Efficiency of the formation of radiation defects in heat-treated dislocation-free zone n-silicon

A study was made of processes involved in the formation of radiation defects (RD) in n-type dislocation-free silicon subjected to high-temperature heat treatment at T_t = 600–1300°C. It was established that the effectiveness of introducing compensating RDs changes significantly with an increase in T_t. It is proposed that interstitital inclusions present in the crystal are transformed during heat treatment, these inclusions creating strain fields around themselves and thus influencing the efficiency with which radiation defects are formed.A. N. Sevchenko Scientific Research Institute of Applied Physical Problems. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 93–95, November, 1993.     

Simulation of the stresses produced in large-diameter silicon wafers during thermal annealing

The three-dimensional problem of stress and strain fields in dislocation-free silicon wafers 200 and 300 mm in diameter placed horizontally on three symmetrical supports and subjected to is gravitational forces and thermal stresses formulated and solved in the isotropic approximation. Under the action of gravitational forces, a wafer is shown to have the lowest total stress when the supports are positioned at a distance of 0.6–0.7R from the center of the wafer. The shear-stress fields are calculated for all possible slip systems. The elastic-stress field in a 300-mm wafer is found to be induced mainly by gravitational forces even at a radial temperature gradient of 10 K. At this temperature gradient, the contribution from thermal stresses in a 200-mm wafer is comparable to the contribution from gravitational forces. At radial temperature gradients lower than 5 K, the contribution from thermal stresses can also be neglected for a 200-mm wafer. The maximum shear stresses calculated indicate that one should not neglect possible dislocation generation in the zone of contact between a wafer and the supports during high-temperature annealing of 200-mm and, especially, 300-mm wafers.     

Dynamic properties of dislocations in silicon wafers heat-treated at low temperatures

The specific features of the dislocation motion in dislocation-free silicon wafers (single crystals are grown by the Czochralski method) heat-treated at 450 and 650°C have been investigated. It is found that the low-temperature treatment of silicon wafers with an oxygen content of (7–8)×10¹⁷ cm^?3 substantially affects the dynamic properties of dislocations generated into silicon wafers during their four-point bending and brings about an increase in the starting stresses of the onset of the dislocation motion. A characteristic spatial inhomogeneity is observed in the generation and propagation of dislocations from indentations upon the bending of heat-treated wafers. The reasons for the regularities revealed are discussed.     

Specific features in the generation and motion of dislocations in heat-treated silicon wafers

The specific features in the generation and motion of dislocations in silicon single-crystal wafers after different heat treatments are investigated by the four-point bending technique. It is demonstrated that annealing of silicon single-crystal wafers at a temperature of 450°C leads to their substantial hardening as compared to the postgrowth state. The oxygen-containing precipitates and precipitate dislocation pileups formed in the silicon wafer bulk during multistage heat treatment are efficient heterogeneous nucleation sites of dislocations under the action of thermal or mechanical stresses. It is found that the multistage heat treatment of the silicon wafers under conditions providing the formation of an internal getter within their bulk results in considerable disordering of the wafer structure. The inference is made that the formation of the defect state in the crystal lattice of silicon and the strength characteristics of silicon wafers substantially depend on the temperature-time schedules of the low-temperature stage of multistage heat treatment.     

Dislocation generation in heat-treated nitrogen-doped silicon wafers when applying external loads

The features of generation and motion of dislocations in nitrogen-doped dislocation-free silicon wafers after their multistage thermal treatments are investigated. It is established that doping with nitrogen leads to a substantial increase in stresses of the onset of plastic deformation from the external and internal heterogeneous sources in heat-treated wafers. The motion velocity of dislocations in nitrogen-doped silicon wafers is lower than in undoped wafers. The strengthening effect of nitrogen is apparently caused by its activating effect on the decomposition process of a supersaturated solid solution of oxygen during heat treatment.     

