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

In the present study nanocrystalline c-BN films deposited with a mass selec ted ion beam were subjected to a hydrogen plasma or atomic hydrogen produce d by the hot filament method. Film composition and electronic properties of the surface were subsequently analyzed in situ by photoelectron spectrosco py in the x-ray and ultraviolet regime, and by electron energy loss spectro scopy. The sp(2)-bonded surface layer, which is native to ion beam deposite d c-BN films, is rapidly removed by hydrogen plasma etching and the almost phase pure c-BN layer uncovered. Continuation of hydrogen plasma exposure l eads to a removal of the c-BN layer at an etch rate of about 0.65 nm/min un til finally the sp(2)-BN nucleation layer is detected. No preferential etch ing of either B or N is observed and an equal concentration of the constitu ents is maintained throughout the experiment. The large atomic hydrogen flu x from the plasma is held responsible for the efficient etching, which coul d not be achieved with the hot filament method. The valence band spectra of nanocrystalline c-BN can be understood in the framework of published densi ty of states calculations and allows to identify characteristic spectral fe atures for both phases. The nanocrystalline c-BN surface exhibits a negativ e 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. [S00 21-8979(00)05623-1].