The Semiconductor Industry Association's International Technology Roadmap for Semiconductors currently indicates that no viable means for depositing copper (Cu) below 100nm exists. But a team at the University of Massachusetts has developed a process called chemical fluid deposition (CFD) that meets the criteria.
The team has developed a technique that uses neither liquid nor gas to deposit the layer on to the substrate. Instead, it uses a supercritical fluid, which has some properties of a liquid and some of a gas.
Dr James Watkins, chemical engineer and the team leader, said: "We take the best of vapour phase techniques and liquid phase techniques and combine them."
The problem facing 100nm copper deposition is filling the narrow structures evenly and completely. The team claims to have solved this by developing a technique that efficiently deposits device quality copper and nickel films for use in interconnections.
The copper is deposited on to the substrate during CFD by the reduction of CO2 solutions of either Cu(I) or Cu(II) organometallic compounds in a high-pressure, cold-wall reactor. The substrate is heated to a higher temperature than the solution and the copper is deposited on to the heated area.
The team is developing the technique for other applications including gas separation devices and photonic materials.