Frequency encoding scheme for reticle front and back side inspection

Michal E. Pawlowski; Corey Loke; Aage Bendiksen; Peter Kochersperger; Roberto Wiener; Steve Roux; Ryan Munden

doi:10.1117/12.2584772

22 February 2021 Frequency encoding scheme for reticle front and back side inspection

Michal E. Pawlowski, Corey Loke, Aage Bendiksen, Peter Kochersperger, Roberto Wiener, Steve Roux, Ryan Munden

Proceedings Volume 11611, Metrology, Inspection, and Process Control for Semiconductor Manufacturing XXXV; 116110O (2021) https://doi.org/10.1117/12.2584772
Event: SPIE Advanced Lithography, 2021, Online Only

Abstract

EUV and DUV reticles are inspected before exposure to guarantee the quality of the lithographic process. The pellicle and the reticle back side are typically inspected for the presence of contaminants which are several micrometers in diameter. While detection of macroscopic particles is fairly straightforward, delineation between particle and stray light due to diffractive properties of reticle pattern is challenging. We present a particle detection system based on structural illumination technology capable of automatic delineation between contaminants and stray light. During measurement a series of images is acquired by a macro-imaging optical detector (e.g. camera) positioned normal in reference to the investigated sample. The surface under test is illuminated at an oblique angle by an incoherent polychromatic projection system projecting a pattern whose temporal frequency changes across the inspected surface. The signal acquired by the detector is in general an incoherent sum of light scattered by particles with stray light returned by the diffractive pattern. Temporal samples of intensity data are analyzed pixel by pixel in the Fourier domain and the particles are differentiated from the stray light by comparing the Fourier spectra of the acquired signal with the frequency a particle should generate at an analyzed pixel based on the system geometry. Thus, unwanted stray light signal contributions are separated from particle signal by performing logical operations on the signal in the Fourier domain. Experimental results from a technology demonstrator are provided to illustrate performance.

Conference Presentation

Citation Download Citation

Michal E. Pawlowski, Corey Loke, Aage Bendiksen, Peter Kochersperger, Roberto Wiener, Steve Roux, and Ryan Munden "Frequency encoding scheme for reticle front and back side inspection", Proc. SPIE 11611, Metrology, Inspection, and Process Control for Semiconductor Manufacturing XXXV, 116110O (22 February 2021); https://doi.org/10.1117/12.2584772

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