We derive a physical model to describe the dependence of pattern dimensions on dose, defocus and blur. The
coefficients of our model are constants of a given lithographic process. Model inversion applied to dimensional
measurements then determines effective dose, defocus and blur for wafers patterned with the same process.
In practice, our approach entails the measurement of proximate grating targets of differing dose and focus sensitivity. In
our embodiment, the measured attribute of one target is exclusively sensitive to dose, whereas the measured attributes of
a second target are distinctly sensitive to defocus and blur. On step-and-scan exposure tools, z-blur is varied in a
controlled manner by adjusting the across slit tilt of the image plane. The effects of z-blur and x,y-blur are shown to be
equivalent. Furthermore, the exposure slit width is shown to determine the tilt response of the grating attributes. Thus,
the response of the measured attributes can be characterized by a conventional focus-exposure matrix (FEM), over which
the exposure tool settings are intentionally changed. The model coefficients are determined by a fit to the measured
FEM response. The model then fully defines the response for wafers processed under "fixed" dose, focus and blur
conditions. Model inversion applied to measurements from the same targets on all such wafers enables the simultaneous
determination of effective dose and focus/tilt (DaFT) at each measurement site.