X-ray photoelectron spectroscopy analysis of the effect of temperature upon surface composition of InP etched in Cl-2-based inductively coupled plasma
Résumé
The chemical composition of the surface of InP samples etched in Cl-2 and Cl-2/Ar inductively coupled plasma (ICP) is analyzed using ex-situ x-ray photoelectron spectroscopy (XPS). Comparison between ex-situ and in-situ XPS measurements shows that the stoichiometry of the etched surface can be retrieved from the ex-situ analysis provided that an adapted procedure is used. This allows for investigating the evolution of the surface stoichiometry as a function of etching parameters. The sample temperature is found to play a determining role in the top surface composition during etching. An abrupt switch from a rough and In-rich surface to a smooth and significantly P-rich surface is observed above a critical temperature and is found to depend only weakly upon the other etching parameters such as direct current bias or pressure. Ex-situ XPS measurements are used to estimate the thickness of the phosphorus layer identified on the top surface as similar to 1 nm, which is consistent with the value previously derived using in-situ XPS. Finally, the stoichiometry of the InP etched sidewalls is analyzed selectively using dedicated microscale periodic patterns. The surface P-enrichment of the etched sidewalls is found to be very similar to that of the bottom etched surface. The presence of the phosphorus top layer may have an impact on the sidewall passivation mechanism during anisotropic ICP etching of InP-based heterostructures using Cl-2-containing plasma chemistry.