Process Optimization and Integration of HFO2 and HF-Silicates

Abstract

ABSTRACTWe have established in-line characterization techniques for analyzing the bulk and interface-charge properties of dielectric films, for process optimization. Surface charge analysis (SCA) is used to determine the densities of interface states, fixed charge, and near-interface traps in ultra-thin dielectrics, and is useful for tracking the influence of post-deposition processing on interface-charge properties. Spectroscopic ellipsometry (SE) is used to obtain the absorption spectra in the conduction band-tail region. The intensity of an extra absorption peak inside the bandgap of HfO2 is clearly correlated with leakage current density and near-interface trap density. Based on the observed process dependencies, defects within the HfO2 films are likely to be oxygen vacancies. The relative scalability of HfO2 and Hf-silicate films of various compositions is examined using a figure of merit based on the direct-tunneling leakage current model. Pure HfO2 is expected to be more scalable than Hf-silicates. However, it is typically accompanied by an interfacial layer which significantly increases the equivalent oxide thickness (EOT). A 20% Hf silicate with relative permittivity of 11 or higher can be more scalable than HfO2 with an interfacial layer. Alternatively, an ultra-thin interfacial Si3N4 diffusion barrier can be used with HfO2, to allow for more aggressive EOT scaling. The dependencies of interface-charge properties and surface roughness on the nitride barrier formation process are presented.