Buried-oxide layer formation by high-dose oxygen-ion implantation into Si wafers: SIMOX (separation by implanted oxygen)

Recent advances in SIMOX (separation by implanted oxygen) wafer technology are reviewed. Using a thin surface silicon layer (≤100 nm) should allow the improvement of transistor and integrated-circuit performance without the need for scaling-down. In the SIMOX process, silicon wafers are subjected to high dose oxygen-ion implantation (dose∼1×1018/cm2, energy ∼ 200 keV) and high-temperature annealing (≥1300°C). A buried-oxide layer (several hundred nm thick) is synthesized below a single-crystalline surface-silicon layer (several hundred nm thick). SIMOX structure may be synthesized using a super-stoichiometric oxygen concentration during implantation, or, more recently, a sub-stoichiometric oxygen concentration after annealing. The former method produces a reliable buried-oxide layer, but induces a high density of defects in the surface-silicon layer. The latter cuts implantation time and improves surface-silicon crystallinity, but process window is rather narrow.