The effects of low temperature and pressure on the fracture behaviors of organosilicate thin films
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Steven A. Vitale Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420-9108
Ting Y. Tsuia) Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, CANADA (Received 25 February 2011; accepted 3 August 2011)
A novel load–displacement sensing instrument has been designed and fabricated to characterize the fracture properties of brittle thin films at low temperature (approximately 30 °C) and pressure (1.6e-4 Pa) environments. In this study, the instrument was used to investigate the effects of harsh environments on the fracture behaviors of organosilicate glass (OSG) and silicon carbonitride (SiCN) thin films under four-point bend loading. Experimental results showed that the fracture strengths of film stacks are the highest when the environment contains a very low water molecule concentration. This condition can be achieved by purging the testing chamber with pure nitrogen or reducing the chamber pressure to less than 1 Pa. In contrast, cracks propagated readily along OSG/SiCN interfaces when experiments were performed in deionized water. The effects of low temperature (approximately 30 °C) and pressure on thin film fracture were also studied, and the results demonstrated that there is no observed degradation of the OSG fracture properties. X-ray photoelectron spectroscopy (XPS) technique was used to identify the chemical composition of the fracture surfaces.
I. INTRODUCTION
High performance integrated circuit (IC) back-endof-line (BEOL) structures are constructed with copper interconnect lines and low-dielectric constant (k) insulators to reduce resistive and capacitive delay. These low-k thin films are composed of amorphous silicon dioxide; however, some of the bridging oxygen atoms are replaced with hydrogen or hydroxyl groups and by organic groups such as methyl (-CH3) or methylene (-CH2-). These hybrid organic–inorganic materials are often referred to as organosilicate glass (OSG). To further reduce the dielectric constant of the OSG and achieve k values as low as 2.6 to 2.3, nanometer scale pores are often introduced into the matrix creating porosity in the range of ;7 to ;45%.1–3 In a well hermetically sealed IC product with a protective overcoat, such as silicon nitride, these nanopores are evacuated with the internal pressure defined by the deposition steps during the IC manufacturing processes. The increase of porosity within the OSG molecular structure reduces the average bond density and weakens the mechanical strength of these materials, thereby increasing their vulnerability to stress corrosion cracking and inducing catastrophic failure. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.253 2524
J. Mater. Res., Vol. 26, No. 19, Oct 14, 2011
http://journals.cambridge.org
Downloaded: 01 Apr 2015
Environmental effects on the fracture properties of bulk glass materials, such as amorphous silica and borosilicate glass, have been thoroughly studied.4–9 A reaction-rate-controlled model to predict
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