Loss Of Interstitial Oxygen Research Articles

Ring‐Like Defect Formation in N‐Type Czochralski‐Grown Silicon Wafers during Thermal Donor Formation

This article presents experimental and simulation studies on the formation of recombination‐active ring‐like defects during thermal donor (TD) formation at 450 °C in n‐type Czochralski‐grown silicon wafers. With increasing anneal duration from 1 to 24 h, the resistivity and interstitial oxygen concentration of samples decrease, consistent with the formation of TDs. However, after a subsequent TD annihilation treatment, the resistivity recovers completely, while the interstitial oxygen concentration recovers only partially. Furthermore, the wafers exhibit ring‐like defects in photoluminescence images after the TD generation and remain persistent even after annihilation treatment. By applying a tabula rasa (TR) treatment prior to TD generation anneals, the net loss of interstitial oxygen is reduced, and the incubation time of the ring‐like defects is extended in comparison to as‐grown wafers. Finally, to investigate the possibility of low‐temperature precipitation, simulation of oxygen precipitation (OP) kinetics during the 450 °C annealing steps is performed using an enhanced effective diffusivity of oxygen. These simulations demonstrate that OP can occur simultaneously during TD formation, resulting in recombination‐active ring‐like defects.

Electrochemical properties of doped lantanum–nickelate-based electrodes

This work is devoted to the studying of effects of La2NiO4 doping with alkaline-earth elements: Ca, Sr, and Ba (at an amount of 15 mol %) on its structural, electrical, and electrochemical properties. The effects of the alkaline-earth element nature, introduction of the Ce0.8Sm0.2O1.9-electrolyte (SDC) component to the functional layer, and the presence of collecting film onto electrochemical activity of the electrodes contacting the Ce0.8Sm0.2O1.9-electrolyte are examined. The doping was found to increase the La2NiO4 full conductivity due to increase in the hole conductivity. The maximal conductivity (at the sample density of 86–89%) was obtained for the Ca-doped composition: 85 S/сm at 700°C, as compared with 65 S/сm for undoped La2NiO4. at the same time, the doping was found to deteriorate the electrodes’ electrochemical activity which is likely to be due to loss of interstitial oxygen as a result of the doping. The using of composite electrodes allows increasing polarization conductivity markedly. For instance, at 700°С the conductivity of La2NiO4 is 0.25 S/сm2; of its based composite, 0.67 S/сm2.

Microstructure and compressive properties of directionally solidified Er-bearing TiAl alloy using cold crucible

Dual phase γ-TiAl of Ti-47Al-2Nb-2Cr was alloyed by erbium and then prepared by directional solidification using electromagnetic cold crucible. Compression test was performed to determine the work hardening capacity in accordance with microstructures regarding erbium additions. The directionally solidified columnar grains were refined by 0.2at.% erbium in comparison to those without erbium, while columnar to equiaxed transition (CET) happened in the case of 0.8at.% erbium. Since oxygen has extremely strong affinity to erbium, oxygen dissolved in the TiAl matrix decreased from 940ppm to 560ppm by internally oxidizing of erbium. The scanning electron microscopy characterization revealed that the Er2O3 particles were dispersed uniformly in the (α2+γ) lamellae. Arising from the loss of interstitial oxygen in the matrix, stacking fault energy of the h.c.p. phase (α2 or α) was decreased which resulted in increasing nucleation sites of γ phase. Then the γ lamellae were refined in the Er-bearing alloys. During the compression test, the work hardening capacity (Hc) of the 0.2at.% Er-bearing alloy was improved at strain rate ε̇ of 10−1–10−3s−1, which could be fitted as Hc=1.66ε̇−0.05. Besides, the governing deformation mechanism of the Er-bearing TiAl alloy was the same as the Er-free TiAl alloy according to the strain rate sensitivity results.

The effect of oxide precipitates on minority carrier lifetime in n-type silicon

Supersaturated levels of interstitial oxygen in Czochralski silicon can lead to the formation of oxide precipitates. Although beneficial from an internal gettering perspective, oxygen-related extended defects give rise to recombination which reduces minority carrier lifetime. The highest efficiency silicon solar cells are made from n-type substrates in which oxide precipitates can have a detrimental impact on cell efficiency. In order to quantify and to understand the mechanism of recombination in such materials, we correlate injection level-dependent minority carrier lifetime data measured with silicon nitride surface passivation with interstitial oxygen loss and precipitate concentration measurements in samples processed under substantially different conditions. We account for surface recombination, doping level, and precipitate morphology to present a generalised parameterisation of lifetime. The lifetime data are analysed in terms of recombination activity which is dependent on precipitate density or on the surface area of different morphologies of precipitates. Correlation of the lifetime data with interstitial oxygen loss data shows that the recombination activity is likely to be dependent on the precipitate surface area. We generalise our findings to estimate the impact of oxide precipitates with a given surface area on lifetime in both n-type and p-type silicon.

