Stress gradients observed in Cu thin films induced by capping layers

Glancing-incidence x-ray diffraction (GIXRD) has been applied to the investigation of depth-dependent stress distributions within electroplated Cu films due to overlying capping layers. Cu films, 0.65 μm thick, plated on conventional barrier and seed layers received a chemical vapor deposited (CVD) SiCxNyHz cap, an electrolessly deposited CoWP layer, or a CoWP layer followed by a SiCxNyHz cap. GIXRD and conventional x-ray diffraction measurements revealed that strain gradients were created in Cu films possessing a SiCxN yHz cap, where a greater in-plane tensile stress of approximately 180 MPa was generated near the film/cap interface as a result of constraint imposed by the SiCxNyHz layer during cooling from the cap deposition temperature. Although Cu films possessing a CoWP cap without a SiCxNyHz layer did not exhibit depth-dependent stress distributions, subsequent annealing introduced stress gradients and increased the bulk Cu stress. However, a thermal excursion to liquid-nitrogen temperatures significantly reduced tensile stresses in the Cu films. © 2010 Materials Research Society.