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

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. 51, 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.