Surface Oxygen Exchange Properties of Sr Doped La2NiO4+δ as SOFC Cathode: Thin-Film Electrical Conductivity Relaxation Investigation

Roddlesden-Popper Phases, such as La2NiO4, have been proposed as promising intermediate temperature SOFC cathodes, due to their high surface oxygen exchange and bulk diffusivities. However, relatively low electrical conductivity of LNO phase is a concern for its application. It has been shown that Sr doping is an effective way to improve LNO’s electrical conductivity, but it is important to investigate the effect of such doping on other properties such as oxygen surface exchange coefficient. In this study, Sr doped lanthanum nickelates i.e., La2-xSrxNiO4+δ (0≤x≤0.4) thin and dense films on dense thick GDC (~1mm) substrate, were prepared by using spray-modified pressing method. The surface oxygen transport kinetics was investigated by electrical conductivity relaxation (ECR) technique. Since the thickness of thin films is ~15μm, much less than the characteristic length of LNO, the oxygen transport kinetics are controlled by the surface exchange steps and the oxygen ion concentration is uniform in the film at any time during the ECR process. Such situation enables a more accurate fitting results compared to the traditional fitting procedure based on thick pellets, because only k value is the unknown parameter. The fitted k for LNO is 4.02×10-5cm/s at 0.2atm 700oC, which decreases with lowered oxygen partial pressure. Sr doping harmed the surface exchange kinetics, k of Sr40 is about one order of magnitude smaller than undoped one. Interstitial oxygen and Ni oxidation state are suggested to be predominant roles in determining the surface kinetics. Both Sr doping and lowered oxygen partial pressure lead to the loss of interstitial oxygen and the oxidation of Ni2+, resulting the lowered surface exchange rate.

Characterizing and modeling the evolution of silicon oxide precipitates during thermal cycles

The effects of oxidizing annealing cycles on Si high-quality wafers (as used to monitor IC production tools or SOI applications) were studied using different techniques (nano-scale observations and chemical analysis in Transmission Electron Microscope (TEM), but also large scale measurements, such as Laser Scattering Tomography (LST) and chemical etching (CE), thus coupling local analyses with global measurements of defects density and size) to determine their characteristics. Interstitial oxygen loss during cycles was also measured using Fourier Transform Infra-Red spectroscopy (FTIR).It appeared that each cycle is composed of a defect nucleation stage and a growth stage, and that the distribution of these defects (mainly oxide precipitates) along wafer radius essentially depends on the initial point defect density. The evolution of these precipitates was described by a diffusion-and-growth model derived from Ham's model and taking into account various phenomena: oxygen loss, point-defect distribution and cycle effects (up/down ramp and high-temperature plateau). Extensions and limits of the model are also discussed.

Studies of influence of high temperature preannealing on oxygen precipitation in CZ Si wafers

We have investigated Czochralski grown low boron doped silicon wafers after oxygen precipitation using high temperature preannealing. Wafers originating from the part of the silicon ingot close to head and close to tail were used for the experiments representing different temperature history of the wafers. The loss of interstitial oxygen, precipitate morphology and stoichiometry at various stages of precipitation were determined by infrared absorption spectroscopy at liquid nitrogen and at room temperature. The impact of a high temperature preannealing at various temperatures on the parameters of precipitates including also their concentration determined from chemical etching was observed during the growth of oxygen precipitates. The obtained results were compared with transmission electron microscopy.

Precipitation in silicon wafers after high temperature preanneal studied by X-ray diffraction methods

We have investigated oxygen precipitation in Czochralski silicon wafers focusing on influence of nucleation temperature and high temperature pre-anneal during common three step treatment. Thick Si wafers were studied mainly by x-ray diffraction in Laue transmission geometry using Mo x-ray tube, but were also compared to reciprocal space maps obtained in Bragg reflection geometry. The analysis of measured diffraction scans in Laue geometry was performed by means of Takagi equations and statistical dynamical theory of diffraction. From the simulated Laue diffraction curves we find the size of the individual defect area and the fraction of strain area volume in the wafer. The results obtained from x-ray diffraction were compared to loss of interstitial oxygen according to infrared absorption spectroscopy and the size of SiO2 precipitate core was estimated. These techniques are in agreement with transmission electron microscopy images.

