Interference Lithography‐Based Fabrication of 3D Metallic Mesostructures on Reflective Substrates using Electrodeposition‐Compatible Anti‐Reflection Coatings for Power Electronics Cooling

Abstract A nanostructured copper oxide (nCO) coating which can be electrochemically reduced to copper metal is demonstrated as an anti‐reflection coating, enabling interference lithography of three‐dimensionally structured templates on a surface compatible with subsequent electrodeposition steps. The nCO presents a black needle‐like structure which effectively absorbs the incident radiation during interference lithography. Specular and diffused reflectivity measurements confirm nCO has near‐zero reflectivity from at least UV (350 nm) to near IR (700 nm) wavelengths. A particularly important aspect of the nCO is its ability to be reduced to copper metal, enabling electrodeposition inside porous templates fabricated on the nCO. It is demonstrated electrodeposition of copper within 3D templates defined by interference lithography and proximity field nano‐patterning processes, forming mesostructured metals which enhance two‐phase cooling. The resultant 5 µm thick structures exhibited up to 3 times the critical heat flux and 2 times heat transfer coefficient of bare silicon. The structures are optimized via computational tools including Finite Difference Time Domain (FDTD) and COMSOL Multiphysics. The use of the approach demonstrated here can potentially find application in many areas given the broad importance of mesostructured metals for energy, biomedical, and mechanical applications.