Achieving ultra low k dielectric constant for nanoelectronics interconnect systems

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 k _eff 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 fulfil the ITRS requirements for k_eff. 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 k_eff 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