New SiOH complexes and proton release mechanism in silica as a source of Si/SiO$_{2}$ interface-trap build up

Water molecules in SiO$_{2}$ have been studied extensively in the context of reliability of electronic devices. Here we report results of new density-functional first-principles calculations and experimental data that demonstrate a key role of H$_{2}$O molecules in the long-term degradation of MOSFETs by increases in interface-trap densities. A new low energy complex formed by H$_{2}$O has been identified. The complex consists of two SiOH groups located on neighboring rings. The energy of the complex is 0.3 eV lower than that for the free interstitial water molecule in the ring of $\sim $ 0.7 nm. The two silanol groups have different local topology, which results in different ability of the SiOH elements to capture holes and release protons under X-irradiation. The release of H$^{+}$ has a barrier of the reaction $\sim $ 0.45 eV and is accompanied by creation of a peroxy-type structure inside network ring. The released protons can diffuse or drift (driven by electric fields) to the interface, where they depassivate dangling bonds by forming H$_{2}$ molecules. We will present experimental data on the radiation response of devices that have been in storage for 20 years. The results are consistent with the theoretical picture, when water molecules are responsible for a substantial increase of interface-trap densities over time.