Communication—Effect of Fluorine on Formation of Hillock Defect in Copper Metallization and Methods to Remove Them

We have reduced the occurrence of copper hillock defects in dynamic random access memory devices by 94% through silane and nitrogen purge, allowing fluorine adsorbed on surfaces of chambers from in situ NF 3 plasma cleaning to react and be removed as gaseous SiF x . We have discovered these defects were more pronounced at grain boundaries, where concentration of fluorine built up due to ion migration causing oxidation of metallic copper forming CuF x . COMSOL solid mechanics simulation confirmed that hillock formation is due to larger thermal expansion coefficient and molecular volume of CuF x causing inelastic deformation to relieve thermal stress.