Project number
25034
Organization
ASML US, Inc.
Offering
ENGR498-F2024-S2025
Photolithography machines use optical alignment sensors to precisely position and overlay photomask layers by detecting the reflection of polarized light from silicon wafer gratings. High alignment accuracy is crucial for wafer pattern transfer quality. This can be optimized using unpolarized light, which has the potential to maximize total signal detection. It is achieved by using coherent light sources and a depolarizer.
The team developed two theoretical models for depolarizing a broadband, visible/near-infrared input beam of any polarization state: Fiber Ring and Lyot. They chose the Lyot depolarizer and conducted experimental verification on a prototype of this passive, all-fiber model.
The Lyot depolarizer is made of two lengths of polarization-maintaining fiber spliced together, with one rotated 45 degrees relative to the other. The team selected a red fiber-coupled superluminescent diode as the coherent source for experimental setup. The light from this diode is routed through free space to control its polarization state, coupled into the depolarizer, and emitted back into free space, where the team took measurements with a Stokes polarimeter to verify the degree of polarization.
The team developed two theoretical models for depolarizing a broadband, visible/near-infrared input beam of any polarization state: Fiber Ring and Lyot. They chose the Lyot depolarizer and conducted experimental verification on a prototype of this passive, all-fiber model.
The Lyot depolarizer is made of two lengths of polarization-maintaining fiber spliced together, with one rotated 45 degrees relative to the other. The team selected a red fiber-coupled superluminescent diode as the coherent source for experimental setup. The light from this diode is routed through free space to control its polarization state, coupled into the depolarizer, and emitted back into free space, where the team took measurements with a Stokes polarimeter to verify the degree of polarization.