Patent ID: 7499178
Filing Date: 2009-03-03
Classification: G01B

Abstract:
1. An oblique incidence interferometer for applying a light at a certain angle from the normal to a measurement surface of a target to be measured and measuring a light reflected from said target, comprising: a light source; a beam splitter/synthesizer unit which splits the light from said light source into a measurement light to be applied to said target and a reference light serving as the measurement reference, and which orthogonalizes the polarization directions of said measurement light reflected from said target and said reference light and synthesizes said lights to yield a synthesized light; a beam splitter unit which splits said synthesized light into a plurality of split lights; a plurality of imaging units which captures a plurality of interference fringe images formed in accordance with said plurality of split lights; a ¼-waveplate provided on either one of an entry side and an exit side of said beam splitter unit; a plurality of polarizers provided on imaging surfaces of said plurality of imaging units and arranged having respective different polarization axes; and an operation unit which computes a surface form of said target based on said interference fringe images captured by said imaging units and resulted from said plurality of split lights having phases shifted through said polarizers, wherein said beam splitter/synthesizer unit includes means for splitting the light from said light source into two light beams having orthogonal polarization planes and generating two collimated beams having different optical axes and a certain diameter; a triangular prism which transmits one of said two beams therethrough and reflects the other therefrom, thereby splits said two beams into a measurement light and a reference light serving as the measurement reference, and which synthesizes said measurement light with said reference light to yield a synthesized light, and a spatial filter unit which passes said synthesized light therethrough and rejects a noise light caused from one of said two beams reflected from said triangular prism and a noise light caused from the other of said two beams transmitted through said triangular prism.