Czochralski-grown Silicon Crystals Research Articles

Shallow thermal donors in nitrogen-doped silicon single crystals

Czochralski-grown nitrogen-doped silicon crystals contain shallow thermal donors (STD) which are not present in reference crystals. In the course of annealing at 600 or 650°C, the STD concentration reaches saturation and this concentration scales with nitrogen content N as N1/2. This implies that an STD includes only one nitrogen atom and that the most likely model of the STD defect is the NOm complex of an interstitial nitrogen atom with m oxygen atoms. The number m is estimated as, on the average, m=3 from data on the temperature dependence of the equilibrium constant for the complex formation reaction

Interaction between self-interstitials and the oxygen dimer in silicon

Interactions between the oxygen dimer (O 2i) and silicon self-interstitials (I) and vacancies (V) have been studied in Czochralski-grown silicon (Cz–Si) crystals using infrared absorption and deep level transient spectroscopies. The focus in this report is on reactions of O 2i with I. The first step in this interaction is found to be the formation of a self-interstitial-dioxygen centre (IO 2i) with oxygen-related local vibrational mode (LVM) bands at 922 and 1037 cm −1. During the second formation step, another centre, I 2O 2i, with LVM bands at 918 and 1034 cm −1 is suggested to appear. A Si-related band at about 545 cm −1 is also assigned to both the IO 2i and I 2O 2i centres. The IO 2i centre is found to be electrically active with an acceptor level at E c−0.11 eV. The both defects, IO 2i and I 2O 2i, are stable at room temperature and anneal out at about 400 and 550 K, respectively.

Nature of large-scale oscillations in oxygen concentration along the growth axis in Czochralski-grown silicon crystals

Oxygen distribution in a Si crystal (100 mm in diameter) has been studied by the absorption method in the range of the absorption band of interstitial oxygen, λ = 5.81 μm. Large-scale fluctuations (∼1 cm) of the oxygen concentration (N 0) along the growth axis were determined. Depending on the melt height, the regions of the chaotic and quasiperiodic changes were established, as well as the region of the constant N 0 value, and their relation to turbulent, quasiperiodic, and stationary modes of melt convection in crystallization. The values of the critical Rayleigh number for the melt transition from stationary to quasiperiodic (3 × 103) and from quasiperiodic to turbulent (1.7 × 104) convection modes are determined for growth of silicon crystals by the Czochralski method. The dominating modes of N 0 concentration oscillations at two incommensurable frequencies, f 1 = 1.3 × 10−3 and f 2 = 6 × 10−4 Hz, are assumed to be related to the oscillatory transfer of oxygen from the walls of the quartz crucible to the crystallization front and restructurization of the convective flow pattern of the melt in the course of crystal growth.

Oxygen precipitation in nitrogen-doped Czochralski-grown silicon crystals

Oxygen precipitate behavior of nitrogen-doped Czochralski-grown silicon (CZ-Si) crystals is investigated. It is found that nitrogen doping enhances oxygen precipitation after heat treatment. The oxygen precipitate volume density in nitrogen-doped crystals after heat treatment does not change regardless of the heat treatment temperature, while the oxygen precipitate volume density of crystals which are not nitrogen doped decreases as the heat-treatment temperature increases. The characteristics of precipitation behavior in nitrogen-doped CZ-Si crystals are due to the “grown-in” oxygen precipitates, which already exist in an as-grown state with a high volume density. The oxygen precipitation growth of nitrogen-doped crystals is found to be an oxygen diffusion limited process, the same as in the case of the oxygen precipitation growth of crystals which are not nitrogen doped. The formation mechanism of grown-in oxygen precipitates will also be discussed in this article.

Numerical analysis for the dynamics of the oxidation-induced stacking fault in czochralski-grown silicon crystals

The continuum model of point defect dynamics to predict the concentration of interstitial and vacancy is established by estimating expressions for the thermophysical properties of point defects and the point defect distribution in a silicon crystal and the position of oxidation-induced stacking fault ring (R-OiSF) created during the cooling of crystals in Czochralski silicon growth process are calculated by using the finite element analysis. Temperature distributions in the silicon crystal in an industrial Czochralski growth configuration are measured and compared with finite volume simulation results. These temperature fields obtained from finite volume analysis are used as input data for the calculation of point defect distribution and R-OiSF position. Calculations of continuum point defect distributions predict the transition between vacancy and interstitial dominated precipitations of microdefects as a function of crystal pull rate (V). The dependence of the radius of R-OiSF (ROiSF) on the crystal length with fixed growth rate for a given hot zone configuration is examined. The ROiSF is increased with the increase of crystal length. These predictions from point defect dynamics are well agreed with experiments and empirical V/G correlation qualitatively, where G. is the axial temperature gradient at the melt/crystal interface.

