Precleans challenges on middle-of-the-line contacts for 14nm technologies and beyond

In-situ dry cleans of silicon-based surfaces preceding the metallization process step have a crucial impact on contact resistance, yield and reliability of middle-of-the-line (MOL) local interconnects. Existing precleaning techniques meet numerous challenges predominantly originated from reduced device geometries such as critical dimensions enlargements, epitaxial junctions gouging and insufficient native oxide removal. Reactive chemical cleans employing remote plasma assisted with NF3/NH3 gas mixtures designated as SiCoNi™ include complex etchant-surface interactions. This report discusses junction-to-metal interfacial aspects of physical and chemical precleans applied to MOL contacts. The fundamental mechanisms that govern clean efficiency of MOL contacts are analyzed in order to insure the manufacturability of defect-free local interconnects.