The effect of ultrasonic treatment (UST) on the defect structure of the Si–SiO₂system by means of electron spin resonance (ESR),selective etching, MOS capacitance technique and secondary ions masspectroscopy is presented. The non-monotonous dependence of the defect densities on the US wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres depended on the defects type and may be caused by vibration energy dissipation, which are a function of defect centres type.In the ESR spectra of Si samples a signal with g=1.9996 (P a centers) connected with vacancy complexes is observed. After UST appears another signal with g=2.0055 (broken bonds of Si atoms) . The influence of the US frequency and sample orientation on the ESR signal intensity varies for different centres. The frequency and orientation dependence of the ESR signal with g=l.9996 and the lack of this dependence for the centres with g=2.0055 show that vibration energy dissipation depends on the type of defect centers.Defect density at the interface grows with an increase of US wave intencity or changes non-monotonously depending on the oxide thickness and crystallographic orientation. In the samples with thick oxide there is a maximum in the dependence of the charge carriers lifetime on the US wave amplitude and in the samples with thin oxides-there is a minimum.This shows that the structural defects form electrically active centers and their density can be varied by US.The density of point defects and absorbed impurities at the Si–SiO₂interface can be reduced and its electrical parameters improved by an appropriate choice of the UST and oxidation condition.US is widely used not only for materials treatment but in medicine as well (cancer treatment).

References:

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