A thickness estimation method may include: obtaining a test spectrum image; obtaining test spectrum data; measuring a thickness of a test layer formed on the test substrate at the plurality of positions; generating a regression analysis model using a correlation between the thickness of the test layer and the test spectrum data; obtaining a spectrum image; and estimating a thickness of a target layer over the entire area of the semiconductor substrate by applying the spectrum image to the regression analysis model. The thickness corresponding to the entire area of the semiconductor substrate that is being transferred is estimated using the thickness estimation method according to an exemplary embodiment in the present disclosure, such that whether or not processing is normally performed may be examined without requiring a separate time. In addition, an examination result may be feedbacked to processing equipment to improve production yield.