Hydrogen-plasma-enhanced oxygen precipitation in silicon

Czochralski-grown silicon crystals with different carbon concentrations havebeen heat-treated in µ-wave hydrogen plasma in the temperature range500-700 °C. For comparison, control samples have been treated in afurnace in a nitrogen ambient. Infrared (IR) absorption measurements show thatthe loss of oxygen atoms from solution due to the formation of SiO2precipitates is strongly enhanced by the H-plasma treatment in bothcarbon-lean and carbon-rich Si crystals. The loss of oxygen is accompanied bythe loss of substitutional carbon atoms from solution in the C-rich samples.The frequencies and shapes of the IR absorption bands associated with theprecipitates are different in C-rich and C-lean crystals, indicating theformation of different types of precipitate particle. The former bands (Crich) are similar following heat treatments in a H-plasma or in N2 gas. Itis inferred that a fast diffusing species penetrates into Si crystals duringthe H-plasma treatment, leading to a catalytic enhancement of oxygen diffusionthat in turn leads to enhanced precipitation. Possible mechanisms for theenhanced oxygen diffusion and precipitation are discussed briefly.

Electron spin resonance centers associated with oxygen precipitates in Czochralski silicon crystals

We have previously concluded that the oxygen-precipitate-associated defects that we identified by the deep levels at Ev+0.30 eV and Ec−0.25 eV were the Pb centers generated in the interface between the oxygen precipitates and the surrounding silicon crystal lattice [M. Koizuka and H. Yamada-Kaneta, J. Appl. Phys. 84, 4255 (1998)]. In order to confirm this conclusion, we have made electron spin resonance (ESR) measurements on the Czochralski-grown silicon crystals containing the oxygen precipitates generated by the two-step anneals of 500 °C, 20 h+700 °C, 60 h. We have found the ESR lines whose g values well coincide with those of the Pb0 and Pb1 centers. Thus it has been clarified that the Pb0 and Pb1 centers are generated by the oxygen precipitation as well as by the thermal oxidation. The present successful application of the ESR method to the annealed silicon crystals suggests that it can be a useful tool to characterize the precipitation state of the oxygen in silicon.

Observation and theory of theV−O−H2complex in silicon

The interaction of hydrogen with radiation-induced defects (RD's) in Czochralski-grown silicon crystals has been studied by infrared-absorption spectroscopy and ab initio modeling. Hydrogen and/or deuterium was introduced into the crystals by indiffusion from ${\mathrm{H}}_{2}$ $({\mathrm{D}}_{2})$ gas at $1200--1300\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The samples were subsequently irradiated with fast electrons $(E=2\ensuremath{-}4 \mathrm{MeV})$ and annealed in the temperature range of $100--600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The centers produced by the irradiation were the same in both the untreated and treated cases, namely the A-center, ${\mathrm{C}}_{i}\ensuremath{-}{\mathrm{O}}_{i}$ complex, and divacancy. A heat treatment of the H-treated samples resulted in the enhanced loss of these centers and the formation of centers containing hydrogen. The disappearance of the A centers in the temperature range of $100--150\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is correlated with the appearance of three local vibrational modes (LVM's) at 943.5, 2126.4, and $2151.5 {\mathrm{cm}}^{\ensuremath{-}1}.$ The isotopic shifts of these lines were obtained from measurements on the samples doped with hydrogen and deuterium. The lines are identified as related to stretching vibrational modes of a complex that consists of one oxygen and two hydrogen atoms sharing a vacancy site $(V\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{H}}_{2}$ complex). Ab initio calculations are used to explore the structures and properties of this defect. The origin of other LVM bands, which were observed upon annealing, is discussed.

