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Energy and momentum transfer in scattering of low-energy atoms on metal surfaces
A458 Surface Science 123 (1982) 427-438 North-Holland Publishing Company
427
A SIMS STUDY OF ION-ASSISTED ETCHING MECHANISMS; A D S O R B E D FLUORINE ON Si R E M O V E D BY ION BOMBARDMENT E.-A. KNABBE
*, J . W . C O B U R N
and
E. K A Y
IBM Research Laboratory, San Jose, CahJbrnia 95193, USA Received I1 June 1982; accepted for publication 21 September 1982 Secondary ion mass spectrometry (SIMS), previously calibrated using quartz crystal microbalance (QCM) methods, has been used to measure the cross-section for ion-bombardment-induced removal of fluorine adsorbed on silicon. Large (100 A2) cross-sections have been found at high fluorine coverages. It is believed that ion bombardment of the adsorbed fluorine layer forms relatively large quantities of volatile silicon fluorides which spontaneously desorb from the surface. At low fluorine coverages, where the cross-sections are much smaller (5-10 A2). there is insufficient fluorine to form volatile silicon fluorides and the adsorbed fluorine must be removed primarily by physical sputtering. This phenomenon of ion-bombardment-induced gasification or ion-induced clearing of adsorbed layers is believed to be responsible for the ion-enhanced gas-surface chemistry observed in directed beam studies involving fluorine and silicon. Furthermore, it is suspected that many of the observations of anisotropic etching in reactive gas glow discharges may be caused by this process.
439
Surface Science 123 (1982) 439-455 North-Holland Publishing Company
ENERGY A N D M O M E N T U M LOW-ENERGY
ATOMS
ON
TRANSFER METAL
IN SCATI'ERING OF
SURFACES
R. BRAKO
Department of Mathematics, Imperial College of Science and Technology, London SWT, C!K and Rudjer Bogkovi6 Institute, 41001 Zagreb, Croatia, Yugoslavia * Received 3 March 1982; accepted for publication 24 September 1982 The scattering of low-energy atoms on metal surfaces is investigated theoretically, assuming that the adatom motion is coupled to surface phonons. The trajectory approximation is used. In the strong-coupling regime, in which m a n y phonons are excited in the course of a scattering event, the results simplify considerably and take a universal form. Essentially, only one unknown parameter remains, the average energy loss 8, which can be determined by comparison with experiments. Details of the phonon dispersion relation and of the coupling constants are lost in the superposition of energy and m o m e n t u m transfers of a large number of pbonons. Explicit expressions for the scattering cross section are derived in this limit. The approach is very successful in analysing the angular and energy distributions of the direct fraction of heavy noble-gas atoms (Ar, Kr, Xe) scattered on metal surfaces.
427
A SIMS STUDY OF ION-ASSISTED ETCHING MECHANISMS; A D S O R B E D FLUORINE ON Si R E M O V E D BY ION BOMBARDMENT E.-A. KNABBE
*, J . W . C O B U R N
and
E. K A Y
IBM Research Laboratory, San Jose, CahJbrnia 95193, USA Received I1 June 1982; accepted for publication 21 September 1982 Secondary ion mass spectrometry (SIMS), previously calibrated using quartz crystal microbalance (QCM) methods, has been used to measure the cross-section for ion-bombardment-induced removal of fluorine adsorbed on silicon. Large (100 A2) cross-sections have been found at high fluorine coverages. It is believed that ion bombardment of the adsorbed fluorine layer forms relatively large quantities of volatile silicon fluorides which spontaneously desorb from the surface. At low fluorine coverages, where the cross-sections are much smaller (5-10 A2). there is insufficient fluorine to form volatile silicon fluorides and the adsorbed fluorine must be removed primarily by physical sputtering. This phenomenon of ion-bombardment-induced gasification or ion-induced clearing of adsorbed layers is believed to be responsible for the ion-enhanced gas-surface chemistry observed in directed beam studies involving fluorine and silicon. Furthermore, it is suspected that many of the observations of anisotropic etching in reactive gas glow discharges may be caused by this process.
439
Surface Science 123 (1982) 439-455 North-Holland Publishing Company
ENERGY A N D M O M E N T U M LOW-ENERGY
ATOMS
ON
TRANSFER METAL
IN SCATI'ERING OF
SURFACES
R. BRAKO
Department of Mathematics, Imperial College of Science and Technology, London SWT, C!K and Rudjer Bogkovi6 Institute, 41001 Zagreb, Croatia, Yugoslavia * Received 3 March 1982; accepted for publication 24 September 1982 The scattering of low-energy atoms on metal surfaces is investigated theoretically, assuming that the adatom motion is coupled to surface phonons. The trajectory approximation is used. In the strong-coupling regime, in which m a n y phonons are excited in the course of a scattering event, the results simplify considerably and take a universal form. Essentially, only one unknown parameter remains, the average energy loss 8, which can be determined by comparison with experiments. Details of the phonon dispersion relation and of the coupling constants are lost in the superposition of energy and m o m e n t u m transfers of a large number of pbonons. Explicit expressions for the scattering cross section are derived in this limit. The approach is very successful in analysing the angular and energy distributions of the direct fraction of heavy noble-gas atoms (Ar, Kr, Xe) scattered on metal surfaces.