Thermal furnace and Ultraviolet assisted curing impact on SiOCH spin-on ultra low dielectric constant materials

In recent years, the continuous progression of ultra-large scale integration has driven the emergence of technological solutions. In particular, major challenges have been faced for the fabrication of interconnect structures, where ultra low dielectric constants are required to decrease the parasitic capacitances between metal lines. Porous material, obtained using the porogen approach, is the main candidate investigated. The curing process is critical for achieving a good control of final film structure. The integration of such material requires a good chemical and mechanical stability, particularly to maintain the structure integrity during the stressing steps: chemical mechanical polishing and packaging. In this work, Ultraviolet assisted thermal cure (or UV curing) is investigated as an alternative solution to the conventional thermal curing. Chemical and physical analyses reveal that the best porogen removal efficiency and the enhancement of matrix crosslinking are achieved when the material is UV cured. This crosslinking improvement (as indicated by higher Si–O–Si bond density in the fourier transformed infra-red spectra) can be correlated to better mechanical properties. Significantly better electrical properties (dielectric constant, leakage current and breakdown voltage) are obtained with better integrity (no moisture uptake after 1 week storage in humid atmosphere 85 °C/85% relative humidity) when the dielectric is optimally cured. Porosity evaluation reveals similar results between both curing processes with slightly larger pore size in the case of the UV cured film. Finally, a basic model is described to illustrate how the UV assisted thermal cure may improve the crosslinking in comparison to the thermal curing. Selective UV action is proposed to explain the curing process kinetics.