An attempt to specify thermal history in CZ silicon wafers and possibilities for its modification

The term thermal history of silicon wafers represents the whole variety of process parameters of crystal growth. The aim of this contribution is an attempt to specify thermal history by one parameter that is directly correlated to the bulk microdefect density. The parameter that reflects thermal history and correlates it with nucleation of oxide precipitates is the concentration of VO 2 complexes. The VO 2 concentration in silicon wafers is too low to be measured by FTIR but it can be obtained from the loss of interstitial oxygen during a standardized thermal treatment. Based on this, the vacancy concentration frozen during crystal cooling in the ingot can be calculated. RTA treatments above 1150 °C create a well defined level of the VO 2 concentration in silicon wafers. This means that a well controlled modification of the thermal history is possible. We also investigated the kinetics of reduction of the as-grown excess VO 2 concentration during RTA treatments at 950 °C and 1050 °C and the effectiveness of this attempt to totally delete the thermal history.

Oxygen loss and thermal double donor formation in germanium

Kinetics of interstitial oxygen loss and oxygen-related thermal double donor (TDD) generation upon heat treatments of Ge:O crystals at 350 °C have been studied. The TDD concentration ( N TDD) was derived from Hall effect measurements in the temperature range 77–400 K. The bistability of the first TDD species was taken into account. The interstitial oxygen concentration ([O i ]) in the crystals was determined from measurements of the intensity of the infrared absorption band at 855 cm −1 at room temperature with the use of a recently obtained calibration coefficient C O=1.05×10 17 cm −2. From an analysis of the [O i ]( t) and N TDD( t) kinetics a confirmation of recent suggestions about faster diffusivity of small oxygen clusters compared to the diffusivity of single interstitial oxygen atoms was obtained. Average numbers ( N) of oxygen atoms lost per TDD species created, N=Δ[O i ]/ N TDD, were calculated at different stages of the TDD generation. The obtained values of N are consistent with those expected in accordance with the recent models of the TDD structure. In particular, an average number of oxygen atoms per TDD species was about 5 at initial stages of the heat treatment when the first members (the TDD2 and TDD3 species) of the TDD family were dominant. N was found to be about 10 after extended anneals at 350 °C when the TDD6 and TDD7 species were dominant.

Combination of optical measurement and precipitation theory to overcome the obstacles of detection limits

Ham's theory was applied in order to become independent of detection limits for oxide precipitates and to quantify the phenomenon of oxygen loss to invisible BMDs during thermal treatments. The density of detectable bulk micro-defects (BMDs) depends on the size distribution of grown-in nuclei and the ramp rate, temperature, and duration of the thermal treatment applied. There is no correlation to the invisible BMDs. During conventional annealing, the density of the invisible BMDs decreases exponentially with increasing radius of precipitates at a nearly constant loss of interstitial oxygen. Only if the calculated radius exceeds 70 nm, a 100% loss of interstitial oxygen to BMDs detectable by scanning infrared microscopy (SIRM) seems to be possible. After RTA processing at 1230 °C, a period of 1 h at 1000 °C would be necessary for the growing oxide precipitates to reach a saturated density detectable by SIRM, but there remains a very high density of invisible BMDs consuming interstitial oxygen. In N-doped silicon, the vast majority of BMDs is detectable by SIRM, cleave and etch, and infrared light scattering tomography after thermal processing.

Infrared analysis of the precipitated oxide phase in silicon and germanium

Oxygen-doped germanium samples have been subjected to a prolonged precipitation treatment in the 560–620 °C temperature range. Broad infrared absorption bands with maxima at 865 and 884 cm −1 which develop proportionally with the loss of interstitial oxygen are observed and are attributed to germanium oxide precipitates. Secondary peaks appear at 675 and 958 cm −1. The broad absorption bands are analyzed using a procedure which was previously applied to SiO x precipitates in silicon. Similarly as in silicon, the absorption in germanium may be fitted assuming the presence of polyhedral and platelet GeO x precipitates, with relative occurrence depending on the details of the thermal treatment.

Depth profile of thermal donors in NTDCZSi

The depth profile of thermal donors (TDs) produced by annealing neutron transmutation-doped Czochralski silicon (NTDCZSi) at high temperatures above 1000 °C first and then at 450 °C has been studied by means of the thermal conversion spreading resistance (TCSR). The concentration of the TDs increases with the distance from the surface of the sample, and its depth profile can be described by the error function when the annealing temperature is low or the annealing time is short. A peak is formed in the depth profile under the annealing condition of 1100 °C for 4 h. Combining with an infrared absorption study, it is found that the curves of the diffusivity coincide with the loss of interstitial oxygen. These results indicate that the distribution of the TDs depends on both the out-diffusion and the precipitation of oxygen. Neutron irradiation accelerates the out-diffusion of the oxygen in the surface region of the silicon and the oxygen precipitation in the bulk.

