Interstitial Oxygen Concentration Research Articles

Czochralski silicon characterization by using thermoelectric power measurements at high pressure

The thermoelectric power of Czochralski silicon with various interstitial oxygen contents has been investigated at high pressure up to 16GPa by using automated set up and synthetic diamond anvil cell. The values of semiconductor–metal transition pressure established from thermoelectric power on pressure dependencies are correlated with mechanical properties (microhardness) and oxygen content. The possibilities of application of the properties studied for Czochralski silicon testing are discussed.

Deep Levels in High-Temperature 1 MeV Electron-Irradiated n-Type Czochralski Silicon

This work describes the radiation defects formed in high-temperature (450°C) 1 MeV electron-irradiated n-type Czochralski (Cz) silicon. A dedicated irradiation configuration has been used, which relies on sample heating by the energy deposited by the electron beam current. It is shown that the vacancy oxygen (VO) or A center is the dominant radiation defect under these circumstances. In addition, a whole series of unknown deep electron traps is reported, whose trap parameters (activation energy, electron capture cross section) depend, among other factors, on the starting interstitial oxygen concentration. It is speculated that their origin is related to complexes of oxygen and vacancies.

Radiation-induced junction formation behavior of boron-doped Czochralski and float zone silicon crystals under 3 MeV proton irradiation

A comparative study was performed on the junction formation behavior of boron-doped p-type Czochralski (Cz) and float zone (Fz) Si wafers, which differed mainly in interstitial oxygen concentration, upon 3 MeV proton irradiation with fluences of up to 2×1015 cm−2. The region around the projected range in both the Cz and Fz Si wafers converted its conduction type to n type at fluences between 1×1013 and 3×1013 cm−2, which is most probably due to the formation of hydrogen-related donors. The main difference between the Cz and Fz Si wafers was in the susceptibility of the proton track region to type conversion. The proton track region of the Cz Si wafer converted to n type at fluence between 1×1013 and 3×1013 cm−2, whereas that of the Fz Si wafer showed only an increase in resistivity without any type conversion as the fluence increased up to 2×1015 cm−2, which was attributed to oxygen-related donor formation in the case of the Cz Si wafer. The present results are discussed with respect to the radiation-induced failure mechanisms of n+/p/p+-structured Si space solar cells based on boron-doped Cz and Fz Si.

Radiation defects in neutron irradiated silicon with high oxygen concentration

In silicon material with oxygen concentration in the range (4–9)×1017cm−3, grown by the CZ method and irradiated by reactor neutrons, the interstitial oxygen mainly participates in A-center (V+O) creation. A-center concentration is linearly dependent on neutron fluence up to Φ=1018n/cm2, value at which saturation occurs caused not by the exhaustion of dissolved oxygen but rather by vacancy-interstitial atom annihilation competitive mechanisms. A-center annealing (T>300°C) does not lead to the full restoring of interstitial oxygen concentration. Repeating neutron irradiation and annealing causes a decrease of oxygen complex activity and the silicon behaves as a low-oxygen material.

Effects of grain boundary on impurity gettering and oxygen precipitation in polycrystalline sheet silicon

The effects of grain boundaries (GB) in polycrystalline sheet silicon on impurity gettering and oxygen precipitation were investigated by electron beam induced current (EBIC), deep level transient spectroscopy (DLTS), micro-Fourier-transform infrared spectroscopy (FTIR), and preferential etching/Normaski optical microscopy techniques. Both as-grown and thermally processed wafers were studied. A correlation between GB density and transition metal concentration was quantitatively established by combining DLTS and EBIC studies. It was found that four deep levels arising from Fe–B, Fe–Al, Cr–B, and Fei were present in the as-grown sample, and their concentrations decrease with increasing GB density. GB gettering was further verified by the presence of an EBIC image contrast halo around the GB. Preferential etching also revealed a precipitate density of 2×107 cm−2 on the GB. After processing, a clearly defined oxygen precipitate denuded zone formed around the GB with the interstitial oxygen concentration [Oi] decreased from 14.4 to 2.2×1017 cm−3. Micro-FTIR showed that, for both processed and as-grown samples, more silicon oxynitride appears in the GB than in the intragrain region. Since nitrogen enhances oxygen precipitation, it is likely that nitrogen preferentially precipitated on the GB during the wafer formation process and resulted in a nitrogen depletion zone, where oxygen precipitation was further suppressed and a denuded zone formed.

