Formation Of Grown-in Defects Research Articles

Invited; Stress and Doping Impact on Intrinsic Point Defect Behavior in Growing Single Crystal Silicon

For the further development of 450 mm-diameter defect-free Si crystals, one has to take into account the impact of thermal stress on intrinsic point defect properties and behavior during single crystal growth from a melt. In this study, we evaluate the impact of thermal stress between -30 MPa (tensile) and 30 MPa (compressive), which probably covers the actual values in mass production for 450 mm-diameter crystals, on the so-called Voronkov criterion of dominant point defects.The dependence of the formation and migration enthalpies of vacancy V and self-interstitial I on the stress is evaluated by density functional theory (DFT). The obtained results are used to more accurately describe the impact of thermal stress on the critical (v/G)0. The impact of compressive thermal stress on (v/G)0 is predicted to shift the growing Si crystal more vacancy-rich, as recently confirmed experimentally by Nakamura et al (ECS Solid State Letters, 3 (2014) N5-N7). Furthermore, the dependence on the thermal stress of the process window for defect-free Si growth is clarified, which is important for the development of the pulling process of future large-diameter defect-free Si crystals.Also the mechanisms behind the experimentally observed impact of the type and concentration of substitutional dopants on intrinsic point defect behavior and formation of grown-in defects (voids and interstitial clusters) in a Si single crystal growing from a melt, are clarified. DFT calculations with 216-atom supercells are carried out to obtain the formation energies of V and I at all sites within a sphere around the dopant atom with 6 A radius for V and 5 A radius for I. P-type (B and Ga), neutral (C, Ge, and Sn) and n-type (P, As, Sb, and Bi) dopants are considered. The formation energies of V and I around dopant atoms change depending on the types and sizes of dopants. On the basis of the calculated results, an appropriate model of intrinsic point defect behavior in heavily doped Si is proposed. (1) The incorporated total V and I concentrations at the melting point depend on the types and concentrations of dopants. (2) Most of the total V and I concentrations contribute to Frenkel pair recombination during Si crystal growth at temperatures much higher than those to form grown-in intrinsic point defect clusters. The Voronkov model, while taking into account the present improvements, clearly explains all reported experimental results on grown-in defects for heavily doped Si.The proposed improved Voronkov model uniformly explains point defect behavior for all dopant types and concentrations, taking into account also thermal stress levels.

On the role of thermal gradient related stress in intrinsic defect formation during single crystal silicon growth from the melt

The incorporation of intrinsic point defects during silicon crystal growth from the melt is discussed using recent data for intrinsic point defect thermal equilibrium and diffusivity. It is shown that the impact of compressive stress on the thermal equilibrium concentration and diffusivity of vacancies and self-interstitials should be taken into account. An analytical expression is derived to quantify the relation between crystal diameter and the critical pull rate window to grow defect free crystals. The results are compared with published experimental data on grown-in defect formation for crystal diameters ranging from 1 to 40cm. It is shown that both the thermal stress due to the axial thermal gradient at the melt/solid interface and the silicon yield stress at high temperature play a crucial role. An empirical expression is proposed to describe the dependence of the thermal gradient on pulling rate.

Intrinsic point defect incorporation in silicon single crystals grown from a melt, revisited

