SBIR-STTR Award

MiCell Technologies, Inc., proposes a new process for the deposition of metallic thin films of copper, ruthenium, titanium, and other metals used as barrier layers, seed layers, and interconnects. This process would replace the current electroplating approach used in filling deep trenches and forming thin films in microelectronic circuit manufacturing. The electroplating process generates large quantities of aqueous wastes with copper ions and other dangerous chemicals that must be treated in place. The process being proposed utilizes liquid or supercritical carbon dioxide as the solvent. In addition to being environmentally benign, this process also will provide additional control of the metal deposition processes to create high-quality films and electrical interconnects. This project is part of an overall strategy to replace all aqueous and organic solvents in microelectronics fabrication. The proposed fluid displacement deposition process utilizes a two-step approach to the formation of the deposited metallic layers. In the first step, organometallic precursors will be dissolved in either liquid or supercritical carbon dioxide. The wafer to be coated will be immersed in either the liquid or supercritical solvent. This solution will be displaced either with carbon dioxide itself or by a second fluid, such as helium, in the supercritical state. This displacement step will cause the formation of a thin film that will result in the deposition of the organometallic precursor on the wafer surface. Because of the low surface tension and viscosity of the carbon dioxide phase, the precursor will penetrate uniformly into the narrow gaps on the surface of the circuit. After this film displacement step, the system can be heated and a reducing agent, such as hydrogen, can be introduced to remove the organic ligands bound to the metal atoms. After the reduction step, a solid metallic layer will remain on the surface, which will form the desired interconnect or thin layer structures. Phase I will determine the more important operating variables in both the liquid and supercritical carbon dioxide surface deposition processes. Phase II will involve the design of a metallization tool that will meet the operating requirements of industrial microelectronics fabrication. Because of the demand for faster, more sophisticated structures in modern electronic products, copper interconnects and metallic barrier and seed layers will play an increasing role in device fabrication. This environmentally benign process will have a preferred place in the marketplace. Supplemental

Keywords:
small business, SBIR, metal deposition, surface deposition, microelectronics fabrication, CO2, solvent, barrier layer, seed layer, supercritical carbon dioxide, fluid displacement deposition process, organic ligands, EPA. , INTERNATIONAL COOPERATION, Scientific Discipline, Sustainable Industry/Business, Environmental Chemistry, Environmental Engineering, cleaner production/pollution prevention, pollution prevention, alternative electroplating, alternative metal finishing, alternative solvents, carbon dioxide, clean technology, cleaner production, electronics industry, electroplating, environmentally benign supercritical fluids, green design, industrial process

This proposal describes the application, development and commercial scale-up of a process successfully developed under EPA contract number EP-D-04-042 for the deposition of copper and copper barrier materials such as ruthenium, titanium and other metals. This process could replace CU 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 could also be replaced. The electroplating process generates large quantities of aqueous wastes with copper ions and other dangerous chemical that must be treated in place. The proposed process uses liquid or supercritical carbon dioxide 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 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 CO2solvent 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 carbon dioxide 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 which 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 place in the marketplace.