H + and D + associated charge buildup during annealing of Si/SiO 2/Si structures

Abstract

Si/SiO 2/Si structures produced by high temperature processing have been annealed in atmospheres containing forming gas (5% H 2, 95% N 2 or 5% D 2, 95% N 2) at temperatures in the range 200–900°C. For temperatures ≥ 500°C spontaneous positive electrical charging in the SiO 2 layer is observed. Electron and hole injection experiments confirm that the charging is not due to holes but must be attributed to protons or deuterons. Both static and mobile species are formed dependent upon the confined (Si/SiO 2/Si) or unconfined (SiO 2/Si) nature of the structure of the sample. Application of an electric field ∼ 10 5 V cm −1 results in motion of the mobile ions with an activation energy estimated to be 0.81 ± 0.02 eV both for deuterons and protons. A √mass factor is evidenced resulting in the conclusion that the protons are more mobile than the deuterons. The physical origin of the charging phenomenon is attributed to the formation of overcoordinated oxygen atoms with the H or D attaching themselves to oxygens in strained SiOSi bonds near the Si/SiO 2 interface, the positive chargeds state is stabilised by loss of an electron to the Si conduction band. It is assumed that strongly bound overcoordinated oxygens near the interface constitute the fixed oxide charge species while more weakly bound forms migrating from SiOSi unit to SiOSi unit are the origin of the mobile species.