(354a) Bipolar Applied Field Experiments to Characterize Dielectric Relaxation and Describe Charge Transport in Low-k Materials

Time dependent dielectric failure (TDDB) continues to be an important part of interconnect design as industry pursues integration of sub-45 nm process-technology nodes. The TDDB literature has provided key information about the role played by diffusing species such as electrons, holes, ions and neutral impurity atoms. However, no mechanism has been shown to describe how these species interact and affect dielectric failure. Charge relaxation in low-k dielectrics was studied using bipolar field experiments² coupled with a charge transport model.  The goal is to tie changes in dielectric relaxation behavior to the injection and transport of charged species such as electrons, ions and traps to dielectric breakdown. We show that current relaxation upon inversion of the applied field can be described with classical dielectric relaxation models such the stretched exponential function, providing insight into charge transport in disordered materials. The kinetics of charge trapping events have been found to be consistent with a time-dependent reaction rate constant of the form t^β-1, 0<β<1. Such dynamics have previously been observed in studies of charge trapping reactions in amorphous solids by Hamill and Funabashi. We explain the relaxation process in charge trapping events by developing a nonlinear charge transport model. Experiments for leakage relaxation at various temperatures and field strengths have been correlated to predictions from the model. These studies promise to help on designing robust low-κ and ultra-low-κ materials by providing insight into the dynamics of charge transport and charge relaxation during bias temperature stress.

1.      Hamill, W. H. and Funabashi, K. "Kinetics of electron trapping reactions in amorphous solids; a non-Gaussian diffusion model," Phys. Rev. B,vol. 16, Dec. 1977.

2.      J. Borja, J. L. Plawsky, T-M. Lu, W.N. Gill "Impact of frequency from bipolar applied field on dielectric breakdown for low-k materials," under review in IEEE Transactions on Electron Devices.