Patent ID: 6657737
Filing Date: 2003-12-02
Classification: G01B

Abstract:
A film thickness measuring method wherein light is applied to a film to be measured, and reflected light from upper and lower interface surfaces of the film is received to measure a thickness of the film, said film thickness measuring method comprising:measuring a spectral reflectance ratio S(&lgr;) at a spot where the film to be measured is present by using light having a plurality of different wavelengths &lgr;, wherein each wavelength &lgr; is within a measuring wavelength range &lgr;1&lE;&lgr;&lE;&lgr;2; measuring a spectral reflectance ratio R(&lgr;) at a spot where the film to be measured is not present by using the light having a plurality of different wavelengths; determining a measured spectral reflectance ratio Rmeas(&lgr;)=S(&lgr;)/R(&lgr;); determining a theoretical value Rcalc(&lgr;) of spectral reflectance ratio at an assumed film thickness d; determining an evaluation value Ed from a square-sum of differences between the measured spectral reflectance ratio Rmeas(&lgr;) and the theoretical value Rcalc(&lgr;) of spectral reflectance ratio at the film thickness d according to the following equation: Ed=&Sum;Î»=Î»&it;â€ƒ&it;1Î»&it;â€ƒ&it;2&it;â€ƒ&it;(Rmeas&af;(Î»)-Rcalc&af;(Î»))2â€ƒchanging the film thickness d by increasing or decreasing the film thickness d in steps of &Dgr;d in a measuring retrieval range of from d1 to d2 to determine an evaluation value Ed at each relevant film thickness, thereby obtaining an evaluation function E(d) with respect to the film thickness d; assuming a spectral reflectance ratio Rmeas(&lgr;e) of the film to be equal to 1 and determining an evaluation value Enewd from a square-sum of differences between a theoretical value Rcalc(&lgr;e) of spectral reflectance ratio at a certain film thickness d and the spectral reflectance ratio Rmeas(&lgr;e)=1 according to the following equation: Enewd=&Sum;Î»&it;â€ƒ&it;e=Î»&it;â€ƒ&it;1Î»&it;â€ƒ&it;2&it;â€ƒ&it;(Rcalc&af;(Î»&it;â€ƒ&it;e)-1)2â€ƒchanging the film thickness by increasing or decreasing the film thickness d in steps of &Dgr;d in a measuring retrieval range of from d1 to d2 to determine an evaluation value Enewd at each relevant film thickness, thereby obtaining an evaluation function Enew(d); determining a ratio PE(d) of the evaluation function E(d) to the evaluation function Enew(d) as follows: PE(d)=E(d)/Enew(d); and determining a film thickness d that gives a minimum value of the ratio PE(d) to be a measured film thickness value D.