Electrical stability and reliability of ultralow dielectric constant porous carbon-doped oxide film for copper interconnect

Abstract

Nanoporous carbon-doped oxide (CDO) is a promising low dielectric constant (low-k) intermetal dielectric (IMD) for Cu interconnect. The electrical stability and reliability of CDO strongly depend on the contacted metal. An electrical instability model considering metal ion diffusion, dielectric polarization, and carrier injection is proposed for CDO under electrical stress. Both Al and Cu are not suitable for contact with CDO because they can be driven easily into CDO. Fortunately, TaN shows no mobile ion issues when in contact with CDO. The electron transport mechanism is identified to be Schottky emission at low electric field and low temperature. As metal ions are injected into CDO film, the electron transport mechanism changes to Frenkel-Pool emission at high temperature and high electric field. The injection of metal ions into CDO also degrades the time-dependent dielectric breakdown (TDDB) lifetime of CDO. Fortunately, the commonly used diffusion barrier TaN is an excellent contact metal with CDO. The 1-year-long TDDB lifetime allows an electric field stronger than 2 MV/cm, and the TDDB lifetime at 0.5 MV/cm becomes longer than 10 years by several orders of magnitude. It is concluded that the nanoporous CDO is a very promising IMD for next-generation interconnect systems. (c) 2005 The Electrochemical Society.