铜沉淀对直拉硅单晶中洁净区形成的影响

研究普通热处理和快速热处理工艺下直拉单晶硅中过渡族金属铜杂质对洁净区生成的影响. 通过腐蚀和光学显微镜研究发现,常规高-低-高三步洁净区生成热处理样品中, 第一步高温热处理前对样品铜沾污,样品中没有洁净区生成,高密度的铜沉淀布满了样品整个截面. 而第二步、第三步热处理过程中引入铜杂质不影响洁净区的生成. 研究表明,高温热处理过程中生成的铜沉淀不能溶解是导致洁净区不能形成的最主要原因. 另外,由于不同温度下热处理,导致引入铜杂质的平衡浓度不同,会在一定程度上影响洁净区的厚度. 对于快速热处理样品,可以得到相似的结果. 关键词： 直拉单晶硅 铜沉淀 洁净区     

Atomic-scale computer simulation study of the interaction of Cu-rich precipitates with irradiation-produced defects in α-Fe

Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can, therefore, be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu–Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model: both vacancy and interstitial defects in metals may bind to precipitates with weaker cohesion than the matrix.     

退火直拉硅单晶中氧沉淀和诱生缺陷的电子显微镜研究

本文用超高压透射电子显微镜研究退火的高氧含量无位错直拉硅单晶中氧沉淀和诱生缺陷。在750—1050℃范围内氧沉淀是球状的α方英石。除了球状氧沉淀粒子之外还有一些具有{001}惯习面的方片状氧沉淀物。在950℃以上沿〈110〉方向从氧沉淀发射出冲压式棱柱位错环。这些位错环的柏氏矢量为α/2〈110〉、环面法线为〈110〉,它们是间隙型的位错环。这些位错环是从方片状氧沉淀物或从球伏氧沉淀粒子的聚集团发射出来的。当它们遇到障碍物时可能产生比较复杂的位错组态。实验中观察到由于层错攀移形成的台阶。热处理温度在850℃以下时,未观察到体内层错。 关键词：     

Quantitative analysis of fine nano-sized precipitates in low-carbon steels by small angle neutron scattering

The small angle neutron scattering (SANS) technique was used to determine the nano-sized precipitates in interstitial free (IF) and low-carbon (LC) steels with a hot-rolling temperature. The real-space direct model fitting method was applied to quantitatively analyze the SANS data. The magnetic and chemical properties of precipitates in the samples were also investigated by separation and comparison of nuclear and magnetic SANS scattering data. The size distribution of precipitates in the IF steel is in good agreement with the microstructure observation using transmission electron microscopy. The results revealed that the IF steel had two types of non-magnetic precipitates, Ti₄C₂S₂ and TiC, with the average size of about 30 nm in diameter and little difference in chemical composition. In case of commercial LC steel, the fine and large precipitates are identified as MnS and Fe₃C, respectively. The average size of spherical MnS precipitates was about 4.8 nm in radius and the distribution is isotropic. It is likely that the LC steels have almost the same composition and a similar size as precipitates such as MnS and Fe₃C with different finishing delivery temperatures. Interestingly, the average size and volume fraction of fine precipitates showed no significantly changes under the different finishing delivery temperatures.     

Impact of nickel contamination on carrier recombination in n- and p-type crystalline silicon wafers

The effect of Ni surface contamination on carrier recombination after high temperature processing of crystalline silicon wafers has been studied for a range of n- and p-type resistivities. The results suggest that the presence of Ni precipitates at the wafer surfaces, formed during cooling, dominate the measured lifetimes. These precipitates exhibit a greater impact on the low-injection lifetime in p-type samples than in n-type. In addition, the injection-dependent lifetime curves for the n-type samples changed from increasing to decreasing with injection-level as the resistivity increased above approximately 10 Ω cm. In most cases, the surface recombination velocity attributable to the presence of these Ni precipitates at the oxidized surfaces increased linearly with the Ni dose. PACS 72.20.Jv; 73.20.Hb; 71.55.Cn     

Effect of disperse particles on the formation of defectless channels and the deformation stability of neutron-irradiated metals

Dislocation-kinetics equations are used to consider the effect of precipitates and disperse particles on the conditions of formation of defectless channels and the appearance of a yield drop and a yield plateau in the stress-strain curves of neutron-irradiated metals and alloys. It is found that, at a volume particle concentration higher than a certain critical value depending on the radiation dose, channels do not form and the yield drop and yield plateau in the stress-strain curves disappear. A high concentration of disperse particles in a metal strongly decreases the uniform strain above which plastic instability in the form of a neck appears in a tensile specimen. The theoretical results are illustrated by available experimental data for copper and copper alloys.     

