C.D. Marsh

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.

Ion beam synthesis of thin buried layers of SiO2 in silicon

New experiments are reported which explore the possibility of using ion implantation to form thin (<2000 A) buried layers of stoichiometric SiO2 in single crystal silicon, Silicon (100) wafers have been implanted with O+ ions within the dose range 0.1×1018–1.8×1018O+ cm−2 at a particle energy of 200 keV and a substrate temperature of 500°C. Both (100) channelled and non-channelled implants have been carried out. Samples were subsequently annealed at temperatures of up to 1405°C, which causes the oxygen to segregate near the peak of the implanted oxygen distribution. The high dose samples have a continuous buried oxide layer whose thickness scales with the implanted dose, whilst in samples implanted with 0.1×1018O cm−2, discrete, strain free polyhedral precipitates, of diameter 500–1600 A, grow within the single crystal silicon matrix, by a mechanism which is qualitatively similar to oxygen precipitation in C-Z bulk silicon.

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.

Novel dielectric/silicon planar structures formed by ion beam synthesis

Abstract Multilayer SiO 2 Si planar structures with abrupt interfaces have been formed in single crystal silicon by ion beam synthesis, using multiple energy implants and high temperature annealing. SIMS, RBS and cross-section TEM techniques have been used to follow the evolution of these structures. Provided an implantation sequence from high to low energy is followed, the synthesised buried SiO 2 layers do not interact during the implantation, and the Si and SiO 2 thicknesses are independently defined by the ion energy and dose, respectively. The formation, during high temperature annealing, of planar structures with abrupt interfaces, is driven by chemical forces, which cause the excess oxygen in the supersaturated silicon matrix to segregate at the peaks of the oxygen concentration profiles. The mechanism is qualitatively similar to diffusion controlled precipitate growth in bulk silicon.

Buried layers of silicon oxy-nitride fabricated using ion beam synthesis

Abstract Ion beam synthesis (IBS) has been used to fabricate buried compound layers in silicon. These layers were produced by implanting combinations of O + and N + ions or NO + ions at 200 keV/atom into 100 single crystal silicon maintainted at a temperature of between 510°C and 580°C. The specimens were then annealed at 1200°C for two hours. It is found that the types of structure formed are highly dependent on the sequence in which the ions are implanted. When oxygen is implanted prior to nitrogen, the nitrogen segregates to the wings of the oxygen distribution where it forms an oxy-nitride. The presence of nitrogen, during the subsequent anneal is found to improve both the crystalline quality of the silicon overlayer and to reduce the impurity concentration therein. A similar improvement in the crystallinity of the silicon overlayer is also observed when oxygen and nitrogen are implanted together as NO + . Conversely if nitrogen is implanted prior to oxygen the redistribution of the impurities, during annealing, leads to a degradation in the structure, when compared to a specimen only implanted with oxygen. In this case the portion of the silicon overlayer adjacent to the buried layer, is highly defective with a high impurity concentration. Models based upon self diffusion and impurity interactions within the matrix are advanced to describe the evolution of the buried structures.

Activation energy for fluorine transport in amorphous silicon

The transport of ion implanted F in amorphous Si is studied using secondary ion mass spectroscopy and transmission electron microscopy. Significant redistribution of F is observed at temperatures in the range 600°C to 700°C. The measured F depth-profiles are modelled using a simple Gaussian solution to the diffusion equation, and the diffusion coefficient is deduced at each temperature. An activation energy of 2.2eV±0.4eV for F transport is extracted from an Arrhenius plot of the diffusion coefficients. It is shown that the F transport is influenced by implantation induced defects.

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.