Thermal stability of trimethylsilylated mesoporous silica thin films as the ultralow-k dielectric for copper interconnects

Abstract

Surfactant templated mesoporous silica thin films were prepared as the intermetal dielectric for ultralarge scaled integrated circuit application, and the thermal and chemical stability of the Cu/nitrided Ta/mesoporous silica film stack on the Si wafer was studied. Trimethylsilylation of the mesoporous silica thin film by hexamethyldisilazane vapor treatment significantly improves hydrophobicity of the mesoporous dielectric, and a dielectric constant (k) smaller than 2 can be obtained for the thin film. According to Fourier transform infrared spectroscopy and thermal desorption spectroscopy, decomposition of trimethylsilyl groups on the pore surface becomes significant at temperatures larger than 400 degrees C. However, when the metallized film stack was annealed at temperatures higher than 400 degrees C, the film stack shows little delamination between layers and still retains smooth interfaces according to Auger electron spectroscopy and transmission electron microscopy analyses. Ta2C nanoparticles were found to exist at the Ta(N)/mesoporous silica interface of the film stack annealed at 600 degrees C. Bias-temperature stress test of the metallized film stack shows little Cu diffusion into the mesoporous dielectric layer. (c) 2005 American Vacuum Society.