To calculate depth of hole or step with high precision by eliminating the effect of thickness of resist film during execution of etching.
The light of predetermined wavelength width is radiated to a sample 50, and the light containing interference with the light reflected on a bottom surface of a hole 52 or an upper surface of a substrate 51, and the like is subjected to spectral detection by a spectroscope unit 25. At a data processing part 30, an interference spectrum is obtained that is provided by removing effects or the like of an emission spectrum of a light source 21 from spectral profile, which is then subjected to Fourier transformation to provide a peak interval, for calculating depth of a hole, film thickness, or the like. Since a chopper 103 periodically allows shielding/passing of external reference light that is reflected on an external reference surface 104, a data processing part 30 provides data with external reference light and data with no external reference light. For example, during the period when a resist layer 53 is thick, a depth of hole or the like is calculated based on the data with no external reference light which has higher resolution, but when the resist layer 53 becomes thinner as etching proceeds, a depth of a hole or the like is calculated based on the data with external reference light which is hard to be affected by disturbance.
ARAKAWA AKIRA
NAGUMO YUZO
TSUNASAWA YOSHIO
