Electrical and mechanical properties of Au-Si bonds for 3D interconnect applications

Driven by high-density and high-reliability demands on three-dimensional (3D) interconnections, electrical and mechanical properties of interconnection structures have been paid more attention. Aiming at the novel enable-3D interconnections realized by Au-Si wafer bonding, this study demonstrates the design, fabrication and test results of testing structures for dimension-define parameters of Au-Si bonds. In order to measure closely-realistic ohmic contact resistances of Au-Si bonds after wafer bonding processes implemented under certain bonding pressures and temperatures, the convex Si structures formed by the local oxidation of silicon process have been designed. Therefrom the specific contact resistance values of Au-Si bonds have been measured as 3.9-8.1 x 10(-10)omega m(2) for different contact radii (3-20 mu m), which indicates the low-resistance potentiality for Au-Si bonds applied on 3D interconnections. On the other hand, two findings on bonding strengths are summarized from finite element simulations and tensile experiments: (a) Au-Si bonding strengths of circular bonding patterns (35-75 MPa) are superior to the ones of square bonding patterns (18-30 MPa) due to the stress concentration phenomenon on four corners of square bonding patterns; (b) there is an inverse relationship between bonding strengths and bonding areas owing to uneven stress distributions in bonding structures. Overall, this study provides a basic optimization design strategy at electrical and mechanical levels for 3D interconnections actualized by Au-Si bonding. Incidentally, these introduced analysis methods are also feasible for homologous Si-based eutectic bonding techniques to extend the forms of 3D interconnections.