Surface roughness of waveguide sidewalls measured by AFM

• Published in: Proceedings of SPIE, the international society for optical engineering Vol. 13414; pp. 134140A - 134140A-4
• Main Authors: Kocun, Marta, Ren, Zhong
• Format: Conference Proceeding
• Language: English
• Published: SPIE 21.03.2025
• ISBN: 1510686061; 9781510686069
• ISSN: 0277-786X
• DOI: 10.1117/12.3040075

Waveguide structures are essential components of optical architectures for AR/MR/VR devices therefore, significant effort is put into their design and manufacturing. Material type, surface geometry, and feature size, all need to be carefully considered to achieve the desired waveguide performance. Specifically, waveguide efficiency strongly depends on surface topography and surface roughness, which makes quantitative characterization of these properties necessary. Deep reactive ion etching (DRIE) and plasma polishing processes are indispensable to produce high-quality, high aspect ratio structures with extreme precision of critical dimensions. Ensuring smooth sidewalls through optimized plasma polishing is vital because sidewall roughness can significantly impact the deposition of functional materials, leading to potential degradation in device performance. Smooth sidewalls are also essential for maintaining the integrity and functionality of the deposited materials, which ultimately ensures efficient device operation. Traditional scanning electron microscopy (SEM) has limitations in measuring surface roughness on etched sidewalls due to the high aspect ratios and surface charges associated with these structures. As a result, alternative characterization techniques are necessary to accurately measure sidewall roughness, thereby ensuring the highest possible quality and performance of the etched structures. Atomic Force Microscopy (AFM) imaging is a nondestructive, surface characterization technique that is performed in ambient conditions with minimal sample preparation. Here we present how DRIE and plasma polishing processes are used to prepare high aspect ratio structures, such as vias and waveguides, and how AFM imaging is used to monitor changes in topography and sidewall surface roughness of these features throughout the processing cycle.