Mechanical properties of high porosity low-k dielectric nano-films determined by Brillouin light scattering

Integrating nanometre sized pores into hybrid organic-inorganic interconnect layers is one of the key approaches being undertaken by the semiconductor industry to sustain the continued scale down of micro-electronic devices. While increasing porosity of the layers achieves the desirable lowering of the dielectric constant (k), it also has the potential to reduce mechanical and thermal stability and degrade device functionality. We report on Brillouin light scattering to measure the independent elastic constants, and thus the mechanical properties, of ultrathin dielectric films with porosity levels up to 45%, the highest in the industry. Longitudinal and transverse acoustic standing mode type excitations were observed from sub 200nm thick low-k thin films, and their frequency dispersion and associated light scattering intensities were utilized to determine Poisson’s ratio (ν)and Young’s modulus (E). In comparison with SiO2 and non-porous low-k materials, significant modifications were found in ν and E of these highly porous carbon-doped SiO2 (Si‐O‐C‐H) and amorphous carbon (a-C:H) low-k interlayer dielectrics.