Diffuse x-ray scattering from self-interstitials in zinc

Diffusex-ray scattering in the region between the Bragg peaks has been calculated for self-interstitials in zinc. The required lattice distortions are calculated by the Kanzaki method and the scattering contributions from all equivalent orientations of a defect configuration are averaged. It is shown that a measurement in the (110) plane can clearly establish the stable interstitial configuration.     

High-resolution study of x-ray resonant Raman scattering at the K edge of silicon

We report on the first high-resolution measurements of the K x-ray resonant Raman scattering (RRS) in Si. The measured x-ray RRS spectra, interpreted using the Kramers-Heisenberg approach, revealed spectral features corresponding to electronic excitations to the conduction and valence bands in silicon. The total cross sections for the x-ray RRS at the 1s absorption edge and the 1s-3p excitation were derived. The Kramers-Heisenberg formalism was found to reproduce quite well the x-ray RRS spectra, which is of prime importance for applications of the total-reflection x-ray fluorescence technique.     

On the generation of bulk microdefects in phosphorus-diffused monocrystalline silicon solar wafers after a high-thermal treatment studied by X-ray topography

Oxygen is the most important impurity in free dislocation Czochralski silicon single crystals incorporated interstitially during the growth. The knowledge of oxygen behavior after thermal processes is of great technological importance, since different kinds of bulk microdefects such us SiO₂ precipitates, dislocation loops and stacking faults can be generated. In monocrystalline silicon solar cell manufacturing fabrication, there are several high-thermal treatments. The first is the diffusion process at 850–900 °C. Three different kinds of phosphorus diffusion wafers, standard PO₃Cl liquid, spray-on and screen printing, were comparatively studied by X-ray topography showing that phosphorus diffusion improves the crystal quality by a gettering process whose best efficiency is in PO₃Cl-diffused wafers. Later, another fabrication high-thermal step is for instance the rear surface passivation taking place at temperatures from 800 to 1,050 °C. For this reason, it is important to study how a high-thermal treatment at 1,000 °C affects the different phosphorus-diffused wafers mentioned above. To evaluate and characterize the possible defects induced by the oxygen precipitation, X-ray topography has been employed. Results show that annealed wafers are not perfect crystals; the oxygen precipitation induces the generation of bulk microdefects whose kind, size and density depend on the diffusion method employed. In PO₃Cl and spray-on diffused wafers, retardation in the oxygen precipitation process takes place after annealing, while in screen printing this process is recovered and a kind of mixed defects between dislocation loops and platelet precipitates is generated.     

Diffuse x-ray scattering in the Hg2I2 model incipient ferroelastics

This paper reports the first detection and study of diffuse maxima in x-ray scattering in Hg₂I₂ incipient ferroelastics. These maxima originate from the formation of clusters of the incipient orthorhombic phase in the paraelastic tetragonal matrix. The nucleation and growth of the clusters are caused by spatial and temporal fluctuations of the order parameter (which correspond to the TA soft mode at the X point of the Brillouin zone edge) and are induced by the incipient phase transition. Information is obtained on the temperature behavior of the susceptibility and correlation length and on the shape and anisotropy of clusters, and the critical indices are determined.     

Kinetics of formation of vacancy microvoids and interstitial dislocation loops in dislocation-free silicon single crystals

The formation of vacancy microvoids and A-microdefects has been calculated according to the model of point defect dynamics in the absence of recombination of intrinsic point defects at high temperatures. It has been assumed that this solution is possible in the case where the precipitation of impurities begins in the vicinity of the crystallization front. It has been demonstrated that the formation of vacancy microvoids has a homogeneous nature and that the interstitial dislocation loops are predominantly formed through the deformation mechanism.     

Direct bonding of silicon wafers with the concurrent formation of diffusion layers

An original technique for Si-Si direct bonding combined with impurity diffusion in a single process is suggested. A dopant (aluminum) source is located at the interface. The high-temperature treatment of the polished wafers in an oxidizing atmosphere results in the diffusion of Al atoms and the formation of a p-n junction in n-silicon. The presence of aluminum is shown to improve the continuity of the interface. Results obtained are explained within a model whereby the initial contact between the hydrophilic silicon surfaces in a water solution of aluminum nitrate Al(NO₃)₃ serves to increase the bonding area of the wafers at room temperature due to the interaction of Al-OH groups with water molecules adsorbed on the surfaces of the wafers.     

