In-situ Optical Characterization of Noble Metal Thin Film Deposition and Development of a High-performance Plasmonic Sensor

TL;DR

This paper introduces a novel in-situ optical characterization method using tilted fiber Bragg grating sensors for real-time monitoring of noble metal thin film deposition processes, especially gold, with high sensitivity for plasmonic sensor development.

Contribution

It presents the first application of TFBG sensors for in-situ, real-time characterization of CVD and ALD processes for noble metals, enabling enhanced process monitoring and sensor development.

Findings

Effective optical property characterization of ultrathin gold films.

Demonstrated in-situ monitoring of ALD processes for gold and Al2O3.

Achieved high refractometric sensitivity (~550 nm/RIU) in plasmonic sensors.

Abstract

The present work addressed in this thesis introduces, for the first time, the use of tilted fiber Bragg grating (TFBG) sensors for accurate, real-time, and in-situ characterization of CVD and ALD processes for noble metals, but with a particular focus on gold due to its desirable optical and plasmonic properties. Through the use of orthogonally-polarized transverse electric (TE) and transverse magnetic (TM) resonance modes imposed by a boundary condition at the cladding-metal interface of the optical fiber, polarization-dependent resonances excited by the TFBG are easily decoupled. It was found that for ultrathin thicknesses of gold films from CVD (~6-65 nm), the anisotropic property of these films made it non-trivial to characterize their effective optical properties such as the real component of the permittivity. Nevertheless, the TFBG introduces a new sensing platform to the ALD and CVD community for extremely sensitive in-situ process monitoring. We later also demonstrate thin film growth at low (<10 cycle) numbers for the well-known Al2O3 thermal ALD process, as well as the plasma-enhanced gold ALD process. Finally, the use of ALD-grown gold coatings has been employed for the development of a plasmonic TFBG-based sensor with ultimate refractometric sensitivity (~550 nm/RIU).