Use of electron irradiation in studying thermal donors in silicon by the EPR method

The bistable thermal donors in Czochralski-grown silicon crystals were investigated by EPR spectroscopy and IR-absorption techniques. It is shown that using heat treatment at a temperature ≤400°C and appropriate conductivity compensation by irradiation with 3.5 MeV electrons, one can select from the total signal the EPR-signal associated with only one type, namely TDD2, of the thermal donors. Based on the model of a two-center core structure of the given complexes, an explanation of the EPR-spectroscopy data on the oxygen thermal donors in silicon is suggested.

Local vibrational mode bands of V–O–H complexes in silicon

H2 molecules, which are introduced into moderately doped silicon crystals by high-temperature in-diffusion from H2 gas ambient followed by fast cooling to room temperature, are found to interact effectively with the defects induced by irradiation of the crystals with fast electrons. In Czochralski-grown silicon crystals, the interaction of the mobile H2 molecules with vacancy-oxygen defects (A centers) leads to the creation of V–O–H2 complexes. This complex gives rise to infrared (IR) absorption lines at 943.5, 2126.4, and 2151.5cm−1. Ab initio calculations showed that the most stable configuration of V–O–H2 consists of one oxygen and two hydrogen atoms sharing a vacancy site. It is suggested that the interaction of the V–O–H2 complexes with interstitial oxygen atoms results in the formation of V–O2–H2 complexes, which are responsible for the IR absorption line at 891.5cm−1.

Magnetic-field induced generation of A-like centers in Cz-Si crystals

The effect of the constant magnetic-field induced generation of oxygen–vacancy defects in Czochralski-grown silicon crystals was detected for the first time. The qualitative theory of the effect is given. It assumes that the effect arises from excitation of the Si–O bond of interstitial oxygen and is valid for both constant and pulsed magnetic fields. Experimental verification of the theory in the combined constant and pulsed fields strongly confirmed it.

Influence of hydrostatic pressure at the temperatures about 1500 K on defect structure of Czochralski silicon

Abstract The averaged values of radii r and concentration n of microdefects which are the SiOx precipitates surrounded by dislocation loops were determined from the measured X-ray integral reflectivities of Czochralski grown silicon crystals subjected to annealing at high hydrostatic pressure (107–109 Pa) as well as from analysis of differential diffuse scattering behaviour near the Bragg angle. The values of these parameters and the Debye–Waller static factor behaviour show that process of the SiOx dissolution which usually takes place at the temperatures about 1500 K is slowed down in condition of hydrostatic pressure as comparing with treatment of such samples about 1500 K but by atmospheric pressure (P=105 Pa).

Local vibrational mode bands due to a DX-like hydrogen-related center in silicon

An absorption line at 1025.5 cm−1 has been observed in hydrogenated Czochralski-grown silicon crystals after irradiation with fast electrons and following annealing in the temperature range of 300–400 °C. The line was found to be related to a local vibrational mode (LVM) due to a DX-like hydrogen-related center, having a shallow donor and a deep acceptor electronic level. This LVM band was observed when the center was in the singly negatively charged state. Transformation of the defect into the neutral charge state due to photoionization resulted in disappearance of the LVM line and the appearance of several absorption lines in the range of 250–325 cm−1. These lines were interpreted earlier to be associated with ground-to-excited-state electronic transitions in an effective-mass-like shallow donor state of the center. Substitution of hydrogen by deuterium resulted in a shift of the LVM band to 1027.9 cm−1 that unambiguously indicates hydrogen incorporation into the defect. The structure of the center which gives rise to the observed absorption bands is discussed.

Hydrogen–oxygen interaction in silicon at around 50 °C

Formation kinetics of oxygen–hydrogen (O–H) complexes which give rise to an infrared absorption line at 1075.1 cm−1 have been studied in Czochralski-grown silicon crystals in the temperature range of 30–150 °C. Hydrogen was incorporated into the crystals by high temperature (1200 °C) in diffusion from H2 gas. It was found that the observed kinetics can be explained as being due to an interaction of mobile neutral hydrogen-related species with bond-centered oxygen atoms. The binding energy of the O–H complex was determined to be 0.28±0.02 eV. An activation energy for migration of hydrogen-related species responsible for the formation of the O–H complexes was found to be 0.78±0.05 eV. It was shown that atomic hydrogen and H2*, a complex containing two hydrogen atoms, one at bond-centered site and another one at antibonding site, cannot account for the hydrogen–oxygen interaction considered. Hydrogen molecules (H2) located at tetrahedral interstitial site are suggested to be the species which interact with interstitial oxygen atoms and form the complex giving rise to the absorption line at 1075.1 cm−1.