Kinetics of high-temperature precipitation in dislocation-free silicon single crystals

The defect structure of dislocation-free silicon single crystals has been calculated using the approximate solution of the Fokker-Planck partial differential equations. It has been demonstrated that the precipitation starts to occur near the crystallization front due to the disappearance of excess intrinsic point defects on sinks whose role is played by oxygen and carbon impurities.     

Diffuse x-ray scattering near Bragg peaks from point defects in a general lattice

Using the continuum theory of linear elasticity, diffuse x-ray scattering has been calculated in the immediate neighbourhood of Bragg peaks from point defects in a lattice containing more than one atom in the unit cell. General expressions are obtained for the Debye-Waller factor, Huang diffuse scattering and the asymmetric scattering due to the defect. For lattices with one atom per unit cell, these expressions reduce to the well-known formulae of diffuse scattering.     

Persistence of covalent bonding in liquid silicon probed by inelastic x-ray scattering

Metallic liquid silicon at 1787 K is investigated using x-ray Compton scattering. An excellent agreement is found between the measurements and the corresponding Car-Parrinello molecular dynamics simulations. Our results show persistence of covalent bonding in liquid silicon and provide support for the occurrence of theoretically predicted liquid-liquid phase transition in supercooled liquid states. The population of covalent bond pairs in liquid silicon is estimated to be 17% via a maximally localized Wannier function analysis. Compton scattering is shown to be a sensitive probe of bonding effects in the liquid state.     

On the recombination of intrinsic point defects in dislocation-free silicon single crystals

The recombination of intrinsic point defects in dislocation-free silicon single crystals is investigated. It is established experimentally and confirmed by thermodynamic calculations that this process in the vicinity of the crystallization front is hindered by the recombination barrier. The recombination parameters (such as the recombination barrier height, the recombination time, and the recombination factor) for the model describing the dynamics of point defects at low and high temperatures are evaluated in terms of the heterogeneous mechanism of nucleation and transformation of grown-in microdefects. It is confirmed that the decomposition of a supersaturated solid solution of point defects can occur according to two mechanisms, namely, the vacancy and interstitial mechanisms. Vacancies and intrinsic interstitial silicon atoms find sinks in the form of oxygen and carbon background impurities. It is demonstrated that the formation of “intrinsic-point-defect-impurity” pairs is a dominant process in the vicinity of the melting temperature.     

Defect cores investigated by x-ray scattering close to forbidden reflections in silicon

A new x-ray scattering method is presented making possible the detection of defects and the investigation of the structure of their cores. The method uses diffuse x-ray scattering measured close to a forbidden diffraction peak, in which the intensity scattered from the distorted crystal lattice around the defects is minimized. As a first example of this nondestructive method we demonstrate how the local compression of the extra {111} double planes in extrinsic stacking faults in Si can be probed and quantified using a continuum approach for the simulation of the displacements. The results of the theory developed are found to be in very good agreement with atomistic simulations and experiments.     

High-pressure study of x-ray diffuse scattering in ferroelectric perovskites

We present a high-pressure x-ray diffuse scattering study of the ABO3 ferroelectric perovskites BaTiO3 and KNbO3. The well-known diffuse lines are observed in all the phases studied. In KNbO3, we show that the lines are present up to 21.8 GPa, with constant width and a slightly decreasing intensity. At variance, the intensity of the diffuse lines observed in the cubic phase of BaTiO3 linearly decreases to zero at approximately 11 GPa. These results are discussed with respect to x-ray absorption measurements, which leads to the conclusion that the diffuse lines are only observed when the B atom is off the center of the oxygen tetrahedron. The role of such disorder on the ferroelectric instability of perovskites is discussed.