A GaN laser diode at is used to measure the velocity distribution function (vdf) of Ga atoms sputtered from a radio-frequency biased GaAs substrate in a low pressure inductively coupled plasma (ICP) argon discharge. To investigate both perpendicular ( normal to wafer) and longitudinal ( parallel to wafer) velocity components, laser induced fluorescence (LIF) measurements are performed in the direction and atomic absorption spectroscopy (AAS) in the direction. The longitudinal vdf of Ga sputtered atoms is very close to a Lorentzian function with comprised between 0 and , while the perpendicular velocities can reach . Experimental results are compared to molecular dynamics (MD) simulations of ion sputtering of GaAs under bombardment. MD predictions and experiments are in fairly good agreement, which confirms the existence of products sputtered from the surface with kinetic energies larger than . In etching processes dominated by physical bombardment, these energetic atoms could alter passivation layers on sidewalls and be responsible for defects observed in nanodevices. The best fit of the Doppler-broadened LIF and AAS profiles with the vdfs predicted by sputtering theory allows one to estimate the surface binding energy of Ga atoms in GaAs, , to be around .
Velocity distribution function of sputtered gallium atoms during inductively coupled argon plasma treatment of a GaAs surface
Emilie Despiau-Pujo, Pascal Chabert, Raphaël Ramos, Gilles Cunge, Nader Sadeghi; Velocity distribution function of sputtered gallium atoms during inductively coupled argon plasma treatment of a GaAs surface. J. Vac. Sci. Technol. A 1 March 2009; 27 (2): 356–361. https://doi.org/10.1116/1.3081967
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