Passivation of Ring Defects in Czochralski-Grown Silicon Using Magnesium Fluoride Films

Abstract

This work investigates the potential application of magnesium fluoride (MgFx) films and compares its effectiveness to conventional silicon nitride (SiNx:H) for passivating ring defects, which sometimes occur in n-type Czochralski-grown silicon wafers subjected to high-temperature processes. We find that the passivation of ring defects in MgFx coated samples is fully activated only at 600 °C, whereas passivation in SiNx:H coated samples can be activated by 5 min anneals at 500 °C. Consistent with the passivation activation temperature, energy-dispersive X-ray shows that MgFx films significantly lose fluorine at temperature ≥ 600 °C. Further, subsequent annealing of the previously passivated samples reveals that the ring defects reappear and become recombination-active again. However, this depassivation of the ring defects occurs significantly faster in SiNx:H passivated samples than in MgFx passivated samples at temperatures ≤ 500 °C, whereas the depassivation happens at a rate similar to that at temperatures ≥ 600 °C. Furthermore, in situ monitoring of the change in band–band photoluminescence intensity during annealing also confirms that the passivation and depassivation of ring defects is faster in SiNx:H passivated samples. Based on these observations, we suggest the possibility that the dominant passivating agent in the MgFx and SiNx:H films is fluorine and hydrogen, respectively. Finally, minority carrier lifetime measurements indicate that both the passivation methods improve the bulk lifetime significantly.