Si Recess of Polycrystalline Silicon Gate Etching: Damage Enhanced by Ion Assisted Oxygen Diffusion

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) has been identified as ion assisted oxygen diffusion, i.e., 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 has been also found in the analysis that oxidation of a Si surface exposed to oxygen radicals is significantly enhanced only if the surface is subject to both oxygen radical supply and energetic hydrogen ion bombardment simultaneously.