H+ and D+ associated charge buildup during annealing of Si/SiO2/Si structures

Si/SiO2/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 degrees C. For temperatures greater than or equal to 500 degrees C spontaneous positive electrical charging in the SiO2 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/SiO2/Si) or unconfined (SiO2/Si) nature of the structure of the sample. Application of an electric field similar to 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 root 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 over coordinated oxygen atoms with the H or D attaching themselves to oxygens in strained Si-O-Si bonds near the Si/SiO2 interface, the positive charged state is stabilised by loss of an electron to the Si conduction band. It is assumed that strongly bound over coordinated 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. (C) 1997 Elsevier Science B.V.