The fracture strength of nitrogen doped silicon wafers

With a specially designed double ring bending setup, we have studied the room temperature fracture strength of silicon wafers prepared by standard manufacturing methods with both (as) cut, (as) lapped, and (as) polished surfaces. Wafers from six different crystals have been tested. The differences between these crystals are related to growth method (float zone or Czochralski), concentration of light element impurities (nitrogen and oxygen), and further processing (neutron irradiation and thermal annealing). No significant differences in strength between crystals of different origin can be revealed on wafers prepared with (as) cut and (as) lapped surfaces. Polished wafers generally show a fracture strength of the order of 1 GPa, with a large scatter between single measurements. No differences between the strength of polished wafers from float zone (FZ) and Czochralski (CZ) crystals can be detected, but the median strength of a FZ crystal with small concentrations of both nitrogen and oxygen is observed to have a much higher value of 2.5 GPa.