High temperature oxygen implantation in silicon: Soil structure formation characteristics

doi:10.1016/S0168-583X(87)80060-5

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volumes 19–20, Part 1, 1987, Pages 294-298

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It has recently been shown that a high quality silicon-on-insulator (SOI) system may be obtained via high dose implantation of oxygen followed by an appropriate high temperature annealing. This technique appears to be a potentially powerful tool for VLSI technology applications. In the present paper we describe a study of the SOI system formation in an attempt to correlate its physical characteristics to the substrate temperature during oxygen implantation and to the high temperature annealing parameters. In order to form a buried SiO₂ layer, single-crystal, n-type, (100) Si wafers were implanted with 1.4 × 10¹⁸ /cm², 150 keV O ⁺ ions at temperatures in the range 450–750°C and subsequently annealed at temperatures between 1200 and 1300°C. The annealed samples were characterized using Rutherford backscattering (RBS)/channeling measurements, Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and cross-sectional transmission electron microscopy (TEM) analysis. The results confirm our previously reported experimental evidence showing that minimum residual damage for the “as implanted” state of the Si surface layer can be observed for an implantation temperature in the range 600–650°C. During the subsequent high temperature annealing most of the implanted oxygen is progressively removed from the Si surface layer by dissolution of the SiO₂ precipitates, followed by oxygen diffusion and trapping in the buried oxide layer. The resulting oxygen contamination of the Si surface layer drops below 10¹⁹ at./cm³ after a 2 h-annealing at 1300°C. During a further annealing the spatial rearrangement of the SOI structure occurs, leading to an improvement in the quality of the Si/SiO₂ interface and a decrease in the density and size of the SiO₂ precipitates. The residual oxygen concentration in the Si surface layer appears, however, to be related to the morphology of the SOI system in the “as implanted” state, and thus to the substrate temperature during implantation.

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Cited by (22)

RBS, RHEED and THEED studies of SIMOX and SIMNI structures formed by ion beam synthesis
1993, Vacuum
Although the field of ion beam synthesis of buried dielectric layers in silicon received much attention in the 1980s, specific details of the process still remain that need to be clarified and reconsidered in order to utilize the technique to its fullest advantage. This research attempts (i) to outline the implantation conditions that minimize the damage in the silicon surface layer of substrates incorporating buried layers of either SiO₂ or Si₃N₄, and (ii) to explore the possibility of directly creating buried layers of Si₃N₄. In order to have useful single crystal silicon on the top of the buried layer, it is necessary to conduct implants at elevated substrate temperatures and to employ sample preheating from an external heat source independent of the ion beam. The use of high intensity nitrogen implantation looks like a promising approach which enables the synthesis of continuous layers of stoichiometric Si₃N₄ in situ. Combined analysis methods including RBS, RHEED and THEED are used to characterize the resulting as-implanted structures.
Concentration profiles of high dose MeV oxygen implanted silicon
1993, Nuclear Inst. and Methods in Physics Research, B
We have investigated the concentration profiles of n-type Si wafers implanted with 6 MeV oxygen ions at 2 μA⁻² to doses of 3 × 10¹⁷ and 10¹⁸ cm⁻², and 1 MeV ions at 10 μA cm⁻². Both the as-implanted and annealed samples have been characterized by secondary ion mass spectrometry. For the as-implanted samples, the O distribution is far from Gaussian, and the peak of the distribution shifts to greater depth as the dose increases. This shift is due to two effects: swelling of the silicon in the region of the peak, due to the formation of oxide, and reduction of the stopping power of the material in the region in which large numbers of vacancies are produced. In the 6 MeV as-implanted samples we have also observed a small peak in the concentration of O at ≈ 2 μm, roughly half of the projected range of the incident ions. We attribute this peak to precipitation of O at the depth at which large numbers of vacancies are produced but where the vacancy and interstitial peaks do not overlap. This peak disappears after annealing, and is not observed in the 1 MeV samples. We attribute this latter effect to heating produced by high implantation current in this case. After annealing, oxygen is segregated at the surface and near the peak of the initial distribution. This peak tends to become rectangular, and saturates in the 10¹⁸ cm⁻² samples, indicating the formation of a stoichiometric SiO₂ layer. However, a band of oxide precipitates is observed at slightly lesser depth. In addition there are silicon inclusion in the oxide, near both interfaces.
Synthesis of buried insulating layers in silicon by ion implantation
1992, Materials Chemistry and Physics
The effect of dose and temperature on the as-implanted microstructure of oxygen-implanted silicon
1992, Materials Science and Engineering B
The effect of implantation temperature and oxygen dose on the structure of as-implanted separation by implantation of oxygen (SIMOX) wafers was studied by means of Rutherford backscattering spectrometry and ion channelling, secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Silicon wafers were implanted with 400 keV ³²O₂⁺ ions at implantation temperatures varying from 200 °C to 700 °C, with oxygen doses from 5 × 10¹⁶ O⁺ cm⁻² to 1.4 × 10¹⁸ O⁺ cm⁻². The formation of an amorphous phase in the buried layer, the crystallinity of the silicon overlayer and the corresponding layer thicknesses were monitored. A critical dose for the formation of an amorphous layer was established as a function of implantation temperature $T_{i}$ . The influence of $T_{i}$ on the microstructure was examined for a constant dose. The damage in the buried layer and the damage in the silicon overlayer relate to the implanted dose and the implantation temperature in a complex way.
Self-annealing in ion-implanted Si and GaAs
1991, Vacuum
Oxygen-redistribution process in SIMOX
1989, Nuclear Inst. and Methods in Physics Research, B
Silicon-on-insulator structures were formed by high dose (1.2 × 10¹⁸ O⁺/cm²) oxygen implantation at 150 keV. The oxygen-redistribution processes during post-implantation annealing at 1280°C for periods of from 5 min to 12 h were examined by cross sectional transmission electron microscopy and X-ray photoelectron spectroscopy.
During the heating-up process, the small polyhedral oxide precipitates which are present in the vicinity of the buried oxide layer at around 1150 °C become rounded off and grow larger through coalescence above 1230°C.
Coalesced oxide-precipitates form an irregular Si/SiO₂ interface and a portion of them melt into the buried oxide layer at the initial stage of the isothermal annealing at 1280°C. However, most of them disappear during further annealing. As a result, an abrupt Si/SiO₂ interface is formed.
On the basis of these results, we discuss the correlation between the coalescence process and the dissolution process of the oxide-precipitates and its effect on the final thickness of the buried oxide layer.

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High temperature oxygen implantation in silicon: Soil structure formation characteristics

Vacuum

Thin Solid Films

Nucl. Instr. and Meth.

Appl. Phys. Lett.

Jpn. J. Appl. Phys.

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J. Appl. Phys.