3.2 Centers

Figure 3.7: Possible configurations of an oxide trapping center as found in amorphous . It comprises of an unpaired electron localized on a silicon atom which is back-bonded to either three oxygen atoms (a) or two oxygen and one hydrogen atoms (b).

$\ensuremath{E'}_\mathrm{s}$

$\ensuremath{E'}_\mathrm{74}$

Figure 3.8: Other possible configurations of centers. They comprise of a second silicon atom impacting the defect.

$\ensuremath{E'}_\mathrm{\delta}$

$\ensuremath{E'}_\mathrm{\gamma}$

Another defect, found in close to the interface, is the center oxide defect. The exact atomic configuration is still debated [27,17,36,37,38] but possible configurations of centers involve an unpaired electron localized on a silicon atom back-bonded to three oxygen atoms or two oxygen atoms and one hydrogen atom, as shown in Figure 3.7. Variants proposed include a second silicon atom impacting the defect as depicted in Figure 3.8.

After very harsh negative bias temperature stressing conditions, those defects can be detected using resonance measurements [22,18]. SDR measurements are only capable of sensing near interface oxide defects, as only those can interact with the interface traps and alter the recombination current. Therefore it is not clear whether more defects are located deeper in the .

centers have levels near the middle of the band-gap where they allow hole capture from the silicon inversion layer. It was shown experimentally [36] that after hole capture an center can crack molecular hydrogen. This process might be important for the dissociation of silicon-hydrogen bonds at the interface and therefore for the effect of NBTI.