Oxygen Precipitation In Silicon Research Articles

Formation of Oxygen-Containing Centers in Irradiated Silicon Crystals during Annealing in the Temperature Range of 450–700°С

The processes associated with transformations of oxygen-related radiation-induced defects in Czochralski-grown silicon crystals irradiated with fast electrons or neutrons and subjected to heat-treatment in the temperature range of 450–700°C have been studied by means of IR absorption spectroscopy. It is found that, upon disappearance of the VO3 and VO4 defects, new vacancy-oxygen-related complexes, which give rise to a number of vibrational absorption bands in the wavenumber range of 980–1115 cm–1, are formed. It is argued that these complexes are radiation-induced VOm centers (m ≥ 5), which serve as nucleation centers of enhanced oxygen precipitation in silicon.

The effects of pre-annealing on oxygen precipitation in silicon P/P-epitaxial wafers

Abstract Herein, the effect of pre-annealing on oxygen precipitation in a silicon P/P-epitaxial wafer was investigated using an experimental approach. Czochralski-grown silicon wafers were annealed at 800–900 °C to enhance their bulk micro defects (BMDs), before the epitaxial growth process. The effect of the pre-annealing temperature on oxygen precipitation was greater than that of the pre-annealing time, and the effect of pre-annealing temperature varied between polished and epitaxial wafers. Regarding pre-annealed epitaxial wafers that were annealed at low temperatures, the pre-annealing time also had as large an effect on BMD formation as the pre-annealing temperature. These experimental results were used to determine the optimal pre-annealing temperature for enhancing oxygen precipitation in epitaxial wafers. The experimental results regarding the optimal conditions were consistent with prior hypotheses. Crystal originated particles (COPs) and COP-free crystals exhibited their highest BMD density values at similar pre-annealing temperatures.

Impact of iron on the room temperature luminescence efficiency of oxygen-containing precipitates in silicon

Oxygen precipitation in silicon has been associated with a weak room temperature sub-bandgap luminescence emission at around 1600 nm. We show that the additional presence of iron impurities enhances this emission by an order of magnitude and results in a red shift of the peak luminescence by approximately 45 nm. We not only observe an increase in the luminescence emission with iron contamination level but also with the density and size of the oxide precipitates. Moreover, we provide evidence that the sub-bandgap luminescence emission increases proportionally with the concentration of iron segregated to oxide precipitates after high temperature (>700 °C) annealing and thus allows evaluation of the gettering efficiency of oxygen-containing precipitates. Annealing of iron-contaminated samples at low temperatures (550 °C) results in a considerable reduction in the interstitial iron concentration without changing the sub-bandgap luminescence, indicating that the sink to which iron diffuses depends upon temperature.

シリコン中の酸素の析出現象 : III. プロセス誘起不純物偏析

シリコン中の酸素の析出現象 : III. プロセス誘起不純物偏析

Strain relief via silicon self-interstitial emission in highly boron-doped silicon: A diffuse X-ray scattering study of oxygen precipitation

Oxygen precipitation in highly boron-doped Czochralski silicon (5 mΩ cm resistivity) was studied, and a strain-relieving mechanism involving the emission of silicon interstitial atoms (ISi) was identified. Strain-sensitive X-ray diffraction was employed, and through a comparison with complementary electron microscopy measurements a linear misfit strain ϵ=0.01 was determined. Different behavior concerning strain relaxation was measured for wafer-type samples (760 μm thickness) and thick samples (2 mm thickness), which was explained with out-diffusion of ISi in the thinner samples. Based on the experimental findings, a model was developed which invokes an increase in the solubility of interstitial silicon atoms upon boron doping. The model successfully accounts for different effects of boron doping on oxygen precipitation in silicon, which were reported on in literature such as preferential octahedral morphology of precipitates, enhanced nucleation, and relaxed accommodation of the precipitates with respect...

(Invited) Modeling of Oxygen Precipitation in Silicon

A model for the precipitation of oxygen and associated dislocation loops in Czochralski-grown silicon is presented. Beginning with kinetic rate equations describing the growth and dissolution of oxide precipitates, a reduced model based on the moments of the precipitate size distribution is developed and validated against experimental data. Comparisons with the full, rate equation-based model show that the reduced version is comparably accurate while requiring significantly less computational power. The formation of dislocation loops due to silicon interstitial ejection during precipitate growth is modeled using a simple, moment-based approach.

Invited; Modeling of Oxygen Precipitation in Silicon

A model for the precipitation of oxygen and associated dislocation loops in Czochralski-grown silicon will be presented. Beginning with kinetic rate equations describing the growth and dissolution of oxide precipitates, a reduced model based on the moments of the precipitate size distribution is developed and validated against experimental data. Comparisons with the full, rate equation-based model show that the reduced version is comparably accurate while requiring significantly less computational power. The formation of dislocation loops due to silicon interstitial ejection during precipitate growth is modeled using a simple, moment-based approach.

