A Model for Comprehensive Studies of porosity in Mesoporous Low-K Dielectrics
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A Model for Comprehensive Studies of Porosity in Mesoporous Low-K Dielectrics
Mihail P. Petkov Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, U.S.A.
ABSTRACT The successful integration of a porous low dielectric constant (k) material as an interlevel dielectric depends on the morphology of the embedded porosity. Simple site percolation models are utilized here to investigate porosity properties of low-k dielectrics with respect to the current technology trends. Significant differences between two generations of porous dielectrics, k < 2.4 and k < 2.1, are found. The porosity fraction in the latter is above the percolation threshold, which may have serious impact on the materials physical properties and its compatibility with production steps.
INTRODUCTION Historically, the performance of electronic devices has been improved by miniaturizing the devices, which lowered the transistor gate delays. However, the signal propagation delay (RC delay; R – metal resistance, C – dielectric capacitance) became the dominant factor to-date, and future advances rely on overcoming the materials limitations. For this end, Cu instead of Al interconnects are already used in state-of-the-art devices, and low dielectric constant (low-k, k < 2.7) materials are sought to substitute the SiO2 as interlevel dielectrics (ILD’s). Companies are adopting different strategies for this transition; however, most of them will use low-k dielectrics for the 0.13 µm node [1]. Next-generation technologies will require ultra-low-k ILD’s with effective k < 2.1, which must incorporate porosity (k ≈ 1). Manufacturable ultra-low-k solutions are not presently known [2]. The integration of the low-k materials faces many problems [1]. In comparison with SiO2, lower k values are achieved at the expense of a spectrum of other properties, such as hardness, strength, thermal conductivity, adhesion, metal diffusion, etc. They will be further compromised by the presence of porosity, and the compatibility with some production steps will be severely degraded. Thus, understanding the role of the porosity morphology on the characteristics of the materials is important for the successful integration of any low-k material as ILD. Computer-based models built on percolation theory [3-5] are especially suitable for studies of porous materials. They have been successfully utilized in diverse areas, such as micro-fluidics, selective catalysis, molecular separation, chemical sensing, electro-optics, and microelectronics. In this work, simple models are utilized in a qualitative investigation of the relationship between the morphology of the porosity and the technology requirements given in the International Technology Roadmap for Semiconductors (ITRS) [2].
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