Dislocations In Silicon Crystals Research Articles

FEATURES OF MECHANICALLY STIMULATED CHANGES IN THE ELECTRICAL CONDUCTIVITY OF P-Si CRYSTALS AFTER THE ACTION OF A MAGNETIC FIELD

The research investigated mechanically stimulated changes in resistance ( R/R 0 = f(σ) ) of p -type conductivity single-crystal silicon samples that underwent long-term (~ 600 days) magnetic treatment. The permanent magnetic field induction was В = 0.354 Т . It was established that the action of the magnetic field leads to the appearance of a characteristic maximum on the curves R/R 0 = f(σ) at the initial stage of uniaxial elastic deformation. A similar effect was observed after small doses of X-irradiation ( D = 312 Gy ). It was found that the position and magnitude of the characteristic maximum on the R/R 0 = f(σ) curves significantly depend on the time that has passed since the previous cycle of deformation (compression-decompression). In particular, it is shown that the characteristic maximum is not observed if this time does not exceed 20 hours. It was also found that with an increase in time (which has passed since the previous deformation cycle), the value of the maximum increases, and its position shifts towards higher mechanical stresses σ . At the same time, the amount of residual resistance at the beginning of the next deformation cycle also decreases. So, it can be seen that the relaxation processes, which are accompanied by a change in the value of the residual resistance of the crystal, do not have a clear time periodicity, but there is a clear tendency to its increase in value. The change of the defective background in the crystal under the action of the load and the magnetic field affects the concentration and mobility of the charge carriers, which are related to the electrical conductivity of the semiconductor. A characteristic feature of dislocations in silicon crystals is the presence around them of areas with an increased concentration of point defects (Cottrell clouds). It has been confirmed that the long-term effect of a constant magnetic field on experimental p -Si crystals leads to the disintegration of defects, such as hydrogen-containing and oxygen-containing complexes (Si–O–Si, Si–H 2 , O–Si–O, Si–O–C, Si –CH 3 , H–OH, H 2 O, Si–OH, etc.). As a result of such decay, the formed hydrogen can migrate in the elastic stress fields of the near-surface layer, passivating the acceptor bonds. This, accordingly, leads to a decrease in the surface electrical conductivity of the experimental samples. Key words : silicon, magnetic field, dislocations, uniaxial elastic deformation.

INVESTIGATING THE IMPACT OF AN EXTERNAL INFLUENCE ON THE DYNAMIC BEHAVIOR OF DISLOCATIONS IN SILICON CRYSTALS

The results of studying of the influence of a constant magnetic field on the dynamic behavior of dislocations in the crystalline block of an interferometer subsequently subjected to uniaxial mechanical tensile stress along the crystallographic axis of silicon are presented. The periodicity of the dilatation moire image after these influences, the average means free path of a dislocation in a crystal (block), the amount of slip, the average density of dislocations along the slip line, the relative deformation, and Young's modulus are calculated. To study the effect of a stable magnetic field on the dynamic behavior of dislocations in silicon crystals, a special three-block X-ray interferometer was fabricated in one of the blocks, and dislocations were introduced using the technique proposed by us. The experiments were carried out for various values of the magnetic field induction and mechanical stress. It is shown that the sequential action of these external influences leads to an increase in the starting stress, a decrease in the velocity of dislocation movement, a delay in the onset of dislocation movement, and the appearance of a hardening phenomenon. Experiments show that the displacement mobility characteristics are especially sensitive when the modulus of the magnetic induction vector reaches a certain threshold value for a given sample. It was shown that, in a sample containing silicon dislocations, the magnetic memory that appears after storage in a magnetic field is short-lived. It is found that the speed of movement of a dislocation in a magnetic field processed by a magnetic field, "then" subjected to mechanical stress (stretching), changes, but in practice the energy of its activation does not change. A theoretical analysis of the above experimental results is carried out, their scientific substantiation is given, all the factors associated with the phenomena observed in experiments are revealed.

X-ray Interferometric Study of the Effect of a Constant Magnetic Field on the Dynamic Behavior of Dislocations in Silicon Crystals

The results of studying the influence of a constant magnetic field on the dynamic behavior of dislocations in the crystal block of an interferometer, which is in a magnetic field and subsequently subjected to uniaxial mechanical tensile stress along the crystal axis [1 $$\bar {1}$$ 0], are presented. It is experimentally proved that in silicon crystals that have undergone preliminary magnetic treatment, a hardening effect is observed. The magnetic memory that appears in silicon samples with dislocations after exposure to a magnetic field is shown to be short term.

Role of migration barriers in the dynamic behavior of short surface dislocations in silicon crystals

The influence of migration barriers on the mobility of short surface dislocations (length L of ≤100 μm) in Si crystals is analyzed in this paper. The dependence of the migration barrier on the diffusion coefficient of impurities that are dominant in Si after surface metallization is established.

