Ellipsometric Measurements in Thin Film Coating Processes using a Polarization Camera

Abstract

The physical vapor deposition (PVD) process for thin film fabrication is challenging to monitor in-situ using conventional techniques. The vacuum environment required for the process to work necessitates a hermetic seal, limiting observation to viewing through small portholes in the reactor hull. To address these limitations, we propose a novel monitoring approach employing a polarization camera, enabling enhanced thin film characterization and process monitoring despite the restricted optical access. In this approach, the inherent polarimetric capabilities of the camera are complemented by ellipsometric approximations, leveraging optical physics principles to analyze the growth dynamics of the deposited film and assess its quality. Ellipsometry is an optical technique that measures changes in the polarization state of light reflected from a surface, providing sensitive information about film thickness, refractive index, and other material properties. Typically, thin film characterization is performed using expensive, off-the-shelf ellipsometry systems, which require the coating process to end first, in order to retrieve and then physically transfer the coated sample to a dedicated measurement station. While various imaging-based ellipsometry methods have demonstrated promising results, our approach reduces cost and setup complexity by employing approximate calculations and limited hardware. Although this results in lower accuracy compared to traditional systems, the approximations remain sufficiently reliable for the objectives of this project and the laboratory that commissioned it. Our experiments demonstrate that film growth, stagnation, and even damage to the film can be effectively detected, enabling fine-tuning of process parameters for economic reasons and timely process termination in the case of damage. Furthermore, by employing fitting simulations, we were able to accurately estimate refractive properties of the film, thereby validating our system and arguably enabling deeper material classification. An additional effort to simulate the reactor environment produced polarization parameters nearly identical to our measured data, providing strong validation and plausibility for our experimental results.

Date of Award	2025
Original language	English
Supervisor	Gerald Zauner (Supervisor)