Impact of ultra low k dielectrics on RF-performance of inductors

Low k and ultra low k dielectrics will be integrated in the lower metal levels of sub-100nm technology nodes in order to reduce RC delay. Several product applications require on chip inductors of high quality, which are typically integrated in the top levels of such multilevel metal schemes. This paper provides experimental and simulation results for the impact of SiO2 substitution by low-k dielectrics on the quality factor Q and the resonant frequency f(res) of inductors ranging from 1 to 20 nH. Substitution of SiO2 by low k in one or more levels has a beneficial impact on Q and f(res), which depends upon the k value, dielectric thickness, low k location, but also upon the inductor design and inductivity. In good agreement of experimental and simulation results, maximum improvements of 25% for f(res) and 16% for Q are found for the investigated inductor designs, if complete substitution of SiO2 by k = 2.2 dielectric in the lower levels is assumed.