ROLES OF IMPLANTATION TEMPERATURE AND ION DOSE-RATE IN ION-BEAM SYNTHESIS OF BURIED SI3N4 LAYERS

High doses of 135-150 keV N+ ions were implanted in silicon using low (j = 3-5 muA/cm2) and high (j = 100 muA/cm2) dose rates. Target temper ature interval was from T(i) = 600 to 900-degrees-C. The implanted sam ples were examined by IR transmission spectroscopy, TEM and light refl ection spectroscopy. At T(i) < 700-degrees-C, implantations produced a morphous buried layers. Above 700-degrees-C, but still much lower than the normal nitride crystallization temperature, formation of numerous Si3N4 Crystallites was observed. Low j caused the formation of alpha- Si3N4 Precipitates and provided for the growth of single-crystal matri x-oriented buried alpha-Si3N4 layers during post-implantation annealin g. High j implantations led in the early stages to the formation of mo re than 10(11) cm-2 tiny beta-Si3N4 precipitates which enlarged and co mbined with increasing dose. It is assumed that the role of T(i) is in providing sufficient mobility to the nitrogen atoms and suppression o f defect accumulation in silicon. An increase in j favours the accumul ation of defects, which serve as nucleation sites for nitride, and enh ances the supply rate of nitrogen atoms to the growing precipitates. T hus, low j implantations result in the formation of a-Si3N4 better ada pted to the Si matrix and allow single-crystal buried nitride layers t o be obtained after annealing. Under high j the silicon lattice fails to orient the growing nitride, therefore the energetically more favour able beta-phase forms.