Straightforward method for sidewall roughness measurements by AFM on ion beam etched slanted diffraction gratings and their topography development

Paulo Lima; Sebastien Pochon; David Pearson; Sung-Jin Cho

doi:10.1117/12.3000170

12 March 2024 Straightforward method for sidewall roughness measurements by AFM on ion beam etched slanted diffraction gratings and their topography development

Paulo Lima, Sebastien Pochon, David Pearson, Sung-Jin Cho

Author Affiliations +

Proceedings Volume 12913, Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR) V; 129131A (2024) https://doi.org/10.1117/12.3000170
Event: SPIE AR | VR | MR, 2024, San Francisco, California, United States

Conference Poster

Abstract

The roughness of sidewalls on slanted etched diffraction gratings needs to be minimized to avoid compromising their optical efficiency. Sidewall roughness usually does not significantly alter the overall features of gratings reflectance, however, narrow spectral features that are due to strong Fabry–Perot resonances can be strongly affected by roughness1,2. The complication in performing these roughness measurements is to access the slanted sidewall by Atomic Force Microscope (AFM) tips on a typical etched feature with Critical Dimension (CD) of 100 nm, 200 nm pitch and on a steep angle of 45 degrees. Usually, to address this challenge, expensive long AFM tips and non-standard AFMs capable of measuring samples on a certain angle are used2. Alternatively, a post process on the wafer is required3,4,5. We present a simple method to measure the gratings’ sidewall roughness without any physical and/or chemical process and optical analysis needed before or after the measurement and which is also done on a standard AFM. The method could, in principle, be applied to measure sidewall roughness on any etched trench sidewalls or deposited features. Diffraction gratings were processed by an Oxford Instruments Plasma Technology’s Large (30cm) Ion Beam Etch Source. Patterned SiO2 and Silicon slanted sidewalls roughnesses were measured by an in-house conventional Asylum Research - Jupiter XR - AFM allowing a speedy sidewall roughness assessment and development. Feasibility tests for SiO2 slanted diffraction gratings processed by the Oxford Instruments Plasma Technology Ion Beam Etch System showed a very low roughness of 1.3nm for the trench sidewall.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Paulo Lima, Sebastien Pochon, David Pearson, and Sung-Jin Cho "Straightforward method for sidewall roughness measurements by AFM on ion beam etched slanted diffraction gratings and their topography development", Proc. SPIE 12913, Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR) V, 129131A (12 March 2024); https://doi.org/10.1117/12.3000170

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