Method for monitoring focal length variation of online products by utilizing SCD

[0019] combine figure 1 As shown, in order to demonstrate the ability of SRM, an advanced lithography step level is designed below, that is, an experiment using separate light source energy and focus to make photoresist topography with different contours, and prepare four FEM wafers (at least Four, not less than four) and five (at least five, not less than five) POR (process of Reference, process reference test piece) wafers, and measure the critical dimension by scatterometry.

[0020] The SRM parameters have been trained by the CDSEM of 4 FEM wafers, and achieved an excellent R2 (statistical coefficient of determination), which is used in statistics to measure the proportion of the variation of the dependent variable that can be explained by the independent variable. This is used to judge the accuracy of the statistical model (closer to 1 is better) and linear slope (0.98 and 1.1 respectively). see figure 2 Shown, wherein, R2=0.9814, linear slope Y=1.1072X-5.9777. figur...