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 degrees 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 chance of Ti lattice parameter Cu have been observed. Ar 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 degrees 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 degrees 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 degrees 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.