The so-called Voronkov criterion states that the dominant intrinsic point defect in a silicon single crystal grown from a melt is determined by the ratio of pulling speed over temperature gradient near the melt/solid interface. Above a critical value of this ratio, the crystal is vacancy-rich, while for a ratio below this value, the crystal is interstitial-rich. Applying the Voronkov criterion implies, however, intrinsic point defect diffusivities and/or thermal equilibrium concentrations that can differ strongly from those experimentally determined using self- and metal-diffusion experiments. Furthermore, for a given hot zone, crystal diameter, and length, the thermal gradient itself at the melt/solid interface is a function of the pulling speed, so that the criterion in principle can be replaced by one for the thermal gradient only. There is also experimental evidence, based on crystal detaching experiments, that the growing crystal is always vacancy-rich at the solid/melt interface. In the present paper, the validity of the Voronkov criterion is critically reviewed and the impact of stress, in particular on intrinsic point defect thermal equilibrium concentrations, is taken into account and discussed. It is shown that the temperature and stress gradient near the melt-solid interface have an important impact on the intrinsic point defect incorporation and on the formation of grown-in defects that can be observed in the as-grown and thermally treated crystal. It is also likely that both types of intrinsic point defects can be present in supersaturation in different temperature windows during crystal pulling, leading to the observed coexistence of vacancy and self-interstitial clusters in the as-grown crystal. It is shown that, when taking into account stress effects, there is no need to assume intrinsic point defect diffusivities and thermal equilibrium concentrations that are different from those determined, e.g., from self- and metal-diffusion experiments and from ab initio calculations.

Formation of grown-in defects in molecular beam epitaxial Ga(In)NP: Effects of growth conditions and postgrowth treatments

Effects of growth conditions and post-growth treatments, such as presence of N ions, N2 flow, growth temperature, In alloying, and postgrowth rapid thermal annealing (RTA), on formation of grown-in defects in Ga(In)NP prepared by molecular beam epitaxy are studied in detail by the optically detected magnetic resonance (ODMR) technique. Several common residual defects, such as two Ga-interstitial defects (i.e., Gai-A and Gai-B) and two unidentified defects with a g factor around 2 (denoted by S1 and S2), are closely monitored. Bombardment of impinging N ions on grown sample surface is found to facilitate formation of these defects. Higher N2 flow is shown to have an even more profound effect than a higher number of ions in introducing these defects. Incorporation of a small amount of In (e.g., 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In; however, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai-related defects formed during the growth. In the alloys where the Gai-A and Gai-B defects are absent in the as-grown samples (i.e., GaNP grown at a low temperature of 460°C), the concentrations of the two Gai defects are found to increase after postgrowth RTA. This indicates that the defects originally introduced in the as-grown alloys have been transformed into the more thermally stable Gai-A and Gai-B during RTA. On the other hand, when the Gai-A and Gai-B are readily abundant (e.g., at higher growth temperatures (⩾500°C), RTA leads to a slight reduction of the Gai-A and Gai-B ODMR signals. The S2 defect is also shown to be thermally stable upon the RTA treatment.

Relating Microdefects to Growth Conditions in Czochralski Si Crystal Growth

The formation of grown-in defects in silicon crystals is controlled by the concentration of intrinsic point defects. Under steady-state conditions, the type of the prevailing point defect species is linked to the ratio of pull rate (v) and temperature gradient (G) in the crystal at the solidification front. It has been shown that this ratio as well as computed point defect distributions are in good agreement with experimental data. In this paper, we couple transient heat transfer with transient point defect models and show that the quasi-steady assumption and the v/G criteria are no longer valid if strong variations in the pulling velocity occur. Therefore, for a detailed understanding how defects are related to growth conditions, the thermal history should not be neglected.

Computer Simulation for Morphology, Size, and Density of Oxide Precipitates in CZ Silicon

A computer simulation model for oxygen precipitation during crystal growth and wafer annealing of Czochralski silicon is constructed. In this model, the precipitate morphology is determined by minimizing the excess free energy. This model is connected with the formation models of grown-in defects, such as crystal-originated particles (COPs) in the vacancy-rich region or extrinsic stacking faults in the self-interstitials rich region. That is, the simulation of oxygen precipitation starts at 1000 or 900°C with the input data of residual point defect concentrations after COP or stacking-fault formation. The model well simulates oxygen precipitation behavior. For example, the simulated results of isothermal annealing at 700 and 800°C show that the precipitate morphology is initially spherical, then changes to oblate spheroidal with an increase in annealing time, and the aspect ratio β is almost constant at for longer than 200 h. The simulated β agrees approximately with experimentally determined of platelet precipitates reported in the literature. The values of both the density and the growth rate of precipitates agree for the simulations and experiments. The model also shows that oxygen precipitation during crystal growth strongly depends on the residual point defect concentrations after grown-in defect formation. © 2003 The Electrochemical Society. All rights reserved.

