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

This work investigates the potential application of magnesium fluoride (MgF_x) films and compares its effectiveness to conventional silicon nitride (SiN_x: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 MgF_xcoated samples is fully activated only at 600 °C, whereas passivation in SiN_x: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 MgF_xfilms 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 SiN_x:H passivated samples than in MgF_xpassivated 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 SiN_x:H passivated samples. Based on these observations, we suggest the possibility that the dominant passivating agent in the MgF_xand SiN_x:H films is fluorine and hydrogen, respectively. Finally, minority carrier lifetime measurements indicate that both the passivation methods improve the bulk lifetime significantly.