Wafer Level Supercritical Carbon Dioxide-Based Metal Deposition for Microelectronic Applications

This research project involves the application, development, and commercial scale up of a process for the deposition of copper and copper barrier materials such as ruthenium, titanium, and other metals. This process could replace copper electroplating currently used to fill deep trenches and thin-film deposition in microelectronic circuit manufacturing. In addition, physical vapor deposition and electroless deposition of barrier materials also could be replaced. The electroplating process generates large quantities of aqueous wastes with copper ions and other dangerous chemicals that must be treated in place. MiCell Technologies, Inc.’s proposed process uses liquid or supercritical carbon dioxide (CO2) solvent to transport a metal precursor to a semiconducting wafer substrate. In addition to being environmentally benign, this process provides additional control of the metal deposition process to create superior films and electrical interconnects. This research project is part of an overall strategy to replace aqueous and organic solvents in microelectronics fabrication. The wafer to be coated will be immersed in supercritical CO2 solvent containing the precursor. The wafer is heated independently of the chamber and a reactant is added to initiate a reaction with a metal precursor leaving behind a metal film on the wafer substrate surface. Because of the low surface tension and viscosity of the CO2 phase, the precursor will penetrate uniformly into the narrow gaps on the surface of the patterned substrate. After the conversion of the metal precursor, a solid metallic layer remains on the surface that forms the desired interconnect, thin layer structure, or barrier layer. Because of the never-ending demand for faster processor speeds and enhanced storage capacities, smaller and more sophisticated structures are required in modern semiconductor products. As dimensions shrink, copper interconnects and metallic barrier and seed layers will be scrutinized like never before in efforts to achieve maximum yields. New processes and materials will be adopted in the coming years to meet the challenges of evolving semiconductor products. As an environmentally benign and technically superior process, metal deposition from supercritical CO2 will have a preferred position in the marketplace.