Effect of humidity on the residual stress in silicon-containing plasma polymeric coatings

• Published in: Surface & coatings technology Vol. 347; pp. 46 - 53
• Main Authors: Top, Michiel, Mulder, Guus, Prager, Nicole, Fahlteich, John, De Hosson, Jeff Th.M.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.08.2018; Elsevier BV
• Subjects: Arc deposition; Carbon content; CHE; Chemical vapor deposition; Coating effects; Compressive properties; Contact angle; Electric arcs; HMDSO; Hollow cathodes; Humidity; Hygroscopic expansion; Inorganic coatings; PECVD; Polymer coatings; Polymer films; Polymers; Protective coatings; Relative humidity; Residual stress; Silicon dioxide; Substrates; Thermal expansion; Thin film coatings; Thin films; HMDSO; CHE; PECVD; Hygroscopic expansion; Residual stress
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.04.066

Residual stress measurements of thin films are common practice in device technology and are extremely important in particular for the characterization of thin film coatings. A largely ignored stress contribution is the difference in coefficient of hygroscopic expansion between the coating and substrate. This paper presents a rather novel approach to accurately evaluate the residual stress and coefficient of hygroscopic expansion of strongly curved specimens. Silicon-containing plasma polymer coatings with different carbon contents were deposited using hollow cathode arc discharge based PECVD. Samples of different layer composition were produced comprising silicon-containing plasma-polymer layers with a high carbon concentration and more “inorganic” SiO2 like layers with lower carbon concentration. All coatings show a compressive stress state. The highest stress was measured in the coating with the highest carbon content (239 ± 6 MPa) and decreases to 94 ± 31 MPa at lower carbon contents. Variation of the humidity showed that all coatings expand under influence of increasing relative humidity. The most inorganic coatings exhibits the highest expansion coefficient of 29.2 ± 2·10−6 (% r.h.)−1. The results obtained were compared with the results from contact angle measurements. An increase in the hygroscopic expansion corresponds with an increasing hydrophilicity of the coatings. •Silicon-containing plasma polymeric coatings expand under increasing humidity.•More organic coatings show lower expansion under increased relative humidity.•The relative humidity influences the residual stress state up to 22%.