Oxygen Precipitation In Silicon Research Articles

Small angle X-ray scattering study of oxygen precipitation in silicon

Czochralski-grown dislocation-free silicon is used in the semiconductor industry almost exclusively for manufacturing VLSI devices. Such material contains small quantities (∼20 ppm) of dissolved oxygen, which can have a crucial effect on the properties of produced devices. Therefore it is of great importance to study its precipitation in a silicon matrix after given thermal treatment. The small angle X-ray scattering (SAXS) technique was used to study oxygen precipitation in monocrystalline silicon samples. We used 8 and 16 keV radiation to overcome the high absorption at low energies. A series of samples has been prepared with controlled sequence of oxygen nucleation and precipitation phase and measured with SAXS. It is shown that this low contrast changes in standard wafers can be investigated using synchrotron radiation.

Oxygen Precipitation in Silicon Doped with Tin

Oxygen Precipitation in Silicon Doped with Tin

Strain-induced transformation of amorphous spherical precipitates into platelets: Application to oxide particles in silicon

The spherical shape of an amorphous precipitate becomes unstable if the combination P2R of precipitate radius R and pressure P exceeds some critical value. This critical value was found to be about 4.44 Gσ, where G is the matrix shear modulus and σ is the specific energy of the precipitate/matrix interface. Once this instability criterion is fulfilled, the initially spherical particle will reduce the total free energy (the sum of strain energy and the surface energy) by becoming a thin oblate spheroid (effectively, a platelet). The actual pressure P in the course of oxygen precipitation in silicon is controlled by a high self-interstitial supersaturation caused by emission of self-interstitials by growing precipitates. The duration of annealing necessary to reach the stage of collapse of spheres into platelets is calculated as a function of temperature and the precipitate density. Calculated results are compatible with the experimentally observed annealing conditions for platelet formation. Another important example of sphere to platelet transformation is microdefect formation in vacancy-type silicon. In this case a large negative value of P is sufficient to induce collapse.

Enhanced oxygen precipitation in silicon due to grown-in spatial inhomogeneities in the oxygen distribution

Fine control of oxygen precipitation during annealing of silicon wafers is required for modern microelectronics processing. We show that the presence of microscopic spatial inhomogeneities in the oxygen concentration caused by fluctuations during crystal growth, can lead to significantly enhanced effective nucleation rates. This effect is demonstrated for a simple nonlinear reaction-diffusion model and then confirmed by simulations of oxide precipitation.

Coupled-flux nucleation modeling of oxygen precipitation in silicon

Experimental data for oxygen precipitation densities in Czochralski-grown silicon following multistep annealing treatments are compared with predictions from a coupled-flux model for time-dependent nucleation. This is a more correct model for diffusion-controlled nucleation processes than is the classical theory of nucleation since it directly couples the two stochastic fluxes of interfacial attachment and long-range diffusion. Quantitative agreement is obtained between the measured and calculated densities for nucleation temperatures greater than 650 °C. Good agreement is obtained for lower temperatures if the oxygen diffusion rate is taken to be larger than is predicted from high-temperature diffusion data. The fit values for the diffusion coefficient from the nucleation data are in good agreement with recent results from dislocation-unlocking experiments. The oxygen loss calculated by coupled-flux nucleation and diffusion-limited growth agrees with the experimental observations. Classical theory nucleation calculations predict a much greater oxygen loss, signaling the failure of the theory to correctly treat nucleation when long-range diffusion is important, true in most solid-state precipitation processes.

Early stages of oxygen precipitation in silicon: The effect of hydrogen

The formation of small oxygen clusters upon heat treatment at 280–375°C was studied in crystalline silicon doped with hydrogen by high-temperature in-diffusion. The presence of hydrogen in concentrations of 1015–1016 cm−3 significantly enhances (by up to a factor of 106 at T≤300°C) the oxygen diffusivity in Si crystals. Possible mechanisms of interaction between O and H impurity atoms and the origin of hydrogen-enhanced oxygen diffusion in silicon are discussed.