Simulation of spatially-heterogeneous oxygen precipitation in silicon with allowance for internal mechanical stresses

A new model of the kinetics of oxygen precipitation in silicon, which allows for the effect of internal mechanical stresses that arise at the boundaries of precipitation particles on the speed of oxygen transport and silicon oxidation reactions, is developed based on an approach previously proposed by authors. Temporal variations of the spatial distribution of oxygen in a silicon plate are calculated under conditions of the formation of precipitation particles. Dependences of the width of a defect-free zone formed in a plate on the time and temperature of the annealing are obtained. This is an important characteristic of the formation of an internal getter in carriers. The allowance for internal mechanical stresses is shown to result in decreasing the rate of the widening of a defect-free zone, which agrees with the experiment data. The results can be used to optimize the formation of an internal getter.

A reduced moment-based model for oxygen precipitation in silicon

A model for the precipitation of oxygen and associated dislocation loops in Czochralski-grown silicon is presented. Beginning with kinetic rate equations describing the growth and dissolution of oxide precipitates, a reduced model based on the moments of the precipitate size distribution is developed and validated against experimental data. The complete model source code is provided. Comparisons with the full, rate equation-based model show that the reduced version is comparably accurate, while requiring significantly less computational power. The formation of dislocation loops due to silicon interstitial ejection during precipitate growth is modeled using a simple, moment-based approach. An analysis of the sensitivity of the oxygen model to parameters is included.

X‐ray in situ observation of oxygen precipitation in silicon confirmed with ex situ detection methods

AbstractA focusing Laue diffractometer is used to analyze the strain field in silicon. The source for this so called strain field diffraction (SFD) setup is a high energy X‐ray tube. In the present work this setup is used to monitor the strain generated by growing oxygen precipitates (Bulk Micro Defects, BMDs) in situ at temperatures up to 1000 °C. By choosing appropriate thermal treatments a correlation of the SFD signal with BMD parameters gained with conventional analytic techniques (FT‐IR, infra red light scattering, TEM) is established. From this, the detection limit of the SFD setup for BMDs is determined at a diameter of 7 nm and a density of 1013 cm−3. This range is only covered by TEM so far. Further, the diffracted intensity provides a measure for the level of precipitation occurred.

Effect of vacancies on oxygen precipitation in germanium-doped Czochralski silicon

The effect of vacancies introduced by rapid thermal annealing (RTA) on the oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. GCZ silicon is annealed at 650–1050 °C to facilitate the precipitation of oxygen. It is observed that the oxygen precipitation in silicon is enhanced by both the vacancies introduced during RTA pretreatment and the doping of germanium. Especially, we find that the enhancement effect of vacancies on the precipitation of oxygen is larger than that of germanium atoms. In contrast to non-RTA pretreatments, RTA pretreatments lead to less significant oxygen precipitation in GCZ silicon than in conventional Czochralski (CZ) silicon at temperatures ranging from 850 to 950 °C. The mechanism for the interaction between vacancies and germanium atoms in CZ silicon is elucidated.

XBIC/μ-XRF/μ-XAS analysis of metals precipitation in block-cast solar silicon

The results of the investigations of the interaction between the different impurities in intentionally contaminated block-cast multi-crystalline silicon by means of synchrotron-based microprobe techniques XBIC (X-ray beam induced current), μ-XRF (X-ray fluorescence microscopy) and μ-XAS (X-ray absorption microspectroscopy) recently implemented at beamlines ID-21 and ID-22 of ESRF, Grenoble, are presented. It was found that Si 3N 4/SiC particles frequently observed in the upper part of multi-crystalline Si blocks represent effective sinks for Fe and Cu impurities. The amount of precipitated iron was the same order magnitude both at nitride and carbide particles. The amount of Cu precipitated at the SiC inclusions was significantly larger than that at Si 3N 4 rods. Chemical state of the copper precipitates was identified as copper-rich silicide Cu 3Si. The anneal at 950 °C that is known to enhance oxygen precipitation in silicon was found to accompany with the enhanced formation of nanoscale iron disilicide precipitates both inside the grains and at grain boundaries.

<i>In Situ</i> Observation of Oxygen Precipitation in Silicon with High Energy X-Rays

Oxygen precipitation in silicon has been studied in-situ by high energy X-ray diffraction. A gain of diffracted intensity is expected if an ideal crystal is distorted by growing precipitates as the diffraction mode changes from a dynamical to a more kinematical one. Irreversible changes in the intensity of a 220 and a 400 Bragg peak are detected for Czochralski grown samples only, but not in a float zone grown reference crystal. Thus, these changes are attributed to oxygen precipitation, which is confirmed by a subsequent classical ex-situ characterization. Further, the changes of the intensities of the two measured Bragg peaks are compared to each other to get the level of change in the diffraction mode from a dynamical to a kinematical one. The detection limit of the specific setup is estimated via a simulation of the defect inventory to correspond to a precipitate diameter of 50nm with the density of 6.9•109 1/cm3. The diffraction experiments are done with polychromatic and divergent X-rays generated by a laboratory source, albeit with high energy. This results in a simple and accessible setup for the characterization of oxygen precipitates.

