Thermal stability and gap-fill properties of spin-on MSQ low-k dielectrics

Looking onto integration of low-k materials within FEOL used processing temperatures in this field are much higher than within BEOL. In addition partly high aspect ratio features have to be filled without defects, e.g. within usage of spin-on low-k materials for shallow trench isolation. We evaluated two MSQ-based spin-on dielectrics, a porous ultralow-k material and a dense spin-on glass regarding their thermal stability and gap-fill behaviour. The films were annealed from standard curing temperatures up to temperatures of 850 °C and 900 °C, film thickness and refractive index were measured by spectral ellipsometry, electrical film properties were evaluated by a mercury probe measurement and changes within chemistry are studied by FTIR. Both low-k materials are thermally stable up to temperatures of 650–700 °C. Above this range the film thickness is rapidly decreasing, refractive index and corresponding to that the k-value are strongly increasing, as does the leakage current density. FTIR spectra show a shift within Si–O–Si backbone and Si–CH3 and CH3 bonds are vanishing, while OH groups are adsorbed, additionally leading to higher k-value and leakage currents. Both materials show very good gap-fill properties, filling features with aspect ratios up to 5 or 10 and Aluminium covered structures without any visible defects.