This paper presents a novel procedure for predicting integrated circuit parametric performance and yield when provided with sample transistor test results and a circuit schematic. Two enhancements to the existing Monte Carlo simulation procedures are described: 1) a multivariate nested model is used to reproduce random process-induced device variations, rather than the multivariate multinormal model typically used, and 2) the stochastic Monte Carlo method for mapping process variability into a performance distribution is replaced with a deterministic mapping technique. The use of multivariate nested distributions allows estimation not only of correlation between various model parameters, but also allows each of those variations to be apportioned among the various stages of the process (i.e., wafer to wafer, lot to lot, etc.). This allows matched devices to be more accurately simulated, without having to develop customized models for each configuration of matching, and provides focus for process improvement efforts into those areas with the maximum potential reward. The use of deterministic mapping provides simulation results which are repeatable and do not rely on chance to insure that the process parameter space has been evenly explored. A software package which implements the entire procedure has been written in C++.

This paper demonstrates the advantages of modeling semiconductor process variability using a multivariate nested distribution. This distribution allows estimation not only of correlation among various model parameters, but also allows each of those variations to be apportioned among the various stages of the process (i.e., wafer-to-wafer, lot-to-lot, etc.). This permits matched devices to be more accurately simulated, without having to develop customized models for each configuration of matching. The technique also provides focus for process improvement efforts into those areas with the maximum potential reward. Test structures have been designed and fabricated to facilitate extraction of the parameters for the multivariate nested distribution. Using data from a sample of these structures, a process model is built and analyzed. Monte Carlo techniques are then employed using SPICE and a probabilistic process model to predict the performance of a multiplying digital-to-analog converter (MDAC), and the results are compared to measured data from fabricated circuits. Simulations performed using a model built using the multivariate nested approach are shown to provide superior results when compared to simulations using currently accepted multivariate normal models.