Advancing the Industrialization of Thin Film Deposition: Tools for Mitigating Powder Formation in Spatial-ALD Systems and for Real-time, In-situ Metrology

Abstract

Thin-film manufacturing through Spatial Atomic Layer Deposition (SALD) offers high throughput and cost-saving advantages, but challenges such as powder formation and the lack of real-time in-situ metrology hinder its industrial-scale viability. This thesis focuses on improving the reliability of the SALD process in two key ways: mitigating the powder formation in SALD systems which tends to diminish film quality and identifying in-situ metrology techniques to assure the quality of SALD films. The first section investigates the influence of deposition variables, including precursor concentration, reactor-substrate gap spacing, and temperature, on powder formation. A novel powder quantification module, based on exhaust filter resistance measurements, enables systematic investigation of these parameters. This approach was used to identify optimal parameters for minimizing powder (e.g., Gap = 0.5mm, Curtain > 4000 SCCM, Temperature > 100°C). Additionally, a method to assess SALD precursor isolation, a critical factor in reducing powder formation, is introduced. These quantification methods represent a significant step toward reducing powder in industrial SALD systems as there have been few attempts at systematically quantifying the effects of deposition conditions on powder formation. In the second section, three metrology techniques (Absorbance spectroscopy, reflectometry, and ellipsometry) are evaluated for their efficacy in measuring SALD-produced films. These techniques are evaluated using Al2O3- and ZnO-coated flexible PLA samples. This study finds that while absorbance was effective in measuring small ZnO thicknesses (12 nm-85 nm), it could not be used for Al2O3 films. We also found that while small film thicknesses were discernable with both ellipsometry and reflectometry raw data, generating models to calculate thickness would not be straightforward. This work demonstrated that ellipsometry modelling would need to incorporate substrate orientation and reflectometry modelling would need to incorporate refraction through multiple films. Overall, this thesis contributes significant insights into overcoming key obstacles in the industrialization of the SALD process, offering practical solutions for powder reduction and film quality assurance.