Waveguide based parallel multi-phaseshift interferometry for high speed metrology, optical inspection, and non-contact sensing
AssigneeKLA-Tencor Corporation
InventorsDavid Peale, Carlos Duran, Harald Hess
Life of this patent
Estimating the term…
Abstract
An interferometer that contains a tri-coupler to mix light from three different waveguides. The light is emitted from a light source and may be reflected from a test surface. The output of the tri-coupler may be three different light beams that have intensities 120 degrees out of phase from each other. The out-of-phase light beams may be detected by a plurality of photodetectors. The detected out-of-phase light beams may be used to determine a height of the test surface. The waveguides and tri-coupler provide a compact and relatively inexpensive interferometer.
Claims7
An apparatus that can measure optical phase variations in or along an object volume or surface with respect to a reference surface comprising:
- a light source that emits light;
- a first waveguide that guides light reflected from the object surface;
- a second waveguide that guides light;
- a third waveguide that guides light reflected from the reference surface;
- a tri-coupler that mixes the reflected light within said first and third waveguides and provides a first output light beam within said first waveguide, a second output light beam within said second waveguide, and a third output light beam within said third waveguide;
- a first photodetector that detects the first output light beam and generates a first output signal;
- a second photodetector that detects the second output light beam and generates a second output signal;
- a third photodetector that detects the third output light beam and generates a third output signal;
- and
- a controller that receives said first, second, and third output signals and computes a phase difference between the first and third input beams from said first, second and third output signals.
A method for interfering and detecting light, comprising:
- reflecting a first light beam from an object surface;
- reflecting a second light beam from a reference surface;
- coupling the first light beam from a first waveguide to a second waveguide and a third waveguide, and the second light beam from the third waveguide to the first and second waveguides to create a first output light beam in the first waveguide, a second output light beam in the second waveguide, and a third output light beam in the third waveguide;
- detecting the first, second, and third output light beams;
- and,
- computing a phase angle from the detected first, second, and third output light beams.
Dependencies are inferred from the claim text.