Patent ID: 6757056
Filing Date: 2004-06-29
Classification: G01B,G01N,H01L

Abstract:
A system for measuring a phase difference between light signals reflected from both sides of a first object comprising:a first light source for transmitting a first incident light signal toward a first surface of said first object in a first plane of incidence; a first polarization splitter for separating, from a first reflected light signal that has reflected off said first surface, a first mixed reflected polarized light signal component having a first phase and a second mixed reflected polarized light signal component having a second phase different from said first phase, wherein said first mixed reflected polarized light signal component comprises both P-polarized and S-polarized light relative to a plane of incidence of said first incident light signal, and wherein said second mixed reflected polarized light signal component comprises both P-polarized and S-polarized light relative to the plane of incidence of said first incident light signal; a first detector for detecting a first intensity of said first mixed reflected polarized light signal component; a second detector for detecting a second intensity of said second mixed reflected polarized light signal component; a first phase determinator for determining a first difference in phase between said first and second mixed reflected polarized light signal components based upon said first and second intensities; a second light source for transmitting a second incident light signal toward a second surface of said first object in a second plane of incidence different from the first plane of incidence; a second polarization splitter for separating, from a second reflected light signal that has reflected off said second surface, a third mixed reflected polarized light signal component having a third phase and a fourth mixed reflected polarized light signal component having a fourth phase different from said third phase, wherein said third mixed reflected polarized light signal component comprises both P-polarized and S-polarized light relative to a plane of incidence of the second incident light signal, and wherein the fourth mixed reflected polarized light signal component comprises both P-polarized and S-polarized light relative to the plane of incidence of the second incident light signal; a third detector for detecting a third intensity of said third mixed reflected polarized light signal component; a fourth detector for detecting a fourth intensity of said fourth mixed reflected polarized light signal component; and a second phase determinator for determining a second difference in phase between said third and fourth mixed reflected polarized light signal components based upon said third and fourth intensities.