Method of measuring thickness of a semiconductor layer and method of manufacturing a semiconductor substrate

A method of measuring the film thickness of a semiconductor substrate that includes a first layer and a second layer, wherein the refractive index of the second layer is different from that of the first layer, and wherein the film thickness of the first layer is measured based on light reflected from the substrate, the method comprising:

• radiating light onto the substrate;
• breaking light reflected from the substrate into a spectrum by wavelength;
• collecting complete optical interference data by wavelength of the reflected light;
• and
• calculating the film thickness d of the first layer using the following equation:
• d = λ 1 · λ 2 λ 2 · n ⁢ ( λ 1 ) - λ 1 · n ⁢ ( λ 2 ) · ( X + s 1 - s 2 ) 2
• where λ1 and λ2 are wavelengths corresponding to arbitrary peaks, wherein the peaks include maximum and minimum values, n(λ1) is the refractive index of the film at wavelength λ1, n(λ2) is the refractive index of the film at wavelength λ2, X is the wave number between the two wavelengths, and s1 and s2 are phase shift amounts at wavelengths corresponding to the peak values, respectively, between a single layer film structure and a double layer film structure.