Computer-aided simulation of transistor fabrication, characterization, and optimization

A systematic and general method of computing ac and dc characteristics of double-diffused junction transistors is described using major process parameters such as: dimensions of the device, surface concentration, junction depth, diffusion time, temperature, and diffusion coefficient as a function of temperature and impurity concentration. These parameters can be checked during the process and, therefore, can aid the process control problem by predicting the expected values of junction depth and sheet resistivity. If the specified control parameters are met during the fabrication, the ac and dc characteristics of the device will be realized. The time and/or frequency response of a circuit can be computed using the ac and dc characteristics of the diffused devices of the circuit on the basis of a distributed or an equivalent lumped model. The measurement of important ac parameters on the basis of these models has also been simulated on the computer, thus aiding the characterization problem of the device in the integrated circuit environment. Also, the switching speed of a loaded logic net can be computed and optimized by trading off interacting parameters and relating them back to the original diffusion process parameters and dimensions of the components. Finally, experimental verification of the computed results has been accomplished and found to be satisfactory.