Simulation of oxygen precipitation in silicon

A theoretical model for nonuniform bulk precipitation is suggested. It can be used for describing internal gettering and providing better insight into SOI-related processes. Oxygen precipitation is shown to be a diffusion-limited process. The size of oxygen precipitates as a function of temperature and annealing time, as well as the thickness of a defect-free zone at the surface, were determined. A test for the optimization of SOI layers resulted from postimplantation annealing is suggested.

Spatially inhomogeneous oxygen precipitation in silicon

A theoretical model for point-defect precipitation in crystals, which is a generalization of the well-know Ham model, has been proposed. The equations obtained are helpful in describing the kinetics of oxygen precipitation in silicon, and in determining the kinetics of variation of the mean geometrical dimensions of clusters. A theoretical model of spatially inhomogeneous precipitation has been developed. This model can be used to describe processes of internal gettering and creation of insulating layers in silicon.

Oxygen precipitation in silicon: Experimental studies and theoretical investigations within the classical theory of nucleation

Quantitative measurements of the oxygen precipitate rate as a function of annealing were made in Czochralski-grown silicon wafers that contained different initial concentrations of oxygen. All wafers were annealed at 1000 °C for 15 min to ensure that the initial cluster-size distributions were identical in all samples of the same composition prior to the multi-step annealing treatments used for the precipitation studies. The experimental data are compared with numerical predictions for time-dependent nucleation within the classical theory of nucleation. Quantitative agreement is obtained between the measured and calculated densities of oxygen precipitates for nucleation temperatures greater than 600 °C, but only over a narrow range of oxygen composition. Below 600 °C, the measured density for all samples is orders of magnitude larger than is predicted from the model. Further, the measured data show an anomalously small temperature dependence for the induction time for nucleation that does not scale with the diffusion coefficient, as expected from the classical theory of nucleation. Fundamentally, the classical theory of nucleation cannot explain the time-dependent nucleation of oxygen precipitates for temperatures below 650 °C. A possible reason is given.

Luminescence Properties of Oxygen-Containing Silicon Annealed at Enhanced Argon Pressure

The effect of annealing at argon pressure, HP, up to 1.5 GPa on photoluminescence, PL, of oxygen-containing silicon (of Czochralski grown, Cz-Si, and of oxygen-implanted, Si:O) and of thermally — grown SiO2 films was investigated. Pressure-annealing of Cz-Si and Si:O at 720 to 1400 K affects the intensity of dislocation-related PL lines in the infrared, which follows from HP effect on oxygen precipitation in silicon and Si:O. For the first time visible/ultraviolet PL of the SiO2 surface film was detected after subjecting it to pressure treatment at (1400 to 1550) K, (0.9 to 1.5) GPa.

Early Stages of Oxygen Precipitation in Silicon, R. Jones (ed.)

Early Stages of Oxygen Precipitation in Silicon, R. Jones (ed.)

Diffusion and Precipitation of Oxygen in Silicon Doped with Germanium

Diffusion and Precipitation of Oxygen in Silicon Doped with Germanium

Diffusion and Precipitation of Oxygen in Silicon Doped with Germanium

Diffusion and Precipitation of Oxygen in Silicon Doped with Germanium

Initial Stage of Oxygen Precipitation in Silicon

Initial Stage of Oxygen Precipitation in Silicon

Spatial variations in oxygen precipitation in silicon after high temperature rapid thermal annealing

Spatial variations of oxygen precipitation have been studied in silicon wafers submitted to rapid thermal annealing (RTA) in nitrogen ambients at a temperature above 1150 °C prior to a two-step precipitation treatment. The samples submitted to high temperature preannealing show a consistent enhancement of oxygen precipitation, which is dependent on the RTA time and temperature. Oxygen precipitate density measurements show that oxygen precipitation is not homogeneous inside the wafer, but peaks near the surfaces, with a minimum in the bulk. The high treatment in N2 results in the formation of defects which act as precursors for the subsequent nucleation and growth of oxygen precipitates. There is strong evidence that these precursors are generated by the thermal nitridation of the silicon surface and subsequent vacancy injection into the bulk of the wafer.

