Patent ID: 7565219

Claim:
A lithographic apparatus comprising: a projection system configured to project a patterned beam of radiation onto a target portion of a substrate, a sensor; a processing unit arranged to communicate with the sensor; and a beam generator arranged to project an alignment beam to at least one of a plurality of alignment marks, of which desired positions are known, wherein the sensor is arranged to measure positional parameters for each of the plurality of alignment marks based on the projected alignment beam and to transfer the measured positional parameters to the processing unit, the positional parameters based on a plurality of diffraction orders generated by projecting the alignment beam to the at least one of a plurality of alignment marks, and wherein the processing unit is arranged to determine at least one parameter of a model providing information about a position of the substrate, based on the measured positional parameters, and wherein the measured positional parameters are weighted with variable weighing coefficients, the variable weighing coefficients based on the diffraction orders, and wherein the processing unit is arranged to determine a numerical value of at least one of the weighing coefficients and the at least one parameter of the model simultaneously.