Ultra Low-dielectric-constant Materials for 65nm Technology Node and Beyond
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Ultra Low-dielectric-constant Materials for 65nm Technology Node and Beyond Hao Cui, Darren Moore, Richard Carter, Masaichi Eda, Peter Burke LSI Logic Corporation, 23400 NE Glisan St., M/S AR-220, Gresham, OR 97030, U.S.A. David Gidley and Huagen Peng Department of Physics, University of Michigan, Ann Arbor, MI 48109, U.S.A ABSTRACT Pore characteristics including pore size distribution, porosity, and pore interconnectivity of PECVD SiCOH inter- layer dielectric (ILD) materials with different dielectric constant (κ) values have been studied. Oxygen plasma damage to SiCOH low-κ films increases dramatically as the κ value decreases. Simulations showed that, compared to the ILD film, the overhead dielectric films have a significant impact on the overall effective κ (κeff )of the BEOL interconnects. Reducing the κ values of these overhead films helps to alleviate the pressure on the κ value requirement of the ILD materials while still meeting the κeff target. Ultra low-κ (ULK) PECVD hydrogenated silicon carbide (H:SiC) films with a κ of 3.0 have been studied for the etch-stop applications. Studies of the chemical composition and bonding structure suggest that less Si- C networks are formed and more micro-porosity are incorporated in the ULK H:SiC film. The leakage current of the ULK H:SiC film is found to be about 5 times lower than the H:S iC and H:SiCN films with higher κ values. The etch rate of ULK H:SiC film using a standard SiCOH ILD etch chemistry has been found to be negligible. Such an extremely high etch selectivity makes these films very good etch-stop layers. INTRODUCTION As ultra- large scale integrated circuit (ULSI) technology advances, low-κ dielectric materials are needed for ULSI interconnect applications to address the increasingly significant interconnect-related issues including interconnect delay, dynamic power consumption and crosstalk noise. Evident from the history of the International Technology Roadmap for Semiconductor (ITRS) projections, the implementation of low-κ materials has been continuously pushed out [1]. For example, the technology node where low- κ materials with a κeff of about 2.0 were projected to be implemented has been pushed out from the 90 nm node in the 1999 ITRS to the 32 nm node in the 2003 ITRS [1]. Such a delay has been caused by the revelations of substantial process and reliability challenges as researchers and engineers started to evaluate and integrate materials with lower κ values. The dielectric constant is a physical measure of how easy a material can be polarized in an external electric field. The quantitative relation between the dielectric constant and properties of the atoms and molecules of the material is described by the Clausius-Mossotti equation ε r −1 1 = N jα j [1] ε r + 2 3ε 0 ∑ j where ε r is the dielectric constant, Nj and α j the volume density and polarizability of the j th type of atom or molecule. The symbol κ, which has been adopted by the VLSI industry to represent the dielectric constant, will be used in the discussions of this work. As
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