Characterisation of oxygen and oxygen-related defects in highly- and lowly-doped silicon

In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C– V) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).

Physical, biological and chemical processes during storage and spontaneous combustion of waste fuel

The storage of unsorted industrial waste (IND) fuel and refused-derived fuel (RDF) in piles at two different locations in Sweden was investigated. The objective was to assess the feasibility of waste storage in open areas for later energy utilization, and to study the physical, biological and chemical processes that occur during storage, by monitoring a number of parameters. One monitored IND pile showed an increase in temperature from an average of 49±10 to 73±7 °C, accompanied by considerable fluctuations in the waste mass interstitial oxygen and carbon dioxide concentrations during the first month of storage. Thereafter, steady-state conditions were registered for about 4 months, with an average pile temperature of 77±8 °C, interstitial oxygen concentration varying from below the detection limit up to 5% by volume, interstitial carbon dioxide concentrations varying from 0.2 to 18%, and interstitial methane concentrations varying from below detection limit up to 0.5%. After 6 months of storage, spontaneous combustion occurred in the monitored IND pile. This was preceded by strong winds, which ventilated the pile and increased its oxygen content. Spontaneous combustion was also observed in one RDF pile after the same storage time (about 6 months). The leachate produced as a result of the large quantity of water used in an attempt to douse the burning RDF pile showed higher concentrations of chemical oxygen demand, biochemical oxygen demand, total nitrogen, total oxidized nitrogen, total phosphorus and the heavy metals lead, cadmium and chromium than the median values in the leachate from municipal solid waste (MSW) landfill and from MSW incineration residues (50% fly ash) landfill. Baling to reduce waste fuel porosity is suggested as a safer option for the storage of waste material for energy recovery purposes.

Absorption coefficient of oxide precipitates in silicon wafers after different three-step annealing

Systematic measurements aimed at quantifying the contribution of precipitates to the infrared absorption of silicon are presented here, carried out on wafers with the same initial interstitial oxygen (O i) concentration subjected to three-step treatments. To precisely determine the intensity of the precipitate-related bands, the measurements were performed at liquid He temperature. The results demonstrate the possibility of accounting for the contribution of precipitates in the standard quantitative determination of O i in silicon at room temperature.

Effect of oxygen precipitation on voids in bulk silicon

The effect of oxygen precipitation on flow pattern defects (FPDs) relative to voids in bulk silicon was investigated. FPDs and voids were measured after different annealing time, and with various interstitial oxygen contents and bulk stacking faults (BSFs). It was found that, during annealing, interstitial oxygen in bulk silicon precipitated, however the FPDs density remained constant. The density of BSFs increased with annealing time at 1100 °C. After annealing, the morphology of voids was found to be octahedral with the oxide films inside them, the same as as-grown samples. Therefore, it is concluded that the interstitial silicon atoms released during oxygen precipitation did not enter the voids because of the resistance of the oxide films inside the voids, but condensed into stacking faults. The dissolution of the oxide films is believed to be the principal cause for the annihilation of voids.

A study of the oxygen precipitation kinetics in zirconium-doped silicon

The kinetics of oxygen precipitation at 900 and 1050°C was studied in Czochralski-grown silicon single crystals doped to various levels with zirconium. It is established that zirconium, while not participating in the nucleation of oxygen precipitates, decreases the concentration of interstitial oxygen in the crystals.