硅单晶中铜沉淀物的几何形态

本文利用红外显微镜和化学浸蚀的方法,研究了硅单晶中铜沉淀物的几何形态。实验表明,用红外显微镜观察到的各种形态的沉淀物是由{110}面上的片状沉淀组成的,样品的性质对它的形态没有影响。 关键词：     

Correlation between extrinsic defects and physical properties in incommensurate systems

A non-exhaustive survey of the influence of extrinsic defects (such as dislocation lines, substitutional or interstitial impurities and precipitates) on the physical properties of incommensurate systems is presented; special attention is paid to incommensurate insulators having a displacive modulation. Direct-imaging techniques such as X-ray Topography and Transmission Electron Microscopy are shown to be very fruitful tools in order to characterize the texture of the phase front at the lock-in transition, the mechanisms of the modulation wave-vector variation with temperature and the pinning action exerted by extrinsic defects of the crystal.     

Comparison of different gettering techniques for Cu–p+ versus polysilicon and oxygen precipitates

We performed measurements of gettering efficiencies for Cu in silicon wafers with competing gettering sites. Epitaxial wafers (p/p+) boron-doped with a polysilicon back side allowed us to compare p+ gettering with polysilicon gettering. We further measured metal distributions in p+/p- epitaxial test wafers, with the p- substrate wafers pretreated for oxygen precipitation to compare p+ gettering with oxygen precipitate gettering. Our test started with a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by thermal treatment in order to redistribute the metallic impurity. Wafers were then analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. This led to “stratigraphical” concentration profiles of the impurity, with typical detection limits of 5–10×10¹² atoms/cm³. Twenty-five percent of the total Cu contamination in the p/p+/poly wafer was found in the p+ layer, whilst 75% was gettered by the polysilicon. Obviously, polysilicon exhibits a stronger gettering than p+ silicon, but due to the large distance from the front surface, polysilicon was less effective in reducing impurities from the front side of a wafer compared with p+ gettering. An epitaxial layer p+ on top of p- substrates with oxygen precipitates gettered 50% of the total Cu; while the other 50% of the Cu was measured in the p- substrate wafer with oxygen precipitates. Without oxygen precipitates, 100% of the spiked Cu contamination was detected inside the p+ layer. Gettering by oxygen precipitates thus occurs in the same temperature range as that where p+ silicon begins to getter Cu. Received: 3 September 2001 / Accepted: 17 October 2001 / Published online: 27 March 2002     

One-pot production of copper ferrite nanoparticles using a chemical method

Copper ferrite nanoparticles were synthesized via the oxidation of precipitates obtained from the reaction of FeCl₂, CuSO₄ and N₂H₄ in the presence of gelatin. These copper ferrite particles were subsequently examined using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Mössbauer spectroscopy. The average size of the copper ferrite nanoparticles was less than 5 nm, and they exhibited superparamagnetic behavior as a result of their small size. The low temperature Mössbauer spectrum exhibited three sets of sextets, two corresponding to the tetrahedral and octahedral sites of the copper spinel structure and one with small hyperfine magnetic field corresponding to the surface or defects of the nanoparticles. When the ratio of copper salt was increased, the tetrahedral site became preferable for copper, and metallic copper and copper ferrite were both present in a single nanoparticle.     

Structure,impurity composition,and photoluminescence of mechanically polished layers of single-crystal silicon

The introduction of optically active defects (such as atomic clusters, dislocations, precipitates) into a silicon single crystal using irradiation, plastic deformation, or heat treatment has been considered a possible approach to the design of silicon-based light-emitting structures in the near infrared region. Defects were introduced into silicon plates by traditional mechanical polishing. The changes in the defect structure and the impurity composition of damaged silicon layers during thermal annealing (TA) of a crystal were examined using transmission electronic microscopy and x-ray fluorescence. Optical properties of the defects were studied at 77 K using photoluminescence (PL) in the near infrared region. It has been shown that the defects generated by mechanical polishing transform into dislocations and dislocation loops and that SiO₂ precipitates also form as a result of annealing at temperatures of 850 to 1000°C. Depending on the annealing temperature, either oxide precipitates or dislocations decorated by copper atoms, which are gettered from the crystal bulk, make the predominant contribution to PL spectra.     

Rapid-thermal-anneal-based internal gettering for?germanium-doped Czochralski silicon

The internal gettering (IG) effects involved with a rapid thermal anneal (RTA) in germanium-doped Czochralski silicon (GCz-Si) wafer have been investigated. It was found that germanium doping could enhance the oxygen precipitation in bulk while shrinking the denuded zone width near the surface through pre-RTA at high temperature plus low–high temperature conventional furnace anneals. Rapid cooling rate after RTA was clarified to be beneficial for oxygen precipitation for GCz-Si wafer. It was suggested that the germanium doping could increase the vacancy concentration in Cz-Si during RTA by forming the germanium–vacancy complexes. In contrast to that in Cz-Si wafer, the smaller-sized higher-density oxygen precipitates were presented in the nucleation anneals, then followed RTA pretreatment while more oxygen precipitates survived during ramping processes after nucleation anneals in the GCz-Si wafer. Enhanced heterogeneous nucleation and reduced critical radius of precipitates associated with the germanium–vacancy complexes have been proposed for the oxygen precipitation enhancement.     

