Now the resist height upon developing must be calibrated to UV exposure energy, from which the optical density of the device features in the mask may be determined. To this end, the resist height that results from an optimized lithography process was calibrated with a range of optical densities from a reference mask. From this information, the device height profile is encoded into the optical density profile necessary to produce it. The calibration is valid only for the particular lithography process parameters employed and would need to be changed if the lithography process were altered, . in.
