Patent ID: 9561577
Date: 2017-02-07
CPC Classifications: B24B,H01L

Claim:
1. A method of polishing a substrate having a silicon layer, said method comprising: polishing the substrate by pressing the substrate against a polishing tool on a rotating polishing table; irradiating the substrate with only a near infrared ray having a plurality of wavelengths in a range of 800 nm to 1000 nm when polishing the substrate; receiving the near infrared ray reflected from the substrate; measuring intensity of the reflected near infrared ray at respective wavelengths; calculating relative reflectance by dividing the measured intensity of the reflected near infrared ray by predetermined reference intensity; producing a spectral waveform representing a relationship between the relative reflectance and wavelength of the reflected near infrared ray; performing a Fourier transform process on the spectral waveform to extract frequency components and corresponding strengths of the frequency components from the spectral waveform; converting the frequency components into thicknesses of the silicon layer using a predetermined relational expression; producing a frequency spectrum that represents relationship between the thickness of the silicon layer and the strength of the frequency component corresponding to the thickness of the silicon layer; determining a thickness of the silicon layer and a corresponding strength of frequency component from a peak of the frequency spectrum; identifying the determined thickness of the silicon layer as a reliable measured value if the determined strength of the frequency component is higher than a predetermined threshold value; and determining a polishing end point of the substrate based on a point of time when the reliable measured value has reached a predetermined target value.