Microvoid Defects in Nitrogen- and/or Carbon-doped Czochralski-grown Silicon Crystals

Microvoid defects in nitrogen- and/or carbon-doped Czochralski-grown silicon crystals grown under various growth conditions were investigated by transmission electron microscopy. The morphology and volume of the void defects depended strongly on the nitrogen concentration and the cooling rate. With increasing nitrogen concentration, the shape of the voids changed from {111} octahedron to {111} parallelepiped-plate or -rod via an unfaceted structure. The average volume of the voids decreased exponentially with the increase in nitrogen concentration. On the other hand, multiple voids consisting of octahedral segments, whose average volume is small, were observed in carbon-doped crystals. In nitrogen- and carbon-codoped crystals, multiple voids consisting of plate and rod segments were observed, whose average volume was very small. The thickness of the inner oxide layers of voids was influenced by the cooling rate, and not by nitrogen and carbon. From these results, it was assumed that nitrogen and carbon play different roles in the void formation. The change of void morphology by nitrogen-doping is discussed in terms of anisotropic void growth.