CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics
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CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics P. Ryan Fitzpatrick1, Sri Satyanarayana2, Yangming Sun3, John M. White3, and John G. Ekerdt1 1 Department of Chemical Engineering, University of Texas, Austin, TX 78712 2 SEMATECH, Austin, TX 78741 3 Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712 ABSTRACT Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ. INTRODUCTION As efforts continue to scale down integrated circuits to the 45 nm node, resistivecapacitive (RC) delay in copper interconnect layers is an issue that must be addressed. Ultra low-k (ULK) porous dielectrics are one potential solution to achieving the desired metal pitches without exceeding the RC delay set forth by the International Technology Roadmap for Semiconductors [1]. However, porous ULK dielectrics are susceptible to metallic precursor infiltration during the deposition of conducting diffusion barriers [2, 3]. This occurrence alters the electrical properties of the film, ultimately resulting in increased RC delays or an electrical short between neighboring interconnects. The International Union for Pure and Applied Chemistry (IUPAC) classifies the porosity of solids as either microporous (pore diameters less than 2 nm) or mesoporous (pore diameters between 2 and 50 nm) [4]. Furthermore the same dimensions can be used to define whether a dielectric’s pores are microconnected or mesoconnecte
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