Electrical conductivity of high aspect ratio trenches in chemical-vapor deposition W technology

Abstract

This article discusses the resistivity scaling challenges associated with the use of high aspect ratio trenches as W interconnects for the sub-130-nm semiconductor technology node. In this work, chemical-vapor deposition of W is employed to manufacture conductive trenches in a deposition sequence that includes a TiN barrier, a nucleation W, and a bulk W film. Composition, microstructure, resistivity, grain size, and surface roughness for these films are determined in the low thickness range. The results are used to examine the contribution of the electron-surface scattering and grain-boundary scattering to the overall increase in the electrical resistivity observed at film thickness comparable to the electron mean free path. Calculated and measured values for the film resistivity are matched by using a variable coefficient of elastic electron scattering at the grain boundaries. In first approximation, grain-boundary electron scattering is found to be the dominant mechanism and is almost entirely responsible for the resistivity increase in the thickness range studied. By using resistivity data obtained for each film and Kirchhoff’s rule for laminate structures, a simple physical model is used to predict the variation of the trench resistance as a function of geometrical factors such as film thickness and core (seam) size. The agreement between the calculated and measured trench resistances is surprisingly good in view of the several simplification assumptions that are made and that no fitting parameters are used. The proposed model predicts reasonably well the sensitivity of the trench resistance with respect to the TiN film thickness. However, the impact of the nucleation W layer is overestimated, which suggests possible unaccounted interactions, related to structural or morphological changes in the bulk W. It is concluded that the trench conductivity is already significantly size limited for critical dimensions in the sub-130-nm range. The control of the film bulk resistivity and grain-boundary engineering of the conducting materials is therefore identified as the most important pathway for achieving desired electrical properties in conducting trenches filled by standard chemical-vapor deposition W technology.