Ga. Kachurin et al., ROLES OF IMPLANTATION TEMPERATURE AND ION DOSE-RATE IN ION-BEAM SYNTHESIS OF BURIED SI3N4 LAYERS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 74(3), 1993, pp. 399-404
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.