Integration of Cu and low-k dielectrics: effect of hard mask and dry etch on electrical performance of damascene structures

In this work we discuss the importance of selecting the hard mask material and choosing the optimum dry etch and post-CMP clean processes on the integration of Cu and organic low-k dielectrics. The hard mask material plays an important role in the interline capacitance and in the effective dielectric constant of the interconnects. One generation of effective k can be gained simply by replacing the hard mask material by one with a lower dielectric constant, instead of moving to a more advanced low-k material. Interline leakage is not affected by the hard mask material and low values (approx =10 exp -9 A/cm exp 2 ) are obtained at electric fields of 1 MV/cm for structures with spacing down to 0.2 mu m. A non-optimized dry etch process for trench definition can result in undercutting, which affects the Cu filling of the trenches. From our results it is clear that the process conditions (lithography, etch, CMP) affect the geometry of the structures, which has a big impact on the effective dielectric constant of the interconnects.