Czochralski Silicon Crystals Research Articles

Enhanced oxygen precipitation in neutron-irradiated nitrogen-doped Czochralski silicon crystal

Nitrogen and vacancies were intentionally introduced into Czochralski silicon crystal by doping and neutron irradiation, respectively, to study the effect on oxygen precipitation. A series of isochronal anneals in the temperature range of 700–1150 °C revealed that vacancies showed the prominent enhancement effect on oxygen precipitation at temperatures below 1000 °C, whereas nitrogen exhibited the evident enhancement in oxygen precipitation at temperatures above 900 °C. It is suggested that the vacancies induced by neutron irradiation form VnOm (n, m≥1) complexes acting as nuclei to facilitate oxygen precipitation in silicon. However, the VnOm complexes are not stable at higher temperatures; thus, the enhancement effect of vacancies on oxygen precipitation decreases evidently as the temperature increases above 1000 °C. In addition to the formation of new nuclei based on the VnOm complexes, the growth of grown-in oxygen precipitates is also facilitated by the incorporation of high concentration vacancies in the neutron-irradiated silicon. In nitrogen-doped silicon, the enhanced oxygen precipitation at high temperatures primarily depends on nitrogen concentration rather than vacancy concentration as a result of forming stable N2V2 complexes acting as precipitate nuclei.

Relationship between Gallium Concentration and Resistivity of Gallium-Doped Czochralski Silicon Crystals: Investigation of a Conversion Curve

The relationship between gallium (Ga) concentration and resistivity was studied in Ga-doped Czochralski (CZ) silicon (Si) single crystals in the dopant concentration range from 1×1014 to 2×1018 atoms/cm3 by the four-point probe method, inductively coupled plasma (ICP) analysis, and Hall-effect measurement. The resistivity of Ga-doped Si was found to be larger than that of B-doped Si, because Ga is not fully ionized at Ga concentrations higher than 1016 atoms/cm3 at 300 K. A conversion curve from resistivity to Ga concentration in the range from 1×1014 to 1×1017 atoms/cm3 is proposed.

Estimation of Radiation-Induced Complex Concentration in CZ-Si by IR Absorption Spectroscopy

Radiation induced complexes in low carbon concentration, low electron dose Czochralski silicon crystal are examined by infrared absorption spectroscopy. By using the highly sensitive, highly accurate measurement and arithmetic procedures, carbon-oxygen(-self interstitial)and vacancy-oxygen complexes are detected in samples with carbon concentration about 1x1016 atoms/cm3 and electron dose about 1x1016 atoms/cm2. Also, their concentrations, are estimated by evaluating the relative oscillator strength. Quantitative analysis in high quality samples will provide important information on defect behavior in irradiated crystals.

Vacancies in as-grown CZ silicon crystals observed by low-temperature ultrasonic measurements

By means of the low-temperature ultrasonic measurement, we try to observe the elastic softening due to the vacancies in as-grown silicon crystals grown by the Czochralski (CZ) method. We prepared a high-resistivity CZ silicon crystal ingot comprising the following defect-regions: the void region, the region of ring-like oxidation stacking fault, the Pv-region, the Pi-region, and the region of the dislocation clusters. Both of the elastic constants C 44 (T) and [C11(T) - C 12 (T)/2 measured for the samples taken from the Pv-region exhibit the softening of the type C Γ (T) = C Γ (0) [1 - Δ JT /(T-Θ)] which was also found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. No response of the softening to the applied magnetic field is found, as in our previous case of the non-doped FZ silicon. The observed softenings are attributed to the triply degenerate T 2 states of the vacancy accommodating two electrons with anti parallel spins. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration.

Ga segregation in Czochralski-Si crystal growth with B codoping

Codoping of gallium (Ga) and boron (B) in a Czochralski-silicon (CZ-Si) crystal has been proposed to be an effective way to improve the homogeneity of resistivity over the length of a simply Ga-doped Si crystal, by increasing the very small equilibrium segregation coefficient of Ga ( k 0=0.008). It was observed that the axial resistivity variation in a Ga- and B-codoped Si crystal was smaller than that in simply Ga-doped Si crystals. The segregation behavior of Ga and B in the codoped CZ-Si crystal growth has been investigated in the present study. The effective segregation coefficient of Ga was kept almost constant when the B concentrations were low, but it increased at higher B concentrations. On the other hand, the effective segregation coefficient of B was kept almost constant when the B concentrations were low; however, it decreased at higher B concentrations. It has been analytically demonstrated that there is strong interaction between Ga and B in a Si crystal, which leads to an increase in the segregation coefficient of Ga in Si crystal growth.

