Effects of ultraviolet radiation on ultra-low-dielectric constant thin film fracture properties
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Ting Y. Tsui Department of Chemical Engineering, Nanotechnology Institute, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
Paul S. Ho The Laboratory for Interconnect and Packaging, The University of Texas at Austin, Austin, Texas 78758 (Received 25 March 2009; accepted 12 June 2009)
The effects of ultraviolet (UV) radiation on ultra-low-k dielectric (ULK) thin film fracture toughness were studied. This work discusses both critical and subcritical crack growth behavior under different environments. The critical fracture toughness was measured as a function of applied phase angle by using the four-point bend flexure and mixed-mode double cantilever beam techniques. Results of critical fracture toughness obtained under different loading configurations and phase angles were found to increase with the UV treatment time. In contrast, mode I subcritical fracture toughness thresholds and the crack propagation velocity appeared to be insensitive to UV curing processes. This study revealed that subcritical fracture toughness values reduced with the moisture concentration in the environment.
I. INTRODUCTION
This work investigated the effects of postdeposition ultraviolet (UV) radiation curing on molecular structures and mechanical properties of porous organosilicate glass (p-OSG) thin films. These thin films are commonly used in the high-performance integrated circuits as ultra-low dielectric constant materials to reduce the capacitance delay between copper interconnect lines. P-OSG consists of two components, nanometer-scale pores and a silicon oxide matrix with methyl, hydroxyl, or hydrogen termination groups. The film porosity can be controlled to greater than 20%. To generate these pores, aromatic ring organic molecules are added to the precursors during plasma-enhanced chemical vapor deposition (PECVD) processes. These organic molecules can be vaporized by the postdeposition UV treatment process leaving nanometer-scale pores. In our complementary study,1 the effects of UV curing on p-OSG molecular structures and electrical properties have been reported. The key results showed that the network silica and suboxide bonds increased at the expense of methyl and hydroxyl groups during the (UV) curing process. In this report, the effects of UV radiation on the fracture behaviors of the ultra-low-k films will be discussed in detail. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0346 J. Mater. Res., Vol. 24, No. 9, Sep 2009
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Cohesive and adhesive failures of UV radiated dielectric materials have been studied by Iacopi et al.,2 Gage et al.,3 Lin et al.,4 and Kim et al.5 Iacopi et al.2 investigated the radiation effects on the fracture behavior of high-density OSG materials with 7% porosity and k-value of 3.0. These materials were used for the older 65-nm technology nodes. Gage et al.3 observed that the UV cure process increased the low-k materials four-point bend flexure (4-pt bend) fracture toughness. H
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