The impact of platelet oxygen precipitates in silicon on the junction leakagecurrent and the interstitial oxygen loss

The impact of oxide precipitates (OPs) on the p–n junction leakage currentdensity for reverse voltage is studied for the case of oxygen precipitation in siliconin the form of oxide platelets, typical for 650–1000°C treatment. A method isproposed which takes into account the precipitate morphology and the oxidestoichiometry for the extraction of leakage densities related to various parts of thedefect structure, namely to: (i) the platelet planes, (ii) the sidewalls ofplatelets, and (iii) the dislocations formed as secondary defects. It is alsoshown that the impact of platelet OPs on junction leakage is expected tobe dependent on the isolation scheme used for junction manufacturing.

Interstitial oxygen loss and the formation of thermal double donors in Si

The combination of first-principles total energy calculations and a general kinetic model, which takes into account all processes of association, dissociation, and restructuring, is used to study the kinetics of thermal double donors (TDDs) in silicon over the temperature range of 300–650 °C. A strong correlation is found between the formation rate of TDDs and the loss rate of interstitial oxygen atoms. Also, a close agreement with experiments is obtained. It is found that TDDs grow via consecutive reactions where fast diffusing oxygen dimers and all TDDs capture interstitial oxygen atoms.

Infrared vibrational mode absorption from thermal donors in germanium

The infrared vibrational absorption attributed to thermal donors (TDs) in Ge has been investigated. Oxygen-doped Ge was annealed at 350°C and the spectrum was recorded after different annealing times. Absorption bands develop mainly around 600 and 780cm−1, in close correspondence with the increasing TD concentration and the loss of interstitial oxygen (Oi). At low temperature the bands are resolved into a number of components which appear sequentially and are assigned to the double donor configuration of TD2–TD9. The assignments are confirmed by the bistable properties of TD2–TD4 revealed in the vibrational spectrum. The low-energy configuration gives rise to three new bands in the same range. The absorption is interpreted as due to vibrational modes of oxygen incorporated in the TDs. The number of oxygen atoms involved is discussed taking account of the evolution of the Oi and TD concentrations and of the integrated absorption.

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.

The Effect of Pressure on the Concentration of Thermal Donors in Czochralski Grown Silicon

AbstractWe have investigated the effect of annealing at temperatures up to 1230 K under hydrostatic argon pressure up to 1.1 GPa on thermal donor formation and on interstitial oxygen precipitation in Czechralski grown silicon. Depending on annealing temperature and applied pressure, the stressen‐hanced formation of thermal donors, enhanced interstitial oxygen loss from the Si‐O solid solution, and generation of oxygen‐related defects were observed.

Investigation of oxygen precipitation related crystal defects in processed silicon wafers by infrared light scattering tomography

Infrared light scattering tomography (IR-LST) was used to study microdefects in processed silicon wafers. Both p- and n-type CZSi substrates with different initial oxygen concentrations from 7× 1017 to 11 × 1017 cm−3 were used. A variety of thermal pretreatments and their influence on the defect generation in a diode process were studied. Extended secondary defect formations like stacking faults with their surrounding Frank-loop and prismatic punching systems were identified directly by IR-LST. Correlations between defect densities obtained for different sizes of defects and the initial concentration of interstitial oxygen and the loss of interstitial oxygen during processing, respectively, have shown that the concentration and size of as-grown nuclei is strongly affecting the defect generation after different thermal pretreatments. The inverse effective carrier lifetime depends linearly on the defect density obtained by IR-LST.

The role of rapidly diffusing dimers in oxygen loss and the association of thermal donors with small oxygen clusters

The loss of interstitial oxygen from solution is shown to exhibit second order kinetics provided dimer dissociation is not significant at the anneal temperature. Measured changes in the kinetics of the process for anneals at T ⩾ 450 °C can be explained by the increasing effect of this dissociation provided dimers diffuse much more rapidly than isolated atoms and are trapped efficiently. The magnitude of the changes indicates that weakly bound clusters are responsible for this trapping. The formation of two separate series of oxygen clusters containing odd and even numbers of oxygen atoms would be a consequence of clustering by dimer addition. The assignment of thermal donors to the odd-numbered series is suggested.