S-parameters-based high speed signal characterization of Al interconnect on low-k hydrogen silsesquioxane-Si substrate

In this study, hydrogen silsesquioxane (HSQ) thin films prepared under various conditions are employed as the intermetal dielectric and the high frequency characteristics of Al-HSQ system are investigated and compared with those of Al-SiO2 system. The S-parameters of the Al interconnect are measured for insertion loss and crosstalk noise. The interconnect transmission parameters are extracted from the S-parameters. A figure of merit (FOM) is employed to evaluate the characteristics of the Al-HSQ system at high frequencies (100 MHz-20 GHz). It is found that Al interconnect with HSQ films annealed at 400 °C has an insertion loss of 1.64 dB/mm, a coupling of −13.3 2 dB at 20 GHz, and a propagation delay of 0.121 ps/μm, while those of the PECVD SiO2 films are 2.01 dB/mm (insertion loss), −13.40 dB (coupling), and 0.149 ps/μm (propagation delay). The Al-400 °C-annealed-HSQ system has better performance than the Al-SiO2 system does from 100 MHz to 20 GHz. However, specimens with 350 °C-annealed HSQ films or plasma-treated HSQ films exhibit larger insertion losses and higher crosstalk noises than those with PECVD SiO2 films do. Both annealing temperature and O2 plasma treatment of the HSQ films affect the high frequency characteristics of the Al-HSQ system.