Overview of Ruthenium Thin Films Annealed by Microsecond Scanning UV Pulsed Laser: Structural, Electrical, and Failure Modes Analysis

Abstract

Ruthenium (Ru) has been identified as a durable and relevant substitute to copper (Cu) to answer the access resistance lowering of the back-end-of-line (BEOL) metal levels, which is a high-priority concern for future devices. Herein, the nonequilibrium and local properties of pulsed scanning laser annealing (SLA) technique are used to enhance the structural and electrical properties of thin polycrystalline Ru layers (<30 nm). For the best annealing conditions, transmission electron microscopy observations show a substantial grain size enlargement, with large grains (≈80 nm) occupying the whole layer height. It goes with a 53% resistivity reduction, measured by 4-point probe, confirming the strong grain boundary scattering reduction. A Mayadas–Shatzkes model incorporating temperature-dependent resistivity measurements allows the extraction of promising reflectivity and specularity coefficients of around 0.58 and 0.98, respectively. Beyond the best conditions, failure modes for devices integration are observed, such as surface wrinkling and local buckling. Given the studied system, a semiquantitative analysis of these phenomena is given and simulations based on the finite element method are used to find further optimal annealing conditions. This study confirms the potential of Ru as a promising BEOL material, but also SLA as a convincing technique for future 3D architectures.