Demonstration of Superconducting Interconnects on the Silicon Interconnect Fabric Using Thermocompression Bonding

In this paper, the silicon interconnect fabric (Si-IF) technology is extended to superconducting electronics using niobium (Nb) as the superconducting interconnect (Superconducting-IF). It has advantages of solderless metal- metal interconnects, fine pitch integration (≤ 10 μm), no complex packaging, an inter-dielet spacing of <; 100 μm, high bandwidth, low latency, low power generation and low power dissipation. In this platform, superconductor, Nb, is used as the interconnect material and a low-temperature Au-Au thermocompression bonding at 140°C that retains the transition temperature is established. Au-Au bonding was first studied and optimized through shear strength tests using a blanket structure. The average shear force obtained was >100 N over 2×2 mm
²
dies. The optimized parameters are: a 3-min Ar plasma surface pre-bonding clean, a bonding temperature of 140°C, at a bonding pressure of 35 MPa for a duration of 1.5 s followed by a post-bond annealing duration of 2 min at 140°C. A Kelvin test structure was fabricated to measure the superconductivity of Nb before and after each process. Under all processing conditions, the transition temperature of Nb remained at 9 K The resistance of Nb interconnects with Au thin-film bonding sites approached zero below the transition temperature of 9 K.