Copper (Cu) interconnects used in modern nano-electronic devices scale in accordance with the Moore’s law. By the year 2020, interconnect dimensions are expected to shrink well below 10 nm, necessitating the development of advanced electrochemical processes for deposition and fabrication of nano-scale Cu films. One such electrochemical process, called ‘electroless’ deposition, involves the use of organic reducing agents in the electrolyte, which reduce complexed Cu-ions to metallic Cu. By design, electroless deposition provides excellent nucleation when depositing Cu onto foreign substrates and favors uniform macro-scale deposit distribution – attributes that make electroless processes attractive for advanced interconnect metallization applications.
In this talk, we will outline a novel electroless Cu deposition process for fabricating smooth and continuous sub-5nm Cu films on a resistive ruthenium (Ru) substrate. A critical element of our novel electroless process is the use of ppm-levels of electrolyte additives, which enhance the nucleation density during electroless deposition. Mechanistic aspects of how these additives function will be discussed. A particularly important challenge in understanding nucleation and growth of nano-scale films is the need for reliable in situ metrology. In this context, we will discuss a novel electrochemical method, utilizing underpotential deposition, for characterizing the surface coverage and roughness evolution during nano-scale electroless film growth. Insights into additive adsorption during electroless deposition and its effects on nucleation and film coalescence obtained using the aforementioned technique will be discussed.