The effects of argon gas flow rate and furnace pressure on oxygen concentration in Czochralski-grown silicon crystals

The effects of argon gas flow rate and furnace pressure on oxygen concentration in Czochralski (CZ) grown silicon crystals were examined through experimental crystal growth. A newly designed gas controller was used for this study. Increase in the oxygen concentration with an increase in argon gas flow rate or with a decrease in furnace pressure was demonstrated for the first time. The results of oxygen concentration changes were analyzed in terms of calculated velocity of argon gas flow along the gas controller over the silicon melt surface. The flow velocity of argon gas was affected both by the argon gas flow rate and the furnace pressure. The flow velocity of argon gas was found to increase with an increase in argon gas flow rate under a fixed furnace pressure or with a decrease in furnace pressure under a fixed argon gas flow rate. The oxygen concentration in the CZ silicon crystals was found to be proportional to the flow velocity of argon gas. Two possible mechanisms which could explain this relationship were discussed.

Hydrogen-oxygen-vacancy complexes in Czochralski-grown silicon crystal

We studied the process of generation and some properties of shallow donors generated by annealing a hydrogen-doped Czochralski-grown silicon crystal after electron irradiation. Hydrogen was doped by annealing specimens at 1200 °C in hydrogen atmosphere followed by quenching. Specimens were irradiated with 3 MeV electrons. Three kinds of shallow donors, termed D1–D3, were generated and annihilated due to isochronal annealing between 300 and 650 °C as shown by the measurement of optical absorption at 6 K. The generation process of D1 was well described by the first order reaction. The activation energy for the generation of D1 was about 1.8 eV. This agreed well with the migration energy of a vacancy-oxygen pair (VO pair). Hence, it is proposed that D1 is a complex of one VO pair and a hydrogen aggregate. Neutral D1 is in a metastable state. The optical threshold energy for the excitation of the neutral charge state of D1 was about 0.36 eV. The energy barrier from the neutral to the stable state of D1 was estimated to be about 0.13 eV.

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.

Diffuse x-ray scattering from thermal donors in Czochralski-grown silicon

The diffuse x-ray (Cu $K{\ensuremath{\alpha}}_{1})$ scattering from Czochralski-grown (Cz) silicon crystals after annealing at 450 \ifmmode^\circ\else\textdegree\fi{}C for 24 h has been investigated. The x-ray measurements have been made near the (400) and (31\ifmmode\bar\else\textasciimacron\fi{}1) Bragg reflections in directions parallel and perpendicular to the scattering vector. All the characteristic features have been predicted by the theory for scattering from defect clusters with weak displacement fields (Huang scattering). It is shown that the long-range part of their displacement fields has an orthorhombic symmetry and the defects are the interstitial type. Furthermore, by comparing the symmetry of the diffuse scattering intensities with that of displacement fields around the thermal donor models in Cz Si, it is found that an NL8 or $I{\mathrm{O}}_{2}$ (self-interstitial and two oxygens) model is reasonable as a core structure of thermal donors.

The dissolution behavior of the void defects by hydrogen annealing in Czochralski grown silicon crystals

The annihilation of grown-in defects by hydrogen annealing have been explained as the dissolution of oxygen precipitates, because it has been generally thought that grown-in defects in Czochralski silicon crystals are gigantic oxygen precipitates. However, it is necessary to re-examine the mechanism of the annihilation of the defects by hydrogen annealing, because recently it has been shown that the grown-in defects were voids of octahedral shape. In this letter, a simulation model is presented which describes the annihilation process of void defects by hydrogen annealing.

Structural Perfection of Czochralski Grown Silicon Crystals Annealed above 1500 K under Hydrostatic Pressure

The structural perfection of Czochralski grown silicon crystals annealed at 1580-1620 K under hydrostatic pressure up to 10 9 Pa was investigated by X-ray diffractometry and topography supplemented by the method of absorption of infrared rays. Such treatment suppresses dissolution of oxygen-related defects. From the static Debye—Waller factor dependence on the reflection order it was concluded that large clusters or dislocation loops are the dominant type of defects for most of the samples. PACS numbers: 81.05.Cy, 81.40.—z