Development of a permittivity extraction method for ultra low k dielectrics integrated in advanced interconnects

An extraction method to determine the permittivity of ultra low k (ULK) dielectrics on real integrated structures is presented. It is a two-step method based on a comparison between measured and simulated capacitance. A best-estimate value of the kULK value is first extracted with optimization software coupled to capacitance extraction software. Secondly, uncertainties on material and process parameters are considered to determine an error margin on the best-estimate extracted k value. The uncertainty on the best-estimate value is approximated by a function of the uncertainties on material and process variables. This function is calculated using a multi-linear approximation model and a numerical design of experiments. The same method is applied for the extraction of a ULK material k value (kULK) value and an effective k value (keff) but with two different simulation structures. In the simulation structure used for keff extraction, an equivalent dielectric layer including the ULK layer, the etch-stop and capping layers is used. This method was applied to metal 1 single damascene structures. First results of extraction are presented for two different ULK dielectrics. With the estimated uncertainty used for the parameters in this work, the uncertainties obtained for the best-estimate value of kULK and keffective are significant. Due to the linearity of the model, the method is still applicable with different values for parameters uncertainty. An analysis work will be realized to improve the parameters uncertainty estimation. Future work will also include extraction of ULK permittivity for more complex structures like double damascene structures.