Proton-induced defect generation at the Si-SiO2 interface

We report first-principles calculations of interface trap formation in MOS structures. Hydrogen is known to passivate Si dangling bonds at the Si-SiO₂ interface, but the subsequent arrival of H+ at the interface causes depassivation of Si-H bonds. We show that, contrary to conventional assumptions, depassivation is not a two-step process, namely, neutralization of H+ by a Si electron, reaction with a Si-H bond, and subsequent formation of an H₂ molecule. Instead, we establish that H+ is the only stable charge state of hydrogen at the interface, and that H+ reacts directly with Si-H. The products of this reaction are an H₂ molecule and a positively charged dangling bond center (D⁺), formed via the reaction SiH + H⁺ ⇒ D⁺ + H₂. Here the D⁺ center is most likely the positive charge state of the P _b defect. As a result, H-induced interface-trap formation depends on the electric field in the oxide to establish a preferred direction for proton drift, but does not depend on the availability of Si electrons to enable the interface reaction to occur. After the dangling bond center is formed via this process, the subsequent charge state of the interface traps is controlled by the Si surface potential. A hydrogen catalytic cycle can lead to reversible passivation and depassivation reactions at or near the interface, depending on experimental conditions