Patent ID: 7388651
Filing Date: 2008-06-17
Classification: G03F

Abstract:
1. A method of monitoring a magnitude and a direction of deviation of a first actual focus position of a focus-monitoring mark included in a reticule pattern, from an optimum focus position, said reticule pattern having been transferred onto a wafer at said optimum focus position by photolithography, said method comprising the steps of: (1) creating a calibration quadratic function curve representing a relationship between a dimension and a focus position of said focus-monitoring mark transferred onto said wafer; (2) transferring at least one shot of said focus-monitoring mark onto said wafer at a first focus position, which is defocused by a certain amount from a second focus position where said calibration quadratic function curve takes an extreme value thereof; (3) measuring a dimension of said focus-monitoring mark, which has been transferred onto said wafer in said step (2); (4) calculating a second actual focus position of said focus-monitoring mark, which has been transferred onto said wafer in said step (2), by using said calibration quadratic function curve and said dimension measured in said step (3), wherein when said first focus position is smaller than said second focus position, a smaller solution of two solutions found from said calibration quadratic function curve is determined as said second actual focus position, and when said first focus position is larger than said second focus position, a larger solution of said two solutions is determined as said second actual focus position; and (5) subtracting said first focus position from said second actual focus position to find said magnitude and said direction of said deviation of said first actual focus position from said optimum focus position.