Subcritical Delamination of Dielectric and Metal Films from Low-k Organosilicate Glass (OSG) Thin Films in Buffered pH S
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Subcritical Delamination of Dielectric and Metal Films from Low-k Organosilicate Glass (OSG) Thin Films in Buffered pH Solutions Y. Lin1, J.J. Vlassak1, T.Y. Tsui2, and A.J. McKerrow2 DEAS, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA 2 Silicon Technology Development, Texas Instruments Inc., Dallas, TX 75243, USA
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ABSTRACT Understanding subcritical fracture of low-k dielectric materials and barrier thin films in buffered solutions of different pH value is of both technical and scientific importance. Subcritical delamination of dielectric and metal barrier films from low-k organosilicate glass (OSG) films in pH buffer solutions was studied in this work. Crack path and subcritical fracture behavior of OSG depends on the choice of barrier layers. For the OSG/TaN system, fracture takes place in the OSG layer near the interface, while in OSG/SiNx system, delamination occurs at the interface. Delamination behavior of both systems is well described by a hyperbolic sine model that had been developed previously based on a chemical reaction controlled fracture process at the crack tip. The threshold toughness of both systems decreases linearly with increasing pH value. The slopes of the reaction-controlled regime of the crack velocity curves for both systems are independent of pH as predicted by the model. Near transport-controlled regime behavior was observed in OSG/TaN system. INTRODUCTION Organosilicate glass (OSG) is one of the leading low-k dielectric materials for use as an interlayer dielectric (ILD) in high-performance interconnects. Due to the incorporation of organic groups (e.g., -CH3), the structure and surface chemical state of the OSG films are very different from those of conventional SiO2. One of the main issues that arise when integrating low-k dielectric materials into a standard microfabrication process is the relatively poor adhesion between low-k dielectric materials and barrier layers. When subjected to stress in a chemically reactive environment, such as during chemical-mechanical polishing (CMP) or dicing, stress corrosion cracking can cause delamination of the barrier films. Although subcritical cracking of bulk silicate glass has been investigated [1], it is not well understood how the chemical agents in the environment affect subcritical fracture of barrier/low-k thin films structures. Here we report, for the first time, experimental results on subcritical cracking of OSG/TaN and OSG/SiNx films in buffered pH solutions. These data were fitted and analyzed with a Sinh model developed previously [2-4]. EXPERIMENTAL Subcritical delamination tests were conducted by means of the four-point bending technique. The detailed sample preparation technique and test procedures are described elsewhere [3]. Briefly, 500 nm OSG films with a dielectric constant of ~ 2.8 were grown on silicon wafers using a PECVD process. Subsequently, 80 nm SiNx barrier films were deposited on top of the OSG films followed by a sputtered 40 nm Ti/400 nm Cu shielding layer. TaN/OSG films were
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