H+ AND D+ ASSOCIATED CHARGE BUILDUP DURING ANNEALING OF SI SIO2/SI STRUCTURES/

Si/SiO2/Si structures produced by high temperature processing have bee n 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 te mperatures 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 bu t must be attributed to protons or deuterons. Both static and mobile s pecies are formed dependent upon the confined (Si/SiO2/Si) or unconfin ed (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 mobi le ions with an activation energy estimated to be 0.81 +/- 0.02 eV bot h 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 t hemselves to oxygens in strained Si-O-Si bonds near the Si/SiO2 interf ace, the positive charged state is stabilised by loss of an electron t o the Si conduction band. It is assumed that strongly bound over coord inated oxygens near the interface constitute the fixed oxide charge sp ecies 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 Scie nce B.V.