A.K. Robinson

The role of implantation temperature and dose in the control of the microstructure of SIMOX structures

Abstract Single-crystal ⇇100↩ silicon wafers have been implanted with 200 keV oxygen ions over a dose range of 0.1×10 18 O + cm -2 to 1.4×10 18 O + cm -2 and a temperature range of ≈250°C to 550°C. The specimens have been analyzed, both before and after high-temperature annealing, using a variety of techniques, such as cross-sectional and planar Transmission Electron Microscopy (TEM), Rutherford backscattering (RBS), and ion channelling, Secondary Ion Mass Spectroscopy (SIMS), Infra-red Spectroscopy (IR), and Raman Spectroscopy. This has enabled us to evaluate the development of the SIMOX structure both with respect to implantation temperature and dose and also with respect to annealing temperature and time.

Analysis of thin‐film silicon‐on‐insulator structures formed by low‐energy oxygen ion implantation

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.

Formation of thin silicon films using low energy oxygen ion implantation

Abstract SIMOX (separation by implanted oxygen) is an established technique to produce device worthy silicon-on-insulator structures. Current interest in thin film fully depleted CMOS devices in SIMOX material has placed emphasis on producing silicon overlayers of 100 nm thickness or less. Thin film SIMOX substrates have been prepared using halogen lamps, to preheat and provide background heating during oxygen ion implantation in the relatively low energy range 50–140 keV. The resulting structures have been studied by RBS, cross-sectional TEM and SIMS. This paper reports on the crystalline quality of the silicon overlayers and discusses the viability of low energy oxygen implantation to produce thin film SIMOX structures suitable for VLSI device fabrication.

Dislocation formation related with high oxygen dose implantation on silicon

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 ...

The Effects of Dose and Target Temperature on Low Energy SIMOX Layers

The critical doses required to form a continuous buried stoichiometric oxide layer for 70 keV oxygen implantation either during implantation, Φ c 1 , or after implantation and annealing, Φ c A , are ≃7×10 17 O . /cm 2 and ≃3×10 17 O . /cm 2 , respectively. The dislocation density in the silicon overlayer and the distribution and density of silicon islands in the buried SiO 2 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 (T i )

Low energy, oxygen dose optimization for thin film separation by implanted oxygen

Low energy oxygen ions of 50 to 70 keV were implanted to doses of 1 × 1018 O+ cm−2 for the formation of separation by implanted oxygen (SIMOX) substrates. Owing to the reduced energy straggle of the low energy ions, it is possible to achieve a buried oxide layer with a lower dose (than with higher energies) which offers the potential advantage of a reduced fabrication cost for SIMOX material. However, defects, including threading dislocations and silicon islands near the lower SiO2Si interface, have been observed in low energy oxygen implanted material. A recipe to reduce the density of these islands is proposed, involving implantation of a dose of oxygen which is less than the critical dose Φc required to form a continuous layer of stoichiometric SiO2 during implantation. This not only reduces the density of silicon islands but also the ion implantation damage in the silicon overlayer is reduced and hence, after annealing, fewer threading dislocations (less than 105 cm−2) are present. The actual dose was determined experimentally for oxygen ions of energy 70 keV and a substrate temperature of 680 °C and was found to be approximately 0.33 × 1018O+ cm−2.

Nonplanar and noncontinuous buried layers of SiO2 in silicon formed by ion beam synthesis

Abstract The synthesis of buried layers of SiO2 by the implantation of high doses (1.8 × 1018O+ cm−2) of O+ ions through thick oxide masks is described. Due to the rapid sputter erosion of the SiO2 mask (1.1 atoms/particle) these layers grow, unlike conventional SIMOX structures, by the preferential growth (“internal oxidation”) of the lower SiO2/Si interface. It is shown that improved TDI structures may be formed by implantation into a thick (1.8 μm) oxide mask.

Dielectrically isolated silicon-on-insulator islands by masked oxygen implantation

A method of forming dielectrically isolated silicon‐on‐insulator device islands by using a thin patterned masking layer during implantation of high doses of oxygen into silicon is described. Due to energy loss in the masking layer, the oxygen ions synthesize both a surface oxide in the masked field regions and, simultaneously, a buried oxide in the unmasked windows. The field oxide is contiguous with the buried oxide under the device islands. This method of achieving total dielectric isolation has potential application in the fabrication of high‐density silicon‐on‐insulator circuits with a very flat topography.

Buried insulator formation by nitrogen implantation at elevated temperatures

Abstract Buried silicon nitride layers can be synthesized by high dose nitrogen implantation into silicon. To investigate temperature effects, 200 keV N + implantations into silicon were performed with doses of 0.35 to 1.05 × 10 18 N + cm −2 . A first set of samples was implanted at 500° C, using ion beam induced heating only. For the second set, a new sample holder provided constant background heating of the wafer maintaining it at a constant temperature of 670 ± 10° C by halogen lamp irradiation. Two hour anneals were carried out in flowing nitrogen at temperatures between 700 and 1200° C in 100° C steps. Rutherford backscattering measurements were performed in order to assess the quality of the silicon top layers. It is concluded that constant background heating leads to a major improvement of the crystalline quality for all implantation doses and for annealing temperatures up to 1100° C.

An investigation of Si0.5Ge0.5 alloy oxidation by high dose oxygen implantation

Abstract An attempt to implant a high dose (up to 1.8 × 1018 cm−2) O+ ions into a Si0.5Ge0.5 alloy grown by molecular beam epitaxy (MBE) was made in this work, and the oxidation of the alloy by the implantation before and after thermal treatment was studied using X-ray photoelectron spectroscopy (XPS). The changes of the composition distribution in the sample were observed from the XPS depth profiles. The chemical states of Si and Ge as well as the location of their oxides were obtained from the spectrum fitting. The results indicate that compared to the implantation made on single crystal Si or Ge, this alloy seems to have more in common with the bulk Si and the reason is attributed to the different reactivities between Si and Ge with oxygen and the different stabilities of their oxides. A possible way to improve the experiment to achieve the SIMOX (separation by implanted oxygen) structure in this material is also suggested.