The cause of Si recess (i.e., formation of shallow hollows on a Si surface after removal of an oxide layer from the Si surface in a polycrystalline silicon gate etching process by a HBr plasma) was identified as ion-assisted oxygen diffusion (oxygen-diffusion enhanced by hydrogen ion bombardment from the plasma). Both plasma and multi-beam experiments were employed for the analysis of this oxidation mechanism. It was also found in the analysis that oxidation of a Si surface exposed to oxygen radicals was significantly enhanced only if the surface was subject to both oxygen radical supply and energetic hydrogen ion bombardment simultaneously.

Si Recess of Polycrystalline Silicon Gate Etching: Damage Enhanced by Ion Assisted Oxygen Diffusion. T.Ito, K.Karahashi, M.Fukasawa, T.Tatsumi, S.Hamaguchi: Japanese Journal of Applied Physics, 2011, 50, 08KD02