1. A method, comprising: providing a model for a device parameter of a wafer as a function of first and second process parameters, the first and second process parameters corresponding to different wafer characteristics, respectively; deriving target values of the first and second process parameters based on a specified target value of the device parameter; performing a first fabrication process in response to the target value of the first process parameter; thereafter measuring an actual value of the first process parameter; updating the model using the actual value of the first process parameter; deriving a revised target value of the second process parameter using the updated model; and performing a second fabrication process in response to the revised target value of the second process parameter.