Organosilicate glass (OSG) materials have emerged as the predominant choice for intermetal dielectrics in advancing technology nodes of 90 nm and beyond. A potential failure mechanism for this class of low-k dielectric films during the manufacturing process is catastrophic fracture due to channel cracking. The driving force for channel cracking is dependent upon several film properties, including the plane strain modulus, volumetric density, and residual stress. To improve the mechanical strength and stability of these silicon-based materials, the use of post-deposition curing processes is under evaluation. Within this work, the effects of UV curing upon the structure and mechanical properties of OSG films were characterized. Data are reported for a set process temperature of 400oC and UV exposure times ranging from 0 minutes to 7 minutes. OSG thin films were deposited on bare (100) silicon wafers at a thickness of 1.3 μm and k value of 2.6 via plasma enhanced chemical vapor deposition. Nano-indentation measurements were conducted at a depth of 68.5 nm, representing less than 10% of the total film thickness and therefore minimizing any potential substrate effects. After UV curing, film hardness and elastic modulus are improved according to power law functions, with no measurable increase in the residual tensile film stress. For a UV exposure time of 5 minutes, the film hardness increased by approximately 26% and the resultant elastic modulus increased by 47%. The average film density, as determined by Rutherford Backscattering analysis, was observed to increase linearly as a function of UV exposure time. The average volumetric film density rose by 5% in specimens cured for 5 minutes, correlating well with measured film shrinkage data. Channel crack propagation velocities were observed to decrease as a power law function of UV exposure time. The UV cure process facilitates a 2.5 order of magnitude decrease in channel cracking rates, as compared to as-deposited OSG films. Crack susceptibility is only improved by a factor of 4X when the UV exposure time is increased from 3 minutes to 7 minutes. FTIR spectral analysis was used to characterize structural molecular film changes as a result of the UV cure process. The Si-O-Si bond population was observed to increase as a function of UV exposure time, however, the ratio of individual bond types within the spectral band was not altered. The area of the Si-O-Si band increased by 9% after UV curing for 7 minutes, as compared to uncured films. No measurable changes in the Si-H or Si-(CH3)X bond populations resulted from UV curing. The improvements in the mechanical properties of these OSG thin films are believed to correlate with the increasing Si-O-Si bond population. Si-O bonds are the most robust structures comprising OSG materials and can have a significant impact on mechanical stability. Comparisons between post-deposition UV and Electron Beam curing processes are also provided.
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