Enhanced oxygen precipitation in neutron-irradiated nitrogen-doped Czochralski silicon crystal

Nitrogen and vacancies were intentionally introduced into Czochralski silicon crystal by doping and neutron irradiation, respectively, to study the effect on oxygen precipitation. A series of isochronal anneals in the temperature range of 700–1150 °C revealed that vacancies showed the prominent enhancement effect on oxygen precipitation at temperatures below 1000 °C, whereas nitrogen exhibited the evident enhancement in oxygen precipitation at temperatures above 900 °C. It is suggested that the vacancies induced by neutron irradiation form VnOm (n, m≥1) complexes acting as nuclei to facilitate oxygen precipitation in silicon. However, the VnOm complexes are not stable at higher temperatures; thus, the enhancement effect of vacancies on oxygen precipitation decreases evidently as the temperature increases above 1000 °C. In addition to the formation of new nuclei based on the VnOm complexes, the growth of grown-in oxygen precipitates is also facilitated by the incorporation of high concentration vacancies in the neutron-irradiated silicon. In nitrogen-doped silicon, the enhanced oxygen precipitation at high temperatures primarily depends on nitrogen concentration rather than vacancy concentration as a result of forming stable N2V2 complexes acting as precipitate nuclei.

Effect of transition metals on oxygen precipitation in silicon

Effects of iron and copper impurities on the amount of precipitated oxygen and the oxide precipitate and stacking fault densities in Czochralski-grown silicon have been studied under varying thermal anneals. Silicon wafers were intentionally contaminated with iron or copper and subsequently subjected to different two-step heat treatments to induce oxygen precipitation. The iron contamination level was 2 × 1013 cm-3 and copper contamination level 6 × 1013 cm-3. Experiments did not show that iron contamination would have any effect on the amount of precipitated oxygen or the defect densities. Copper contamination tests showed some indication of enhanced oxygen precipitation.

Oxygen Precipitation of Nitrogen-Doped Czochralski Silicon Subjected to Multi-Step Thermal Process

The effect of nitrogen on oxygen precipitation in nitrogen- doped Czochralski (NCZ) silicon subjected to the simulated CMOS process was investigated. It was found that nitrogen could enhance oxygen precipitation in silicon during the multi- step thermal process. And the denuded zone in NCZ silicon was formed near the surface, through it was not as wide as that in conventional Czochralski (CZ) silicon. It was also found that the loss rates of oxygen concentration in the NCZ silicon pre- annealed by rapid thermal process (RTP) were higher than those in the CZ silicon. In addition, during the multi-step process the oxygen concentrations in the CZ silicon and NCZ silicon after the multi-step pre-annealing, which could create denuded zone, changed slightly.

Control of Oxygen Precipitation in Silicon by Infrared Laser Irradiation

We have investigated the effect of infrared laser irradiation on the oxygen precipitation in silicon crystals during the heat-treatments. The laser light of the wave numbers of 1085 cm-1 was adopted, which is close to the wave number of the infrared absorption by oxygen in silicon (Si-O-Si) at high temperature. We have found that for the high-temperature anneals around 1200 °C for 1-2 h, the infrared laser irradiation during the anneals significantly (almost completely) suppresses the oxygen precipitation.

Critical precipitate size revisited and implications for oxygen precipitation in silicon

A generalized expression is derived describing the impact of intrinsic point defects and strain on the critical size of spheroidal incoherent precipitates. An important phenomenon that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical precipitate size, on the amount of emitted intrinsic point defects, and on the precipitated phase itself. The theoretical results are illustrated for the case of oxygen precipitation in silicon.

Precipitation and extended defect formation in silicon

The impact of self-interstitials and strain on the critical size for nucleation of incoherent precipitates is well-known. A factor that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical r size and on the precipitated phase. The theoretical results are illustrated for the case of oxygen precipitation in silicon. The growing precipitate can also cause the nucleation of extended lattice defects such as dislocations and stacking faults in the surrounding matrix. A model is presented to predict stacking fault r nucleation.

Diffusion–influenced nucleation: a case study of oxygen precipitation in silicon

The classical theory of homogeneous nucleation is an interface–limited theory and does not strictly apply for transformations where long–range diffusion is dominant. A new approach that takes account of the coupled stochastic fluxes of interface attachment and long–range diffusion is presented. Steady–state nucleation rates can be orders of magnitude smaller and the induction times for time–dependent nucleation correspondingly larger than expected from the classical theory. In solute precipitation, the regions of the parent phase near subcritical precipitate clusters are enriched (rather than depleted) in solute. Oxygen precipitation in silicon is chosen to illustrate these features. Measured precipitate densities following multi–step anneals show better agreement with predictions from the coupled–flux model than with those from the classical theory. The kinetics of formation for small oxide clusters and the dependence of their population density on the initial oxygen concentration agree well with data for thermal donor defects.