Application of stress reversal of metal hardmask for 20nm and beyond

TiN metal hard mask (MHM) scheme has become necessary in Cu interconnects when ultra-low k (ULK) materials is introduced. As scale down, the biggest challenge of MHM scheme is how to control the residual stress of TiN layer as the poor mechanical strength of ULK. The deformation (even collapse) of trench structure is found because of the high residual compressive stress in TiN film and Cu voids occur due to the further shrinkage of the feature sizes. In order to solve this issue, a TiN layer with ultra-low compressive stress or even tensile stress is necessary in 20nm and beyond. In this paper, a tensile stress TiN is applied to improve the trench deformation. The results show that MHM scheme using TiN film with tensile stress is a promising technology for 20nm node Cu interconnects and beyond.