Evaluation of adhesion energy and its correlation to apparent strength for Cu/SiN interface in copper damascene interconnect structures

Local apparent strength of interface between copper and cap layer on top was diverse depending on the crystal orientation underneath. For a comprehension of this diversity, physical adhesion energy to separate the interface was evaluated. It essentially does not include mechanical energy dissipating in plastic deformation in the process of crack extension. Sub-micron scale torsion test for elastic-plastic deformation properties and fracture tests on a number of different crystal orientations revealed that difference in adhesion energy is much smaller than difference in plastic dissipation energy. It is highly likely that small difference in the former is intensified through the latter, leading to a huge scatter in strength of LSI interconnect structures.