Patent ID: 8030631

Claim:
An apparatus for projecting multiple beams to a structure on a workpiece, the apparatus comprising: a first light source configured to generate a first illumination beam having a first plurality of wavelengths; a second light source generating a second illumination beam having a second plurality of wavelengths; an illumination primary mirror configured to reflect the first illumination beam onto a structure of a workpiece at a first angle of incidence, generating a first detection beam, and configured to reflect the second illumination beam onto the workpiece at a second angle of incidence, generating a second detection beam; an illumination secondary mirror positioned relative to the illumination primary mirror so as to make the first angle of incidence substantially the same as a calculated optimum first angle of incidence and make the second angle of incidence substantially the same as a calculated optimum second angle of incidence; a detection primary mirror configured to reflect the first and second detection beams from the workpiece; a detection secondary mirror positioned relative to the detection primary mirror so as to reflect the first detection beam off the structure through a first detection aperture and the second detection beam off the structure through a second detection aperture; wherein the optimum first angle of incidence is derived based on the first light source and a calculated numerical aperture of the first illumination beam and the optimum second angle of incidence is derived based on the second light source and a calculated numerical aperture of the second illumination beam; and wherein the illumination secondary mirror is a single piece mirror and the detection secondary mirror is a single piece mirror, the illumination secondary mirror located proximate to the detection secondary mirror.