Transient and quasi‐stationary simulation of heat and mass transfer in Czochralski silicon crystal growth

AbstractThe formation of grown‐in defects in silicon crystals is controlled by the concentration of intrinsic point defects. Under steady state conditions the type of the prevailing point defect species is linked to the ratio of pull rate and temperature gradient in the crystal at the solidification front. It has been shown that this ratio as well as computed point defect distributions are in good agreement with experimental data. In this paper we compare a coupled transient heat transfer and transient point defect transport model with quasi steady state simulations at various time steps. Both simulations show the same qualitative results, quantitative differences in temperature are less than 1 %. But already for constant pull rates the defect distributions show qualitative differences between transient and quasi steady state simulations. Therefore, for a detailed understanding how defects are related to growth conditions, the thermal history should not be neglected.

Nitrogen effect on gold diffusion in Cz Si

Gold diffusion in Czochralski grown (Cz) Si with and without nitrogen, introduced during growth, has been studied. It is found that the Au concentration in substitutional positions after diffusion at 700°C, 750°C and 800°C in Cz Si doped with nitrogen is always less than that in usual Cz Si. A decrease of the substitutional Au concentration in nitrogen doped crystals can be explained under the assumptions that nitrogen or nitrogen-related centers stimulates oxygen precipitation and suppresses the grown-in defect formation.

Modeling of transient point defect dynamics in Czochralski silicon crystals

Intrinsic point defects control the formation of grown-in defects in silicon crystals. Under steady state conditions, the type of the prevailing point defect species is exclusively determined by the ratio of pull rate and temperature gradient in the crystal at the interface. In this study, simulations have been performed for transient growing processes where the pulling rate has been abruptly changed. Large reservoirs of interstitials are formed in fast-grown, vacancy-rich crystals near the interface after abruptly reducing the pulling rate for 30 min. During further growth at high pull rate, these interstitial reservoirs are transformed into large ellipsoidal defect patterns. Experimental results are excellently reproduced if equilibrium concentrations are used as boundary conditions for interstitials and vacancies at all crystal surfaces.

Formation of Grown-in Defects during Czochralski Silicon Crystal Growth

The formation behavior of grown-in defects in Czochralski silicon (CZ-Si) crystals was investigated using two crystals that were quenched during growth but in one case after crystal growth had been halted for 5 h. The distributions of grown-in defect density and size, and their micro-structures were analyzed as a function of temperature during crystal growth just before quenching by means of an optical precipitate profiler (OPP) and an atomic force microscope (AFM) coupled with a laser particle counter. The formation of grown-in defects, which are considered to be octahedral voids, was found to consist of two dominant processes. The first step involves rapid void growth in a narrow temperature range of about 30° C below 1100° C and the subsequent step consists of an oxide film growth on the inner surface of the void during the cooling process to about 900° C after void formation. It was also found that the growth of the oxide film in the voids is rate-limited by the diffusion rate of oxygen atoms in silicon. In addition, it is strongly suggested that void formation in such a narrow temperature range is due to a rapid agglomeration of vacancies.

Formation process of grown-in defects in Czochralski grown silicon crystals

We have determined the set of the diffusion coefficients ( D v: vacancies, D i: self-interstitials) and equilibrium concentrations ( C eq v: vacancies, C eq i: self-interstitials) of point defects which has been satisfied with the dependence of two-dimensional defect patterns on V and G (V: growth rate, G: axial temperature gradient) and with the reported product values of D v C eq v and D i C eq i. Recently, it has been reported by direct TEM (Transmission Electron Microscopy) observation that the grown-in defects in the vacancy dominant region are the voids of octahedral shape. The idea that the grown-in defects are the voids formed by the vacancy aggregation has been examined by the simulation model. It is shown that this model can well describe the behaviors of grown-in defect formation during the crystal growth and that it is possible to form the void as the grown-in defect in CZ silicon crystals.

