PECVD low-permittivity organosilicate glass coatings: Adhesion, fracture and mechanical properties Youbo Lin a , Yong Xiang a , Ting Y. Tsui b , Joost J. Vlassak a, * a School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA b Department of Chemical Engineering, Nanotechnology Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ont., Canada N2L 3G1 Received 11 January 2008; received in revised form 19 April 2008; accepted 4 June 2008 Available online 3 July 2008 Abstract The structure and mechanical behavior of organosilicate glass (OSG) coatings have been analyzed as a function of composition and UV irradiation time. A decrease in the OSG carbon content results in more networking bonds and increased connectivity; UV irradiation increases the connectivity by severing weak terminal bonds and stabilizes the network through local bond rearrangements. These struc- ture modifications lead to a significant improvement in the stiffness, hardness, and fracture energy of these coatings. The networking bond density and mean connectivity number correlate well with the mechanical behavior of the OSG films, although network bond den- sity weighted by bond energy is a more appropriate measure. The adhesion energy of silicon nitride to OSG is significantly higher than the cohesive energy of the OSG as a result of interface densification and crack-tip shielding. Subcritical fracture measurements in aque- ous environments show that the detrimental effect of water on adhesion surpasses the effect of network connectivity. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Low-permittivity; Organosilicate glass; Thin film; Mechanical properties; Fracture 1. Introduction As the microelectronics industry strives to manufacture high-performance integrated circuits at lower cost, new materials are introduced to meet the evermore-stringent requirements raised by the shrinking feature size. Dielectric materials with low permittivity, primarily organosilicate glass (OSG) fabricated with plasma-enhanced chemical vapor deposition (PECVD) technologies, are employed to replace conventional silicon dioxide as the inter-metal insu- lator. These new materials are necessary to reduce the interconnect delay and power dissipation associated with the capacitive coupling between closely placed copper wires. Fully dense OSG has a bulk dielectric constant that is tunable from 2.8 to 3.3, and is currently used in the pro- duction of advanced integrated circuits. However, to meet the requirements for future technology nodes, the dielectric constant needs to be reduced even more and this requires the introduction of porosity into the OSG coatings [1]. The low dielectric permittivity of OSG as compared to silica is attributed primarily to its lower density, which results from the disruption of the silicon dioxide network by terminal organic groups (mostly methyl groups) [2,3]. Introduction of these organic groups lowers the dielectric constant k at the expense of the mechanical integrity of the material, making it a challenge to integrate these dielec- trics without causing reliability issues such as delamination and cracking during or after manufacturing [4]. Hence it is important to optimize the mechanical properties of OSG coatings through a good understanding of the relationship between film matrix structure and mechanical behavior, especially if porous films are to be used [5]. In this study, we try to shed light on this relationship by measuring the mechanical response of a series of OSG films and by correlating this response with the network structure of the films. In a recent paper, we presented a systematic analysis of the composition, structure and 1359-6454/$34.00 Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2008.06.007 * Corresponding author. E-mail address: vlassak@esag.harvard.edu (J.J. Vlassak). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 56 (2008) 4932–4943