First principles study of Si etching by CHF3 plasma source

A model of CF3 etching Si (2 × 4) surface has been developed based on density functional theory. We find that the reconstruction Si surface tends to be fully F-terminated. Meanwhile, C–C chain forms spontaneously on the top of the surface to resist further F–Si interacting. Over-saturated Si bonds could still be stable as well due to the strong F–Si bonding, however, it needs to overcome an energy barrier of 1.85 eV to achieve this doubly saturated bonding. Two reaction paths are found to investigate chemical reaction of CF3 with the full F-terminated Si surface. The first path displays that all fully saturated F–Si bonds could be over-saturated and thus produce F–Si–F bonds with an energy barrier of ∼1.85 eV. For this path, there is no product of SiF4; the second path indicates a formation of SiF4 with a much lower surface energy than the first path. The formation of SiF4 shows the possible etching mechanism.