Formation of Grown-in Defects in CZ-Si Crystals

Formation of Grown-in Defects in CZ-Si Crystals

Formation of grown-in defects during the growth of single silicon crystals and their effects on electrical characteristics

Formation of grown-in defects during the growth of single silicon crystals and their effects on electrical characteristics

Influence of the thermal history of melts on the formation of grown-in defects in silicon

We have investigated the influence of time-dependent changes of melt properties on the formation of grown-in defects in silicon single crystals grown by the Czochralski method. It is found that the density of grown-in defects increases if the crystal is pulled immediately after melting. The results indicate that the change in the state of melts can influence the formation of grown-in defects in silicon single crystals.

Characterization Of Grown-In Defects In CZ-SI Crystals By Bright Field IR Laser Interferometer

AbstractWe have developed a quantitative measurement method for the number density, size and morphology of grown-in defects in czochralski-grown silicon (CZ-Si) crystals with a bright-field infrared-laser interferometer (known as Oxygen Precipitate Profiler; OPP). Using this method we investigated the effect of crystal cooling condition during crystal growth on the formation of grown-in defects by growth holding experiments. The relation between gate oxide integrity (GOI) and grown-in defects was studied. It was revealed that the grown-in defects have octahedral shape and degrade the GOI performance. We estimate the density as well as cumulative volume of the grown-in defects and discuss the formation mechanism of them.

Influence of hydrogen and oxygen on the melt properties and the crystal growth in silicon

The influence of hydrogen and oxygen on the density of the silicon melt has been studied. The density of the oxygen-containing melt is identical with that without oxygen and shows an anomalous increase of the density near the melting point. The melt density in an argon gas ambient mixed with 7.15% hydrogen is equivalent to that in a pure argon gas at the melting temperature, but showed greater values at higher temperatures (1430–1500 °C). The density of the silicon melt at 1430 °C increases over 5 h after completion of melting. We found that such time-dependent change of the melt properties influences the formation of grown-in defects during crystal growth.

Characterization of ZnWO 4: Fe single crystals by optical and scanning electron microscopic methods

The effect of iron dopant incorporation and certain transient growth processes on the defect formation in Czochralski-grown ZnWO 4 single crystals were studied by using optical and scanning electron microscopic imaging methods as well as energy dispersive X-ray and cathodoluminescence spectroscopies. It was found that, the iron dopants in the crystals decrease the luminescence intensities, increase the half-widths of the emission bands and produce secondary peaks at 460, 515, 530 and 565 nm besides the intrinsic one detected between 480 and 503 nm at different sample temperatures. In the grown-in defect formation the Fe dopant seems to play only a minor role. The iron segregation was detected only on microdefects and at high dopant concentrations.

The Formation of Defects Degrading Gate Oxide Integrity During CZ-Si Crystal Growth

AbstractThe formation of grown-in defects degrading the gate oxide integrity (GOI) has been studied. The growth-halting experiments were carried out to investigate the temperature ranges at which the formation of the defects was promoted or suppressed. GOI is improved in the crystal regions slowly cooled above 1330°C and between 1060°C and 1100°C. It is degraded in the crystal regions held below 1060°C. In the peripheral of the crystals, those temperature ranges are about 30°C lower. The defects are formed and grown below 1060°C in the center part of the crystal. The defect density is decreased with cooling time between 1060°C and 1100°C. These phenomena are considered to be closely related with reactions of intrinsic point defects, that is, the pair annihilation or the aggregation. The temperatures at which the pair annihilation and the aggregation of the point defects occur are dependent upon the supersaturation of the point defects.