Oxygen-related minority-carrier trapping centers in p-type Czochralski silicon

We investigate minority-carrier trapping centers in p-type Czochralski (Cz) silicon by means of the quasi-steady-state photoconductance method. Boron and gallium-doped Cz silicon wafers of varying resistivities and oxygen contamination levels are examined. A clear correlation of the trap density with the interstitial oxygen concentration as well as with the boron and the gallium concentration is detected. The experimental data suggest that oxygen is a direct component of the defect complex responsible for the trapping, while the role of boron and gallium is not fully resolved. Using a simple single-level trapping model, we determine the energy level and the trapping/detrapping time constant ratio of the oxygen-related trapping center.

Effect of Oxygen Content on Grain Growth Kinetics of Titanium

The grain growth kinetics of commercially pure Titanium with different contents of oxygen have been studied. The grain size parameters have been measured by means of the Image Analysis Technique for different heat treatment temperatures and times. The growth exponents and activation energies have been calculated. Finally, tensile tests on the same materials have been carried out. When the interstitial oxygen content in titanium increases the grain growth kinetics and the ductility decrease and the α→β transition temperature, activation energy for grain growth and mechanical strength increase.

Influence of oxygen precipitation on the measure of interstitial oxygen concentration in silicon from the 1207 cm−1 infrared absorption band

The possible use of the absorption band at 1207 cm−1 for the measurement of the concentration of interstitial oxygen (Oi) in silicon samples subjected to a precipitation thermal treatment is discussed. The results of low temperature infrared absorption measurements show that the conversion factor for such evaluation of the residual Oi after precipitation is strongly influenced by the presence of oxide precipitates; a limit value for the concentration of precipitated oxygen is identified, above which the measure becomes unreliable.

Measurement of interstitial oxygen concentration in silicon below 1015 atoms/cm3

The absorption coefficient of silicon at 1118 cm−1 due to the multiphonon contribution related to the combination of two transverse optical and one transverse acoustical phonons is measured at the liquid He temperature. The precise knowledge of this contribution, usually hidden by the absorption band of the unavoidable oxygen impurities, permits the quantitative measurement of interstitial oxygen concentration down to 3×1014 atoms/cm3.

Chemical and structural characterization of oxygen precipitates in silicon by infrared spectroscopy and TEM

Infrared absorption spectra of polyhedral and platelet oxygen precipitates are analyzed using a modified Day–Thorpe approach (J. Phys.: Condens. Matter 11 (1999) 2551). The aspect ratio has been determined by TEM measurements. The reduced spectral function and the stoichiometry are extracted from the absorption spectra and the concentration of precipitated interstitial oxygen. One set of spectra reveal a Fröhlich frequency around 1100 cm −1 and another around 1110–1120 cm −1. It is shown that the shift in the Fröhlich frequency is not due to a different stoichiometry, but due to the detailed structure in the reduced spectral function. The oxygen precipitates consist of SiO γ with γ≈1.1–1.2±0.1.

Process-induced defects in nitrogen doped Czochralski silicon in diode processes

The process-induced defects in nitrogen doped CZ silicon (NCZ-Si) are investigated during diode processes. It was found that in the phosphorous predeposition (1230°C for 2 h), stacking faults and dislocations were formed in NCZ-Si, but in the common CZ silicon (ACZ-Si) only dislocations were observed. In boron diffusion process (1260°C for 30 h), the interstitial oxygen (O i) concentration in NCZ-Si specimens fell to the corresponding solubility and all supersaturated O i was precipitated. On the contrary, only slight oxygen precipitates were generated in ACZ-Si wafers. Correlated to oxygen precipitates, more dislocations were produced in the high resistance active region in NCZ-Si specimens in comparison with ACZ-Si. It is concluded that nitrogen enhances oxygen precipitation during diode processes. In phosphorous predeposition process, these oxygen precipitates in NCZ-Si resulted in not only dislocations, but also stacking faults.

