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Achieving ultra low k dielectric constant for nanoelectronics interconnect systems

: Schulz, S.E.; Schulze, K.


Tang, T.-A. ; IEEE Electron Devices Society:
8th International Conference on Solid-State and Integrated Circuit Technology, ICSICT 2006 : Oct. 23 - 26, Shanghai, China; proceedings
Piscataway, NJ, USA: IEEE Press, 2007
ISBN: 1-4244-0161-5
ISBN: 978-1-4244-0161-1
International Conference on Solid-State and Integrated Circuit Technology (ICSICT) <8, 2006, Shanghai>
Fraunhofer IZM ()
Fraunhofer ENAS ()

Air gaps are a promising alternative to porous low-k dielectrics to achieve ultra low k-values in Cu damascene interconnects. Two approaches of air gap formation using wet etch back of sacrificial PECVD SiO2 dielectrics were evaluated concerning their feasibility and preparation results are shown. Electrical measurements were verified by simulation and have shown a capacitance reduction of approximately 50 % compared to the SiO2 filled reference structures. Furthermore finite element method (FEM) simulations were performed to extract the effective k-value for different technology nodes. General keff extraction procedure by FEM simulation is described. Furthermore the impact of variation of thickness and k-value of the functional layers applied for air gap formation was investigated. These functional layers are etch stop, cap and mask layers and currently consist of PECVD SiC:H films. It has been shown, that both parameters (thickness and k-value) considerably contribute to the effective k-value. For both investigated technology nodes, the 65 nm and 45 nm node, parameters can be found to fulfill the ITRS requirements [1] for keff. Lower k-values of the functional layers are needed, if the thickness has to be increased for processing reasons. For example k=5.5 and thickness of 15 nm yield a keff of about 2.5 for the 45 nm node. Ultimate effective k-values of 2.0 and below could be achieved for lower k-value or thickness of the functional films.