Thin film interaction between low-k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer

The interaction between low-k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer has been studied using four-point-probe sheet resistance measurement, X-ray diffraction, conventional Rutherford backscattering spectrometry (RBS), nuclear resonance analysis (NRA), elastic recoil detection (ERD), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). The conventional intermetal dielectrics SiO₂ and plasma-enhanced tetraethylorthosilicate (PETEOS) have been studied also for the purpose of comparison with HSQ. In the low temperature regime (300–550°C), a considerable amount of oxygen atoms, from various sources, diffuses into Ti film to form a Ti(O) solid solution, raising the resistivity of Ti significantly and causing the expansion of the Ti lattice. A good correlation between the oxygen composition in the Ti film, the sheet resistance variation of Ti and the change of Ti lattice parameter C₀ have been observed. At the same temperature, there are more oxygen atoms incorporated into the Ti film in Ti/HSQ than those for Ti/PETEOS, suggesting that additional HSQ-related oxygen sources, such as the moisture uptake and the conversion reaction of HSQ, may be attributed to this. In the high temperature regime (550–700°C), HSQ reacts with Ti to form a final TiO/Ti₅Si₃/HSQ stack structure. It is assumed that a few competing reactions occur in this regime. At 550–650°C, HSQ reacts directly with Ti; in the meantime, part of HSQ undergoes conversion reactions, with the reaction products SiO₂ and SiH₄ reacting with Ti to form Ti silicide. At 650–700°C, HSQ is almost completely converted into SiO₂, so the dominant mechanism is Ti reaction with SiO₂. Before HSQ is completely turned into SiO₂, the Ti/HSQ system is more reactive than both Ti/PETEOS and Ti/SiO₂. The initiating temperature for the Ti/HSQ reaction exhibits no obvious Ti thickness dependence.