Dual hard mask process for low-k porous organosilica dielectric in copper dual damascene interconnect fabrication

Using a low-k porous organosilisesqueoxane film, ALCAP ^TM-S with k=2.1, dual hard mask (DHM) process is proposed for Cu dual damascene interconnect (DDI) formation. The porous organosilica film has very high etching rate relative to those of the hard mask (HM) and/or etch-stop materials. SiO ₂/SiC is one of the best combinations for the DHM, in which the lower hard mask of SiC remained after metal CMP and protects the porous film from the via-etching damage in misalignnent region between the via-hole and the buried Cu-line. Applying in-situ resist-ashing with N ₂/H ₂ gas, 0.4 μm-pitched dual damascene structure is successfully fabricated. Increment of the dielectric constant is suppressed within 5% (k=2.2) after the Cu-interconnect fabrication, confirming that the DHM low-damage process is applicable for the Cu DDI fabrication in ultra low-k, porous organosilica systems.