No abstract

The characteristics of the formation and growth of buried oxide layers, formed by oxygen implantation into silicon at lower energies (50–140-keV 16O+), have been studied using secondary-ion mass spectrometry. Some results have been checked and compared with the results obtained by Rutherford backscattering and cross-sectional transmission electron microscopy. The critical doses, required to form a continuous buried stoichiometric oxide layer during implantation (ΦIc) and after annealing (ΦAc) have been estimated from experimental results. The thicknesses of the silicon overlayer (TASi) and buried silicon dioxide layer (TASiO2) for the annealed wafers have also been estimated. A set of semi-empirical formulas for ΦIc, ΦAc, TASi, and TASiO2 has been introduced. These formulas can be used to quickly calculate the critical doses and the layer thickness values.

The redistribution and electrical activity of implanted arsenic in separation by implanted oxygen (SIMOX) and bulk silicon substrates are compared. The SIMOX substrates were prepared by high dose oxygen implantation followed by high-temperature annealing. Subsequently doses of 5×1015 As+/cm−2 at 70 keV were implanted into the substrates and, also, bulk silicon. The samples were annealed to activate the arsenic. It was observed that (i) the same percentage activation was measured in both SIMOX samples and bulk silicon, (ii) no anomalous diffusion was seen in the SIMOX samples, and (iii) during further high-temperature annealing the buried oxide acts as a diffusion barrier. This data confirms the high quality of SIMOX material currently being prepared.

The generation of dislocations in silicon implanted by oxygen (SIMOX) is studied by transmission electron microscopy. In an effort to separate the effects of displacement damage caused by ion implantation from the dynamic structural transformation which occurs due to the insertion of oxygen into the lattice, two special experiments were designed. The first consisted of a series of low dose oxygen implantations in which the energy was either ramped up or down in small steps. This served to expand the region in which oxygen was implanted, permitting a more detailed study of the defects. The second experiment involved the implantation of oxygen into a (111) wafer in order to study the influence of the crystallographic orientation on the generation of dislocations. Both experiments reveal the important role of the surface in the generation of dislocations. It is concluded that most of the threading dislocations are formed during the high-temperature anneal and have their origin in a defect-rich zone near the surface. These defects are attributed to Si-interstitial migration to the surface which results from the formation of SiO2. Consequently, epitaxial growth takes place on the surface and due to the growth defects generated there, dislocations are extended to the Si overlayer during the high-temperature annealing. Dislocations are also formed in the Si overlayer near the interface with the SiO2 buried layer. These dislocations are pinned by the SiO2 precipitates and are either consumed or dragged by them to the oxide interface during subsequent high-temperature annealing. The effect of surface contamination on the generation of dislocations in the early stage of implantation is discussed and factors which yield a better quality SIMOX material are presented.

The critical doses required to form a continuous buried stoichiometric oxide layer for 70 keV oxygen implantation either during implantation, ΦnormalcI , or after implantation and annealing, ΦnormalcA are ≈7×1017 O+/cm2 and ≈3×1017 O+/cm2 , respectively. The dislocation density in the silicon overlayer and the distribution and density of silicon islands in the buried SiO2 layer of the annealed (70 keV) SIMOX (separated by implantation of oxygen) samples are strongly dependent on the oxygen dose (Φ) and the target temperature false(Tnormalifalse) . Good quality thin‐film SIMOX layers with a low threading dislocation density in the silicon overlayer and low density of silicon islands in the buried SiO2 layer have been produced by implantation of 3.3×1017 O+/cm2 at 680°C.