X-ray and magnetic-field-enhanced change in physical characteristics of silicon crystals

The effect of low-energy (W = 8 keV) low-dose ((0.3–7.3) × 102 Gy) radiation and a dc magnetic field (B = 0.17 T) on structural, micromechanical, and microplastic characteristics of silicon crystals has been studied. The features in the dynamic behavior of dislocations in silicon crystals, which manifest themselves upon only X-ray exposure and combined (X-ray and magnetic) exposure, have been revealed.

Interaction of dopant atoms with stacking faults in silicon

The width of a stacking fault ribbon bound by a pair of partial dislocations in silicon crystals was unchanged when boron and gallium atoms of p-type dopant were agglomerated nearby the ribbon by annealing, even though the width increased when n-type dopant atoms were agglomerated as previously reported [Y. Ohno, Y. Tokumoto, I. Yonenaga, Thin Solid Films, accepted for publication]. The origin of the width-increase in n-type crystals was proposed as the reduction of the stacking fault energy, from 58±5 down to 46±5mJ/m2, due to an electronic interaction between the ribbon and the n-type dopant atoms, and the interaction energy was estimated to be 0.15±0.05eV. On the other hand, the interaction of p-type dopant atoms with stacking faults was not detected.

3-D structures of crack-tip dislocations and their shielding effect revealed by electron tomography

Three-dimensional structures of crack-tip dislocations in silicon crystals have been examined by combining scanning transmission electron microscopy and computed tomography. Cracks were introduced by a Vickers hardness tester at room temperature, and the sample was heated at 823 K for 1 h in order to introduce dislocations around the crack tips. Dislocation segments cut out from loops were observed around the crack tip, the three-dimensional structure of which was characterized by using by electron tomography. Their Burgers vectors including the sings were also determined by oscillating contrasts along dislocations. In order to investigate the effect of the dislocations on fracture behaviours, local stress intensity factor due to one dislocation was calculated, which indicates the dislocations observed were shielding type to increase fracture toughness.

HVEM study of crack-tip dislocations in Si crystals prepared by FIB and twin-blade cutting method

Crack-tip dislocations in silicon crystals have been examined by using high-voltage electron microscopy. Cracks were introduced by the Vickers indentation method at room temperature and the indented specimens were annealed at high temperatures to induce dislocations around crack tips under the presence of residual stress due to the indentation. A selected area around a crack tip was thinned by a focused ion beam (FIB) technique. Specimens were thinned in advance by a twin-blade cutting (TBC) method, which is a simple cutting process for saving FIB machine time. A combination of FIB and TBC can be a useful thinning procedure for the efficient preparation of transmission electron microscopy specimens. Characteristic dislocation structures were observed around the tip of a crack, aiding the elucidation of dislocation processes, which is essential to increase the fracture toughness of materials.

HVEM characterization of crack tip dislocations in silicon crystals

Crack tip dislocations in silicon crystals have been studied using high voltage electron microscopy (HVEM). The dislocation images have been investigated by comparing the observed images to those that were simulated. Dislocation images were computed in the conditions g x b = 0, 1 or 2 (g: diffraction vector, b: Burgers vector). The characteristics of 60 degrees dislocations were examined in detail since these dislocations are not characterized only by the condition g x b = 0 criterion. The computed images were in good agreement with those observed by HVEM. Residual contrasts of 60 degrees dislocations under the condition g x b = 0 exhibited characteristic black-and-white contrasts, which can contribute to the characterization of the dislocations. Such characterization of dislocations is essential in order to clarify the dislocation mechanism which controls the fracture toughness of materials.

HVEM observation of crack tip dislocations in silicon crystals

Dislocation configurations near the tip of a crack in Si crystals has been investigated by using a high voltage electron microscope (HVEM). A ( 1 ̄ 10 ) crack was introduced into a (001) silicon wafer by using indentation method at room temperature, and the specimen was annealed at 823 K to emit dislocations from the tip of the crack under the presence of residual stress due to the indentation. An array of dislocations was seen not only in front of the crack tip but also in the crack wake. The dislocations were emitted on the ( 1 1 ̄ 1 ) plane which is oblique to the ( 1 ̄ 10 ) crack. The effect of crack tip shielding due to the dislocations is analyzed to be mainly mode I. Dense dislocation region is also found near the tip, suggesting the occurrence of dislocation multiplication around the crack tip.

Energy States of Deformation-Induced Dislocations in Silicon Crystals

Energy States of Deformation-Induced Dislocations in Silicon Crystals

Analysis of Oxygen Gettering and Dislocation Locking in Silicon

ABSTRACTThe motion under an applied stress of dislocations in silicon crystals is slowed and stopped by the presence of oxygen inthe material. A model is presented that quantitatively describes the inhibition of dislocation motion by accounting for the oxygen gettering to dislocations caused by diffusion and stress-enhanced migration. Drag on the dislocation motion ismodelled using the elastic interactions between the interstitial oxygen and the dislocation and the energy needed to breakbonds formed between silicon and aggregated oxygen atoms within the dislocation core. The predictions of the model agree quantitatively with the experimental data of Imai and Sumino.

