Effectiveness of Ti, TiN, Ta, TaN, and W2N as barriers for the integration of low- k dielectric hydrogen silsesquioxane

The interactions between low-k (dielectric constant) material hydrogen silsesquioxane (HSQ) and barrier layers, Ti, Ta, physical-vapor deposited (PVD), and chemical-vapor deposited (CVD) TiN, PVD TaN, and CVD W2N, have been investigated by using sheet-resistance measurement, x-ray diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, elastic resonance scattering, and forward recoil spectrometry. The conventionally used dielectric PETEOS [plasma-enhanced chemical vapor deposition tetraethylorthosilicate (TEOS)] was also studied as a control. The results show that none of these barriers except Ti can react with HSQ and PETEOS at elevated temperatures. However, significant outdiffusion of hydrogen due to the degradation of the HSQ films upon annealing exists for all barrier/HSQ structures, and exhibits a strong barrier dependence. Metal barriers Ti and Ta, and CVD TiN can retard the H outdiffusion, whereas PVD TaN and PVD TiN induce the H outdiffusion from the HSQ films. The microstructural and structural considerations and a proposed “nitride effect” mechanism can give some reasonable interpretations to these observations. Upon annealing, the structural and/or compositional changes of these barrier films give rise to corresponding sheet resistance variations. The phase transformation of the Ta film on HSQ is completely inhibited because of the possible role of diffusing H atoms, as compared to the phase transformation occurring in the Ta film on PETEOS.