The accurate prediction of relevant optical and other processing effects is the essential first element of optical proximity effect (OPC) methodologies. A quasi-empirical modeling technique has been devised. Starting from standard aerial-image energy deposition, an exponential transfer function is employed to account for saturation effects. This is then followed by a double-Gaussian diffusion convolution. Finally, a novel 2-dimensional log-slope model was devised to better predict some DUV processes. The model parameters are derived from a few empirical measurements and a fitting process. The calibrated model is then used by a rule-based OPC package to correct a variety of structures. Efficient verification techniques suitable for large area designs are introduced.
The feasibility of manufacturing 280 nm gates for ASIC technology using i-line lithography is examined. Off-axis illumination, sub-resolution assist features and proximity effect bias corrections were considered. The experiments were performed with a reticle designed to evaluate the effects of line pitch, bias and field uniformity on the feature dimensions. Results show that dense and isolated features were found to print at about the same linewidth under all three illumination conditions. However, deviations as large as 40 nm were found at intermediate pitches, implying that some form of optical proximity correction is needed to maintain critical dimension (CD) control for a mask pattern with varying feature densities. Sub-resolution assist lines adjacent to isolated 280 nm lines significantly improved the apparent wall angle of the features compared to true isolated features. The use of these features comes at a cost; the sub-resolution features can be printed under certain conditions and could possibly lead to device failure. Multi-dimensional matrices of CD measurements with varying dose, focus, bias and pitch, when displayed in an appropriate manner, are being used to identify the relative advantages of different illumination conditions. Off-axis illumination offers a large depth of focus for all pitches if proximity effect biasing is applied. Conventional illumination with biasing can improve exposure latitude.