FORMATION OF SI3N4 DURING THE DIRECT NITR IDATION OF SI SINGLE-CRYSTAL

Single crystal Si was nitrided in a fluidized-bed reactor. The volume fraction of the alpha/beta phases and the nitridation process were stu died by X-ray diffraction and electron microscopy. No difference in th e alpha/beta ratio and the nitridation rate were found between pure Si single crystal and commercial Si powder including impurities. This in dicates that the alpha/beta ratio is not affected by the impurity cont ent. Microstructural observation revealed the internal fracture of Si to several-micron pieces and the formation of Si3N4 needles in the ear ly stage of nitridation. Pores were also observed in the fractured Si pieces and the size increased with the progress of nitridation. Aggreg ation of Si3N4 in a band shape and a group of dislocations, forming sm all angle boundaries, were also observed in the Si piece. The fracture of the Si single crystal appears to be caused by segregation of nitro gen along dislocations, introduced during fluidization, and subsequent formation of Si3N4.