Investigate an Alternative to Aqua Regia for Backside Metal Contamination Removal

Rigorous management of metallic contamination is crucial in microelectronics to ensure device performance. For advanced laboratories seeking to work on a wide variety of diverse projects, one challenge is, for example, to make 3D integration technology using noble metals coexist with more sensitive technologies, such as photonics. To prevent metallic cross contamination between tools, recurrent backside and bevel cleaning is mandatory throughout the process flow. The aim of the paper is to find an alternative to traditional aqua regia mixture, which is known to dissolve noble metals. For this purpose, two promising solutions for metallic contamination removal are TechniClean IK73-based and TechniClean NPS78-based solutions. The TechniClean NPS78-based solution was almost as effective as aqua regia on noble metals but introduced bromide contamination. The TechniClean IK73-based solution showed varying effectiveness depending on the metal and substrate. Silicon consumption was a key parameter for contamination removal on silicon substrates. On oxide substrates, the addition of hydrogen peroxide enhanced metal removal efficiency. Stability tests over one week and metallic loading tests showed good performance, but issues with evaporation needed to be addressed. Transferring the process to a single wafer tool is expected to optimize performance and address eco-design requirements. Further evaluation will assess the lifespan of equipment and the potential for reclaimable chemistry.