Spatial Analysis of Ring Oscillator Devices

— Spatial dependencies tend to introduce correlations among parameter values obtained from test structures. These spatial correlations obscure the parameter correlations caused by common underlying variables and make process diagnosis more difficult. In this work, linear regression method has been used to generate the spatial models for both wafer and chip level to investigate their significance. It is found that the wafer level regression model does not have a strong wafer level dependence on the ring oscillator devices. On the other hand, at the chip level, goodness of fit calculated for certain device structures exhibit strong spatial dependence on the linear regression model. This proves that it is essential to consider different levels of spatial dependence before making conclusion on the variations caused by underlying variables and parameter.