Microstructure Control in Semiconductor Metallization

The microstructure of semiconductor metallization is becoming increasingly important as linewidths decrease below 0.5 um. At these dimensions, reliability and performance are greatly influenced by specific microstructural features, rather than only the average material properties. In this paper, we address the prospects for controlling the microstructure of thin film interconnection metals as linewidths are predicted to decrese below 0.1 um by the year 2010. First, we evaluate the sources of energy available to drive microstructure changes in thin films, both during and after deposition. The internal energy sources considered are grain boundaries, interfaces, surfaces, strain, solidification, crystallization, solute precipitation and phase transformations, with energy densities ranging from less than 1meV/atom to greater than 0.1 eV/atom. The external energy sources considered are particle bombardment during deposition, mechanical deformation and radiation damage, which may deliver energies greater than 100 eV/atom. Second, we review examples of microstructure changes in terms of these energy sources. These examples include the dependence of Al-Cu and Ti fiber texture on the roughness of SiO2, orientation change and abnormal Cu grain growth coupled to the precipitation of Co in Cu-Co alloys, and in-plane orientation selection during phase transformation of TiSi2 in very narrow lines. A substantial degree of microstructure control is also achieved in films deposited..