Film thickness analysis method

The invention provides a film thickness analysis method which comprises the following steps: calculating the measured reflectivity of a to-be-measured sample according to the measured light intensity of the to-be-measured sample; matching the measured reflectivity with the theoretical reflectivity in a simulation spectrum library; obtaining the theoretical reflectivity corresponding to the minimum variance, and taking the corresponding thickness value of each layer of film as the film thickness initial value of the sample to be detected; performing iterative optimization on the film thickness initial value of the to-be-measured sample based on an LM nonlinear regression algorithm, and solving an optimal film thickness value of the to-be-measured sample; calculating the correlation between the measured reflectivity and the theoretical reflectivity; if the correlation is smaller than a set threshold value, the measured reflectivity is subjected to de-trending processing, matching is conducted again in the simul