Stress corrosion of organosilicate glass films in aqueous environments: Role of pH
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C. Elia Inter-university Micro-Electronics Center (IMEC), Kapeldreef 75, B-3001 Leuven, Belgium; and Istituto Universitario degli Studi Superiori di Pavia, Pavia, Italy
T. Fournier Inter-university Micro-Electronics Center (IMEC), Kapeldreef 75, B-3001 Leuven, Belgium; and Génie des Matériaux, Université Aix-Marseille III, Marseille, France
F. Sinapi and Y. Travaly Inter-university Micro-Electronics Center (IMEC), Kapeldreef 75, B-3001 Leuven, Belgium (Received 27 May 2007; accepted 2 January 2008)
Subcritical cracking of thin glass films caused by stress-corrosion phenomena cannot be neglected when it comes to application and manufacturing processes that involve exposure to aqueous environments. A protocol is introduced to allow for a quantitative study of stress corrosion through channel cracking experiments. By this method, an exponential dependence of the crack propagation rate on the pH of the aqueous environment is revealed. Therefore, this behavior should be accounted for through the use of an appropriate pre-exponential factor in the expression of channel cracking rate. This factor should reflect the reduced crack resistance of the glass film caused by the weakening of the silica bonds behind the crack tip in the aqueous environment. A direct comparison between commercial slurries and reference solutions confirms that the crack resistance is a function of the pH of the ambient.
I. INTRODUCTION
In recent years the microelectronics community has focused its attention on alternative materials to comply with the requirements given by the dramatic downscaling of feature sizes. One example is organosilicate glasses (OSGs) or carbon-doped silicon oxides, known as lowdielectric-constant (“low-k”) materials.1 The use of these dielectrics as a replacement for SiO2 in interconnects technology reduces the dynamic power consumption and parasitic resistance-capacitance (RC) delay.1 The silica bond chains of organosilicate glasses are terminated by –CH3 hydrophobic groups. This leads to a net decrease in density and polarizability of the silica matrix and thus to a lower dielectric constant than SiO2. To decrease the dielectric constant even further, large amounts of porosity (up to 50% of the volume) can be incorporated into the OSG films. The introduction of porosity deteriorates the mechanical properties of the organosilicate films. The Young’s modulus and the hard-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0108 862 J. Mater. Res., Vol. 23, No. 3, Mar 2008 http://journals.cambridge.org Downloaded: 19 Mar 2015
ness of such films decrease abruptly as film porosity increases.2 Cohesive strength of such films is also dramatically affected by the reduction of bond density. The worsening of mechanical properties of porous OSG films, combined with intrinsic stresses generated during the growth of the films and with stresses generated by mechanical loads during interconnects manufacturing processes2,3 such as thermal cycles or chemical– mechanical polishing pro
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