Kinetic Model of Thermal Donor Evolution

ABSTRACTKinetic aspects of thermal donor (TD) formation in Czochralski silicon are shown to be consistent with the evolution of small oxygen clusters, as described within the classical theory of nucleation. Predictions for TD generation and interstitial oxygen loss are presented. Favorable agreement with experimental data requires that the rate constants describing cluster evolution be increased over those expected for a oliffusion-limited flux based on a normal diffusion coefficient for oxygen in silicon. This may signal an anomalously high diffusion rate for temperatures less than 500°C, as has been suggested by others. However, it may instead signal an enhanced concentration of free oxygen near clusters smaller than the critical size for nucleation. This is expected when the interfacial attachment rates become comparable with the rates at which oxygen atoms arrive in the vicinity of the sub-critical clusters. The link between thermal donor generation and oxygen precipitation processes demonstrated here provides a consistent framework for better understanding and controlling oxygen precipitation in silicon. Further, the kinetic TD generation and oxygen loss data provide a new window into the dynamical processes for small clusters, which underlie all nucleation phenomena.

A model for oxygen precipitation in silicon including bulk stacking fault growth

This paper describes a model that simulates the precipitation kinetics of oxygen and the evolution of the precipitate density in annealed Czochralski-silicon wafers. A discrete rate equation representation combined with Fokker-Planck equations are used to treat precipitation of oxygen and simultaneous formation of bulk stacking faults. This approach allows one to describe both statistical clustering during nucleation and diffusional transport during growth. The model considers explicitly influences of self interstitials and stress on precipitation of oxygen and thus is able to accurately predict the experimental observations published previously. In particular, we compare simulation results of precipitated oxygen concentration in 2-step, 3-step, complementary metal oxide semiconductor type multi-step, and rapid thermal anneals with experimental results taken from the literature and discuss them.

Diffusion limited oxygen precipitation in silicon: Precipitate growth kinetics and phase formation

Published experimental data on silicon oxide precipitate growth kinetics are interpreted in the framework of the theory of Ham for diffusion limited precipitation. A growth law for plate-like, octahedral and spherical precipitates is derived showing a size dependence which varies as the square root of time. Using well accepted data for the solubility and the diffusion constant of oxygen in silicon, the calculations suggest that the precipitated phase is closer to SiO than to SiO2.

Impact of oxygen related extended defects on silicon diode characteristics

The electrical activity of extended lattice defects formed by interstitial oxygen precipitation in silicon is studied. Their impact on diode characteristics and on minority carrier lifetime is addressed for different initial oxygen contents and pretreatments. The carrier traps present in the substrate are studied with deep level transient spectroscopy and with photoluminescence spectroscopy. The obtained electrical results are correlated with those of structural and chemical characterization using cross-section transmission electron microscopy and Fourier transform infrared spectroscopy.

Model of partitioning of point defect species during precipitation of a misfitting compound in Czochralski silicon

The partitioning of point defect species during diffusion controlled precipitation of a misfitting compound in Czochralski silicon is studied using the principle of maximum degradation rate of the total system free energy. The degradation rate of the system free energy is obtained from the entropy production due to mass diffusion in the matrix. The results are then compared with those obtained using the principle of maximum growth rate. It is shown that, for a precipitation process involving more than one chemical or structural component species with their concentrations deviating from the appropriate thermal equilibrium values, the maximum growth rate description does not generally correspond to that of the maximum degradation rate of the system free energy. The results are then applied to oxygen precipitation in silicon, showing some equilibrium characteristics pertinent to a multicomponent system with intrinsic point defects acting as pseudocomponents. It is also shown that, depending on the intrinsic point defect concentrations at the far field of diffusion, the oxide precipitate can grow either by emitting or by absorbing both vacancies and Si self-interstitials.