Patent ID: 6247998
Filing Date: 2001-06-19
Classification: B24B

Abstract:
An apparatus for use in chemical mechanical polishing a substrate having a first surface and a second surface underlying the first surface, comprising:a first optical system including a first light source to generate a first light beam to impinge on the substrate, the first light beam having a first effective wavelength, and a first sensor to measure light from the first light beam that is reflected from the first and second surfaces to generate a first interference signal;a second optical system including a second light source to generate a second light beam that impinges the substrate, the second light beam having a second effective wavelength which differs from the first effective wavelength, and a second sensor to measure light from the second light beam that is reflected from the first and second surfaces to generate a second interference signal; anda processor configured to determine a thickness from the first and second interference signals.