Plasma/reactor walls interactions in advanced gate etching processes

Wafer-to-wafer reproducibility is a major challenge in gate etching processes. Periodic dry cleaning of the reactor in F-based chemistry between wafers is the most common strategy to ensure process repeatability. However X-ray Photoelectron Spectroscopy analysis of the chamber walls show that this cleaning procedure leaves AlFx species on the reactor walls, eventually resulting in process drifts and formation of particles. We have thus investigated a new cleaning/conditioning strategy of plasma etching reactors, in which the chamber walls are coated by a carbon-rich film between each wafer, allowing stable processing conditions and highly anisotropic etching profile to be achieved in advanced gate stacks. Finally, we present a new method (based on the detection of Cl2 by laser absorption) to characterize the reactor walls conditions that could prevent process drifts.