Investigation of Czochralski Silicon Grown with Different Interstitial Oxygen Concentrations and Point Defect Populations

Czochralski silicon crystals, grown with different interstitial oxygen concentrations (group I) or different types of intrinsic defects (group II), were analyzed by X-ray section topography, diffuse X-ray scattering, surface photovoltage, microwave photoconductive decay, and Fourier infrared spectroscopy. The samples of group I showed that the main factor influencing the X-ray section topography images is the amount of precipitated oxygen. The increase in this amount involves a decrease in size and an increase in density of the oxygen precipitates. A strong reduction in the minority carrier diffusion length is observed after precipitation. These effects seem to be dependent on the positions along the ingot axis at which the samples were taken, which would indicate the influence of the sample thermal history on the detectability of oxygen precipitates by means of these techniques. The samples of group II are characterized by vacancy-rich, interstitial-rich, and defect-free regions. After copper decoration, the different defects were observed to have different sizes, densities, shapes, and depth distributions. This feature allows one to clearly distinguish between crystal zones where vacancy or interstitial clusters prevail and where defects are absent. Minority carrier lifetime values are directly related to the defect volume densities. The combined use of different characterization techniques proved itself a powerful tool to study different defect types in Czochralski silicon. © 2001 The Electrochemical Society. All rights reserved.

Intermittent Aeration for In-vessel Composting Of Crab Processing Waste

A crab processing waste/wood shaving mixture was composted in-vessel with four intermittent aeration strategies. The composting process was monitored to assess the efficacy of the aeration methods. Temperature, moisture content and volatile solids of the compost were monitored along with the interstitial oxygen concentration. There was no significant difference in temperature profiles between constant frequency aeration and temperature feedback controlled aeration methods. An increased frequency of aeration resulted in significantly more drying than the less frequent aeration using the same total air volume. Results indicated that air volume could be reduced after the first five days of composting, and the in-vessel composting retention time could be reduced to 15 to 17 days for odor and vermin/vector problems prevention.

Crystal Surface Defects and Oxygen Gettering in Thermally Oxidized Bonded SOI Wafers

This work investigates the role of interstitial oxygen content in the starting Czochralski bonding wafers, and the effects of buried layered implants and thermal processing on the formation of crystalline defects in the surface of bonded silicon on insulator (SOI) material. We found that unimplanted SOI material originating from Si with high oxygen levels were populated with heavy oxygen precipitation and related crystal defects, and were also characterized by low minority carrier lifetime values. However, a dramatic improvement was observed in the behavior of SOI with low oxygen levels where the development of oxygen precipitation in the SOI layer was inhibited. Incorporation of a buried As ion implanted layer in high oxygen level SOI increased the lifetime of the material and suppressed the formation of oxygen precipitates through an oxygen gettering effect. The gettering efficiency of the buried defect layer was found to be related to the dose of the As ion implantation, the annealing temperature, and type of starting silicon material. A dose of was sufficient for effective gettering. © 2001 The Electrochemical Society. All rights reserved.

Degradation of carrier lifetime in Cz silicon solar cells

The lifetime degradation induced by light illumination or carrier injection which is observed in Czochralski-grown silicon (Cz-Si) leads to a significant decrease of solar cell efficiency. Thus, the reduction of this effect has a high potential for the improvement of Cz-Si solar cells. In the present work both, the analysis of the underlying defect and its technological reduction are discussed. A clear correlation of the Cz-specific metastable defect with the oxygen and boron concentration in Cz-Si has been observed. Especially, recently performed lifetime measurements on oxygen-free boron-doped p-type MCz silicon and gallium-doped oxygen-contaminated Cz-silicon, both of which show no degradation, confirm this hypothesis. While the quantitative correlation between the defect concentration and boron is linear, the increase of the defect concentration induced by the interstitial oxygen concentration is superlinear, i.e. it follows a potential law of power approximately 5. Beyond the defect analysis, two different ways to reduce the metastable defect concentration are discussed. A proper material choice by substituting or reducing one of the major components of the metastable defect can completely avoid the degradation effect. The excellent performance of oxygen-free MCz-Si and gallium-doped Cz-Si is reflected in the achieved record efficiencies of 22.7% and 22.5%, respectively. In standard boron-doped oxygen-contaminated p-type Cz-Si a strong reduction of the metastable defect concentration can be achieved by a high-temperature process step resulting in an improvement of the stable bulk lifetime by a factor of 2–4.