Exploring 3D architectures and superconducting interconnects using highly conformal ALD and CVD: a BEOL-compatible process for superconducting MgB₂

The ability to fabricate 3D architectures and superconducting interconnects can be an enabling technology towards the scale up of quantum computing architectures. One of the key challenges is that physical vapor deposition methods, such as evaporation or sputtering, struggle to coat or infiltrate high aspect ratio structures, being traditionally limited to aspect ratios of 10:1 or lower. In this work we explore how to take advantage of the high conformality of ALD and some CVD processes to overcome this limitation. In particular, we have developed a BEOL-compatible, diborane-free process that is capable of growing superconducting magnesium diboride at low temperatures. This process has allowed us to demonstrate critical temperatures exceeding 20K in films that are just a few nm thick, and the formation of stable interfaces with oxide materials. Together with existing ALD processes for superconducting nitrides, we believe that this process can help us explore new device configuration, including the design of architectures with vertical junctions, or the development of superconducting interposers for advanced packaging applications.