Hydrogen-plasma etching of ion beam deposited c-BN films: An in situ investigation of the surface with electron spectroscopy

Abstract

In the present study nanocrystalline c-BN films deposited with a mass selected ion beam were subjected to a hydrogen plasma or atomic hydrogen produced by the hot filament method. Film composition and electronic properties of the surface were subsequently analyzed in situ by photoelectron spectroscopy in the x-ray and ultraviolet regime, and by electron energy loss spectroscopy. The sp(2)-bonded surface layer, which is native to ion beam deposited c-BN films, is rapidly removed by hydrogen plasma etching and the almost phase pure c-BN layer uncovered. Continuation of hydrogen plasma exposure leads to a removal of the c-BN layer at an etch rate of about 0.65 nm/min until finally the sp(2)-BN nucleation layer is detected. No preferential etching of either B or N is observed and an equal concentration of the constituents is maintained throughout the experiment. The large atomic hydrogen flux from the plasma is held responsible for the efficient etching, which could not be achieved with the hot filament method. The valence band spectra of nanocrystalline c-BN can be understood in the framework of published density of states calculations and allows to identify characteristic spectral features for both phases. The nanocrystalline c-BN surface exhibits a negative electron affinity, which might be connected to a hydrogen termination of the surface. The hydrogen plasma etching offers a comparatively easy route for future investigations of surface reactivity and the exploitation of the NEA property of the material. (C) 2000 American Institute of Physics. [S0021-8979(00)05623-1].