Fig. 1. Schematic of defocus error

Fig. 2. Schematic of focus control system architecture of immersion lithography machine

Fig. 3. Focus error distribution and decomposition diagrams. (a) Total error; (b) focal length offset error; (c) y direction tilt error Ry; (d) x direction tilt error Rx; (e) y direction field curvature error Cy; (f) x direction field curvature error Cx; (g) groove type error; (h) undulating type error; (i) linear yaw error; (j) distortion error

Fig. 4. Simulation flow chart of z direction error caused by y direction tilt error Ry

Fig. 5. z-direction error distribution caused by non-normal distribution errors. (a) y direction tilt error Ry;(b) x direction tilt error Rx; (c) y direction field curvature error Cy; (d) x direction field curvature error Cx; (e) distortion error; (f) linear yaw error

Fig. 6. Distribution of the total error of z-direction (focus) errors caused by all sources of error on one exposure field

Fig. 7. Defocus error in 100000 exposure fields

Fig. 8. Probability density of defocus error in 100000 exposure fields