Fracture Property Improvements of a Nanoporous Thin Film via Post Deposition UV Curing
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0914-F01-07
Fracture Property Improvements of a Nanoporous Thin Film via Post Deposition UV Curing Jeannette M. Jacques, Ting Y. Tsui, Andrew J. McKerrow, and Robert Kraft Silicon Technology Development, Texas Instruments, Inc., Dallas, Texas, 75243
ABSTRACT As silicon-based microelectronic devices continue to aggressively scale down in size, traditional BEOL dielectric materials have become obsolete due to their relatively high dielectric constant. Organosilicate glass (OSG) materials have emerged as the predominant choice for intermetal dielectrics in advancing technology nodes. A potential failure mechanism for this class of low-k dielectric films during the manufacturing process is catastrophic fracture due to channel cracking. To improve the mechanical strength and stability of these silicon-based materials, the use of post-deposition curing processes is under evaluation. In this work, the effects of UV curing on the properties of OSG films were characterized. After UV curing, film hardness and elastic modulus are improved, with no change in the residual film stress. The average film density increases linearly as a function of UV exposure time. Channel crack propagation velocities decrease with UV exposure. The improvements in the mechanical properties of OSG films are believed to correlate with the increasing Si-O-Si bond population. Comparisons between post-deposition UV and Electron Beam curing processes are provided. INTRODUCTION The incorporation of low-k dielectric films is necessary to improve semiconductor device performance. Organosilicate glass (OSG) materials are the primary candidates for advanced intermetal dielectrics. A potential cohesive failure mechanism of OSG films is catastrophic failure due to channel cracking. The driving force for channel cracking is dependent on several material properties, including plane strain modulus, density, and residual film stress. 1, 2 Efforts to improve the mechanical strength of these materials face many challenges, including the need to maintain a low dielectric constant. The use of post-deposition bond modification processes, such as electron beam (EB) and ultra-violet (UV) curing, has been investigated to overcome the difficulties presently facing OSG materials. Recent studies have detailed the use of EB curing for hybrid dielectric structures, 3, 4 as well as individual OSG layers. 5 Superior structural reliability and electrical performance were reported for samples receiving EB curing. 3-5 In these studies, the effects of UV curing on the properties of individual OSG films are characterized. Comparisons between the effects of EB and UV curing on OSG materials are provided. EXPERIMENTAL CONDITIONS PECVD techniques were utilized to deposit k ~ 2.6 OSG films onto 200 mm (100) silicon wafers via an octamethylcyclotetrasiloxane (OMCTS) precursor. All deposited films were 1.3
µm in thickness. A commercial UV light source was used to cure these films at 400oC. UV exposure times ranged from 0 to 7 minutes. No capping materials were present during curing. Str
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