Low temperature direct Cu bonding assisted by residual stress

Cu-to-Cu direct bonding is one of the key technologies for 3D (three-dimensional) chip stacking. This research proposes a new concept to enhance Cu-Cu direct bonding through the control of residual stresses on bonding surface. Compressive residual stress induced by near-infrared radiation (NIR) enhances the diffusion of copper atoms and thus direct bonding. Subjected to thermal compression bonding at 250°C for 5 min under 10 MPa in N2, joint strength of 28.9MPa between two Cu films exposed with NIR for 10 sec can be obtained.