high field and high temperature when ESD happened, and the frequently convergence problem in ESD simulation, it becomes difficult to carry out the ESD simulation. To solve this problem, this paper concentrates on the simulation of ESD protection devices, based on the ISE TCAD platform. And the main content of this paper include:First, this paper points out the importance of mesh definition in process simulation, and detailed the method of mesh definition. Besides, the physical models used in process simulation are analyzed in detail, and the differences among the models which describe the same process step are also discussed, as well as the key parameters in physical models which greatly impact the simulation results.Second, physical models and functions used in device simulation are analyzed, including the transport equations, band modes, mobility degradation models, impact ionization models, recombination models.Third, the physical mechanisms related are investigated when ESD happens, and the relevant physical models which should be chosen in device simulation are listed. This paper also discusses the impact on simulation results caused by the changes of key parameters of physical models, such as the ionization factor, the mobility and the lifetime of carries.Forth, convergence problems caused by different reasons are discussed, and the solutions are presented.Fifth, through the modification of key parameters of physical models, this paper simulates 22 devices which are based on three kinds of SCR (Silicon Controlled Rectifier), and compares them with the TLP tested data. The results show that all the relative errors of trigger voltages and holding voltages simulated are less than 10%.Sixth, a novel simulation method is proposed which can not only simulate trigger voltage and holding voltage correctly, but also greatly improve the precision when evaluating the second breakdown current. Two methods are also provided to determine when the second breakdown happens, and they are proved by the comparison of simulation results and TLP test results.