Impurity Interactions with Dislocations in Silicon

ABSTRACTA review is presented of some aspects on the interactions of light element impurities with dislocations in silicon crystals on the basis of the works done by the author's group. Topics taken up are gettering of impurities by dislocations, electrical and optical activities of impurity atoms accumulated at the dislocation core, immobilization of dislocations due to impurity gettering, and the mechanism of strengthening of silicon wafers due to doping of impurities such as oxygen and nitrogen.

Temperature dependence of friction force acting on dislocations in silicon crystals

The characteristics of the dislocation motion in silicon crystals during annealing have been investigated by means ofin situ X-ray topographic observations in the temperature range from 1173 to 1273 K. When annealed at elevated temperatures, the small displacements in position of the dislocation segments took place so as to balance the friction force acting on these segments with the elastic interaction force between dislocations. From the analysis of (i) repulsive interaction between parallel screw dislocations with the same sign, and of (ii) configurational changes of dislocation half-loops, the friction force acting on dislocations can be determined at each annealing temperature by estimating the repulsive interaction force between parallel dislocations, and the force due to line tension for curved dislocation. On the basis of the analysis of the temperature dependence of friction force, the activation energy for dislocation motion is evaluated to be 2.4 eV for a screw dislocation and 2.2 eV for a 60° dislocation.

Temperature dependence of friction force acting on dislocations in silicon crystals

Temperature dependence of friction force acting on dislocations in silicon crystals

SCATTERING OF ELECTRONS BY SCREW DISLOCATIONS IN SILICON CRYSTALS

In this paper, the scattering of electrons by 〈110〉-screw dislocations insilicon crystals is discussed. We use the tight-binding approximation, only electrons in the s and p state are taken into account. With the long wave length approximation, only scattering of electrons near Г in the first BZ is considered. A scattering theoretical approach yields an integral equation of Kirchh off-Huygens type. The scatlering equation has been solved by means of gauge transformation and Green's function. It is confirmed that, as in the ease of single band in the case of many bands the shadow, which is the region that can not be affected by electron flux, appears in the down stream side of dislocations as well.

Interaction of Dislocations with Impurities and its Influence on the Mechanical Properties of Silicon Crystals

ABSTRACTA review is presented of the work on the influence of impurities on the dynamic behavior of dislocations in silicon crystals and also on the resulting effects in the mechanical strength performed by the author's group. Special emphasis is laid on the effects of light element impurities such as oxygen, nitrogen and carbon. Although all of these impurities do not affect the velocities of dislocations moving under relatively high stresses, oxygen and nitrogen atoms are found to lock slowly moving dislocations and dislocations at rest very effectively. Such locking of dislocations results in the decreases in the activities of generation and multiplication centers for dislocations, leading to the strengthening of the crystals. The high strength of silicon crystals brought about by the impurities is lost when the crystals are subjected to the heat treatments which allow the precipitation of the impurities on a macroscopic scale. This softening is shown to be caused by dislocations punched out from precipitates and by the exhaustion of the impurities dissolved in the matrix crystal.

In situ X-raytopographic studies of the generation and the multiplication processes of dislocations in silicon crystals at elevated temperatures

Abstract The generation of dislocations in silicon crystals at elevated temperatures and the processes by which they multiply have been investigated by in situ X-ray topographic observations utilizing a high-power X-ray generator and a PbO vidicon camera. Some dislocation structure was observed to develop through the crystal under stress before macroscopic deformation starts by means of the propagation of Lüders bands. The generation of dislocations from surface flaws and the influence of dissolved oxygen atoms on such a process were studied in detail, and interpretations of the observations are presented. Two mechanisms for the multiplication of dislocations during their motion are proposed on the basis of the observations.

High-Resolution Video Display of X-Ray Topographs with the Divergent Laue Method

An X-ray imaging device utilizing a high sensitivity image orthicon tube has been incorporated in the divergent Laue method of diffraction topography using a point source. An X-ray optical magnification of diffraction images has made it possible to obtain a spatial resolution better than that of the imaging device. Preliminary experiments have demonstrated that individual dislocations in silicon crystals can be displayed with a resolution of better than 25 µm.

X-ray topographic observation of moving dislocations in silicon crystals

An instantaneous display of topographic images of individual dislocations was made by the combination of a high-power x-ray generator and a television unit with an x-ray sensing PbO-Vidicon camera tube. Si wafers were deformed by tension (about 300 g/mm2) at about 1000 °C in a vacuum furnace, and, simultaneously, moving dislocations were observed continuously with the television unit. The observation of dislocations moving as fast as 0.3 mm/sec may indicate the possibility that this technique can be a powerful tool in investigating the dynamic properties of dislocations.