Effect of copper on dislocation luminescence centers in silicon

The effect of copper on dislocation luminescence centers in silicon has been investigated using photoluminescence and transmission electron microscopy. It has been demonstrated that there exist two main mechanisms responsible for quenching of dislocation luminescence by the copper impurity. The first mechanism is dominant at high copper concentrations and associated with the decrease in the time of nonradiative recombination of nonequilibrium charge carriers due to the formation of copper precipitates in silicon. This leads to the quenching of the entire dislocation luminescence and the edge exciton luminescence. The second mechanism is associated with the interaction of individual copper atoms with deep dislocation centers D1/D2, which results in the passivation of the recombination activity of these centers. This mechanism takes place even at room temperature and is highly effective at low copper concentrations.     

Accelerated oxygen precipitation in fast neutron irradiated Czochralski silicon

Annealing effect of the oxygen precipitation and the induced defects have been investigated on the fast neutron irradiated Czochralski silicon （CZ-Si） by infrared absorption spectrum and the optical microscopy. It is found that the fast neutron irradiation greatly accelerates the oxygen precipitation that leads to a sharp decrease of the interstitial oxygen with the annealing time. At room temperature （RT）, the 1107cm^-1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. At low temperature, the infrared absorption peaks appear at 1078cm^-1, 1096cm^-1, and 1182cm^-1, related to different shapes of the oxygen precipitates. The bulk microdefects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self-interstitial atoms are created and aggregate with oxygen precipitation.     

The effect of oxygen on the electrical properties of silicon

Interstitial oxygen present in solution, as detected by the 9 μ absorption band, increases the Hall mobility of electrons in n-type silicon crystals but decreases the Hall mobility of holes in p-type. These results are explained by the lattice strain produced via dissolved interstitial oxygen impurities. Results on samples saturated with oxygen and heat treated to cause precipitation of SiO₂ in the temperature range of 950–1250°C show that the SiO₂ particles decrease the values of Hall mobility compared to the initial values on samples without precipitates. Re-annealing causes the dissolution of the precipitates and recovery nearly to the initial values of the Hall coefficient.     

The lattice structure of antiferromagnetic γ-iron

Coherent precipitates of γ-iron in a copper matrix have been investigated by X-ray diffraction in the temperature range from 300 to 6 K. Below the temperature of the antiferromagnetic ordering (T_N ≈ 70 K) a shift and a splitting of the Bragg-peaks are observed indicating a reduction of the symmetry of the fcc lattice of the γ-iron and a small increase of the atomic volume by 0.3%. The details of the complex diffraction pattern at low temperatures can be explained by a tetragonal distortion of the lattice (≈0.5% difference of the cube axes) in combination with a periodic domain structure with domain sizes of about 9 nm.     

Interaction of dislocations with nanoprecipitates of the metastable phase and dispersion strengthening of the Fe-Cu alloy

The interaction of dislocations with copper-enriched precipitates in the matrix of body-centered cubic iron has been investigated by the molecular dynamics method. It has been shown that dislocations stimulate the development of a phase instability of body-centered cubic copper precipitates in a specific range of their sizes. This process is accompanied by the pinning of dislocations by precipitates and makes a significant contribution to strengthening. The results obtained provide an adequate explanation for the observed dependence of the strengthening in the Fe-Cu system on the precipitate size.     

Magnetic and mechanical properties of Cu-strengthened aged HSLA-100 steel

Magnetic and mechanical properties were evaluated for various heat-treated Cu-strengthened HSLA-100 steels. After austenitizing at 1183?K for one hour and then water quenching, the material was aged at different temperatures ranging between 623?K and 973?K for one hour. Scanning and transmission electron microscopes with an energy dispersive X-ray attachment were used for microstructural analysis. Nanosize coherent copper precipitates caused an increase in hardness with increase in ageing temperature. The steel exhibited maximum hardness at 773?K followed by decrease in hardness with over-ageing. Copper precipitates coarsened and lost coherency during over-ageing. Ageing behaviour again exhibited an increase in hardness at 973?K due to the formation of new martensite islands. Magnetic hysteresis loop and magnetic Barkhausen emissions techniques were used to characterize the aged materials. No correlation was observed between the magnetic parameters and hardness. The results were explained by the fact that nanosize Cu precipitates, the size of which is much smaller than the domain wall width, did not influence the magnetic domain dynamics.     

Agglomeration of As antisites in As-rich low-temperature GaAs: nucleation without a critical nucleus size

To investigate the early stages of nucleation and growth of As precipitates in GaAs grown at low substrate temperature, we make use of a self-consistent-charge density-functional based tight-binding method. Since a pair of As antisites already shows a significant binding energy which increases when more As antisites are attached, there is no critical nucleus size. Provided that all excess As has precipitated, the clusters may grow in size since the binding energies increase with increasing agglomeration size. These findings close the gap between experimental investigation of point defects and the detection of nanometer-size precipitates in transmission electron microscopy.     

Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.