Interface-trap transformation at radiation-damaged (111)Si/SiO2 interface

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Abstract
This letter presents the results of our recent study on the post‐irradiation behavior of the interface trap distribution in metal‐SiO2‐Si capacitors made on Si substrates of (111) orientation. It will be shown that the interface trap distribution in these (111) samples measured immediately after x‐ray irradiation is qualitatively similar to what was observed in the (100) counterpart: a prominent peak appears in the upper half of the Si band gap (Ev+0.75 eV). Subsequent time‐dependent evolution behavior of this peak, however, is distinctly different for samples with the two different orientations. While in (100) samples a second peak in the lower half of the band gap would develop over time, resulting in a double‐peak interface trap distribution [see, for example, E. F. da Silva, Y. Nishioka, and T.‐P. Ma, Appl. Phys. Lett. 5 1, 270 (1987)], the most salient feature observed in (111) samples is the gradual shift of the peak position with time toward the lower half of the Si band gap, and eventually a single peak will reside below midgap. The movement of this peak has been found to be thermally accelerated, with an apparent activation energy of about 0.4±0.1 eV. It has also been found that the gate‐induced compressive strain at the Si/SiO2 interface plays an important role in the peak movement. In addition, the presence of a gate bias and its polarity also significantly affect the post‐irradiation behavior of the interface trap distribution. The results may be explained in terms of the atomic relaxation of the bonding defect at the (111)Si/SiO2 interface.

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