DESIGN ISSUES IN IONIZED METAL PHYSICAL VAPOR-DEPOSITION OF COPPER

The filling of deep vias and trenches with metal for interconnect laye rs in microelectronic devices requires anisotropic deposition techniqu es to avoid formation of voids. Ionized metal physical vapor depositio n (IMPVD) is a process which is being developed to address this need. In IMPVD, a magnetron sputter deposition source is augmented with a se condary plasma source with the goal of ionizing a large fraction of th e metal atoms. Application of a bias to the substrate results in an an isotropic flux of metal ions for deposition, The ion flux also contrib utes to ''sputter back'' of metal deposits on the lip of the via which could lead to void formation, In this article, we describe and presen t results from a two-dimensional plasma model for IMPVD using a de mag netron and an inductively coupled auxiliary ionization source. The sca ling of copper IMPVD is discussed as a function of buffer gas pressure , sputter source, and source geometry. We show that the deposition rat e of metal on the substrate will be reduced as pressure increases due to the increase in diffusive losses. We also show that the sputtering of the auxiliary coils can be a significant issue in IMPVD systems, wh ich must be addressed in tool design, (C) 1998 American Institute of P hysics.