Thomas Schwarze

Feasibility Study for Usage of Diluted Fluorine for Chamber Clean Etch Applications as an Environmental Friendly Replacement of NF 3

Deposition steps in CVD and ALD applications usually not only cover the surface of the substrate surface but also the walls of the chamber inside. Regular removal of those residuals has to be done to obtain stable and repeatable deposition results with uniform surfaces at acceptable particle levels. The high requirements to sustain stable processes has lead to more frequent chamber cleans. NF 3 has emerged as the main clean gas for remote clean applications. While it meets the above mentioned requirements and is considered to fit easily into the fab gas supply it is relatively expensive. The work presented here investigates argon/nitrogen diluted fluorine (F 2 ) as an alternative clean gas with a significantly reduced environmentally destructive global warming emission (GWP). The cleaning behaviour with respect to different materials (SiON, TaN, TiN, W, SiO 2 ) was studied. It is found that in general argon/nitrogen diluted fluorine achieves etch rates comparable to those obtained by NF 3 when the comparison is based on the amount of fluorine transported into the reactor.

Superior etch performance of Ar/N 2 /F 2 for PECVD chamber clean

F<inf>2</inf> gas mixtures offer ideal properties to be employed as chamber cleaning gas: low dissociation energy and high reactivity, which leads to superior efficiency and ease of abatement. In this work, a new F<inf>2</inf> gas mixture was used with a combination ratio of 10% Ar, 20% F<inf>2</inf> and 70% N<inf>2</inf> in order to obtain a maximum of 20% fluorine in inert gases. This novel Ar/N<inf>2</inf>/F<inf>2</inf> gas mixture has been evaluated as a candidate to replace conventional cleaning gases, like NF<inf>3</inf>, C<inf>2</inf>F<inf>6</inf> and CF<inf>4</inf> in an industrial AMAT P5000 CVD chamber tool. Standard equipment has been used, showing complete compatibility with the new gas. The tested Ar/N<inf>2</inf>/F<inf>2</inf> mixture shows improvements in both parameters, cleaning at a faster rate (up to more 27%), even requiring a lower amount of gas (minus 96% versus NF<inf>3</inf>). The higher etching rate and the lower gas consumption assure a sensible CoO (Cost of Ownership) advantage to any potential user. The superior etch rate performance of the Ar/N<inf>2</inf>/F<inf>2</inf> gas mixture was combined with excellent etch non uniformities values, of °3% (1sigma) on SiO<inf>2</inf> and of °8% (1sigma) on Si<inf>3</inf>N<inf>4</inf>, respectively. Also amorphous Silicon (a-Si) was etched completely and uniformly. The particle performance data showing in average just 14 particle adders (0.25µm), indicating that no significant particle contamination was induced by the process and Ar/N<inf>2</inf>/F<inf>2</inf> can be used as a highly clean and efficient etching gas as well as an ideal drop-in replacement for the conventional cleaning gases.