Applications and computational fluid dynamics study of supercritical fluid processes
The development of microelectronics, optoelectronics and data storage requires new thin solid film deposition techniques, which could fulfill the requirement of conformal coverage on complex surfaces. Supercritical Fluid Deposition (SFD) is a process that combines the advantages of gas-phase and liquid-phase deposition techniques due to the properties of supercritical fluids. Compared to the existing deposition techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), SFD is able to deposit films at lower temperature and get conformal coverage even for high aspect ratio features. And the deposition speed of SFD is much faster than atomic layer deposition (ALD).
Copper is the preferred interconnect material in the microelectronics industry because of its lower resistivity and higher electron migration resistance in comparison to aluminum and its alloys. The use of copper reduces the signal transmission delay and improves reliability relative to aluminum. However copper is easily oxidized and forms the thin layer of native cuprous oxide when exposed to air. In this work, etching of cuprous oxide from Cu or SiO 2 substrates in supercritical CO2 using β-diketone etching agents is effective and efficient. Etching with trimethyloctanedione (TMOD) at 150°C proceeds at a rate of 15 Å/min with an activation energy of 66 kJ/mol. The formation of Cu2+ including CuO and Cu(OH) 2 at the surface of Cu2O during ambient exposure appears to form a passivation layer that initially inhibits CuO etching.
Supercritical fluid cold wall reactors have been used for different areas of microelectronics industry. To understand the heat transfer and flow patterns inside the reactor, CFD studies have been carried out. A simple theoretical analysis indicated natural convection is very strong and turbulent within cold wall supercritical fluid deposition reactors due to the highly temperature dependent properties of SC CO2. Two 2D prototype simulations have been carried out to study the effects of the reactor clearance above the heater on the thermal profiles. It has been clearly demonstrated that enough clearance is critical for an even temperature distribution. It also is evident that in continuous running mode, the flow is dominated by natural convection. Two cold wall reactors with different operating modes: continuous and batch have been investigated. In three dimensions simulations, temperature variations on the heater surface have been successfully simulated. The use of the liner material to protect the reactor wall has been shown to be effective. It was also shown that the inlet flow for the continuous reactor does not impinge on the heated platen due to the strong natural convection. Different liner materials have been used in the experiments and the insulation effects have been compared. The showerhead design for the top liner cover to distribute the fresh SC CO2 flow has been simulated; the effect of it has been tested. Suggestions for better design of the top cover liner have been proposed.