Chemical interaction of NF3 ion beams and plasmas with Si (Part I): X-ray photoelectron spectroscopy studies

The interaction of nitrogen trifluoride (NF3) with silicon (Si) surface has been investigated by X-ray photoelectron spectroscopy (XPS). Si(100) surfaces were subjected to NF3 ion beams under controlled conditions. Samples were also exposed to actual NF3 d.c. plasmas, and the results were compared with the ion-beam irradiations with their doses chosen to match the expected ion dose in the plasmas. The novel use of the NF3-generated ion beams allowed an independent investigation of the ion effects in the NF3 plasmas, and we have been able to differentiate the role of both ions and neutrals in NF3 plasma etching of Si. Both ion-beam and plasma experiments indicate that etching, nitridation and fluorination of Si occur simultaneously. In the ion-beam chemical interaction with Si, there is evidence of the formation of a complex SiNF moiety, as identified by a F 1s peak that appeared at 687.4 eV. This location was shifted by ∼1.8 eV to a higher binding energy side than that normally observed in the reaction between F and Si. Nitrogen trifluoride plasma interaction with Si replicates this complex moiety, but also forms SiFx species that are ascribed to a neutral FSi interaction. Interpretation and rationalization of the peak positions were made simply on the expected charge on each atom based on the Pauling electronegativity.