Experimental results on optical proximity correction with variable threshold resist model

In previous work we combined fast aerial image simulation with a closed-loop Optical Proximity Correction (OPC) control system to generate pre-compensated mask geometries which account for pattern transfer distortion effects at small feature sizes. We also presented the variable-threshold resist (VTR) model in which an image-dependent threshold is used to calculate linewidths directly from the image intensity. The model parameters can be determined by ''tuning'' the model with linewidth measurements from chosen sample sites on the wafer. In this paper, we present verify our OPC approach experimentally by showing after etch SEM wafers of corrected and uncorrected designs. In doing so, we show that (a) OPC can eliminate bridging effects in uncorrected designs, (b) VTR model is fairly insensitive to process variations and (c) mask writing effects are important and cannot be ignored.