Use of a capacitance voltage technique to study copper drift diffusion in (porous) inorganic low-k materials

摘要

Cu~+ drift diffusion in two inorganic low-k materials is evaluated. The diffusion is investigated by measuring shifts in the flatband voltage of capacitance/voltage measurements on Cu gate capacitors after bias temperature stressing. The Cu~+ drift rate in SiO_xC_y (2.7≤k≤3.1) is considerably lower than in PECVD oxide. This electrical method is not suited for a porous silicon resin (k ≈ 2.0) because of the occurrence of instabilities in the metal/dielectric. A modification of the measurement technique is required. The modification consists of measuring the Cu~+ ions, which have been diffused through the porous dielectric in an underlying thermal oxide layer. The Cu~+ drift mobility in the porous dielectric as measured by this method appears to be lower than in thermal oxide.