Vacancies in Growth-Rate-Varied CZ Silicon Crystal Observed by Low-Temperature Ultrasonic Measurements

The low-temperature ultrasonic experiments are performed to measure the distribution of vacancy concentration in the ingot of the Czochralski (CZ) silicon crystal grown with the pulling rate gradually lowered. The elastic softening similar to that we recently found for the floating-zone-grown silicon crystals is observed for the so-called vacancy-rich region of the ingot which contains no voids or dislocation clusters. We further uncover that the interstitial-rich region in the ingot exhibits no such elastic softening, confirming our previous conclusion that the defects responsible for the low-temperature elastic softening are the vacancies. We also disclose that the elastic softening is absent for the ring-like oxidation stacking fault (R-OSF) region of the ingot. The measured distribution of the vacancy concentration indicates that the minority point defects are perfectly cancelled by the majority point defects during the CZ crystal growth.

Defect dynamics in the presence of nitrogen in growing Czochralski silicon crystals

Many crystallographic imperfections termed microdefects form in silicon crystals during their Czochralski growth. These are the aggregates of vacancies, of self-interstitials, or of oxygen (silicon dioxide). The distribution of microdefects can be strongly influenced and controlled by the addition of impurities such as nitrogen to the crystal. A model describing the Czochralski defect dynamics in the presence of nitrogen and oxygen is proposed and solved. The reactions between vacancies and self-interstitials, nitrogen monomers and dimers, nitrogen and vacancies, and the reactions involving vacancies, oxygen, and complexes of vacancies and oxygen are incorporated, along with the formation of various microdefects. All microdefects are approximated as spherical clusters. The formation of all clusters is described by the classical nucleation theory. The clusters, once formed, grow by diffusion-limited kinetics. The microdefect distributions in Czochralski crystals growing under steady state as well as unsteady state are discussed.

Vacancies in CZ silicon crystals observed by low-temperature ultrasonic measurements

By means of the low-temperature ultrasonic measurements, we try to observe the single vacancies in the as-grown Czochralski (CZ) silicon crystal of high resistivity and commercial-base quality. The crystal ingot we adopt here is grown with the pulling rate gradually lowered to produce various regions of different point-defect states. The elastic constants C T2g( T) and C Eg( T) measured for the samples taken from the Pv-region exhibit the softening of the type C Γ ( T)= C Γ (0) [1−Δ JT/( T− Θ)] which was found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. The response of the softening to the applied magnetic field is found to be the same as in the case of the non-doped FZ silicon. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is due to the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration. For the CZ silicon crystals, the vacancies can be well observed for the Pv-region only.

Crystal-originated particles in germanium-doped Czochralski silicon crystal

Grown-in distribution and annealing behavior of crystal-originated particles (COPs) in Czochralski silicon (Cz-Si) wafer with germanium doping have been investigated. It was found that COPs with high density but small sizes were inclined to generate in germanium-doped Cz-Si (GCz-Si) wafer. The increase of boron atoms in Cz-Si crystal with the germanium doping could benefit the formation of COPs while the oxygen interstitials in GCz-Si wafer could enhance the generation of COPs with small sizes. Meanwhile, it was suggested that the germanium doping in Cz-Si would result in the poor thermal stability of COPs. It is proposed that the combination between germanium atom and vacancy could reduce the free vacancy concentration and the onset temperature for void generation, thus forming denser but smaller void. While the stress compensation induced by boron and germanium atoms could increase the vacancy fluxes in heavy-boron doped GCz-Si crystal, the presence of oxygen atom in GCz-Si would incline to benefit the formation of inner oxide walls of void, especially with small sizes. Furthermore, thinner oxide walls within void for GCz-Si crystal are considered to be charged for the easy annihilation by the germanium doping.

Limits of the copper decoration technique for delineating of the V–I boundary

Copper decoration technique was used for detection of the vacancy–interstitial (V–I) boundary in Czochralski silicon crystal. We used the technique for delineating defects in silicon previously reported by Mule’Stagno [Solid State Phenom. 82–84 (2002) 753] and we enriched it by an upgraded application of copper on the silicon surface. The new procedure is based on the deposition of elementary copper on the silicon surface from the copper nitrate solution. The new method is more efficient contrary to Mule’Stagno (2002) and it also decreases environmental drain. We compared five etchants in order to optimize the delineation of the V–I boundary. A defect region of the same diameter was detected by all the used etchants, supreme sensitivity was obtained with Wright's etchant. The outer diameter of the defect region observed by the copper decoration technique coincides with the V–I boundary diameter measured by OISF testing and approximately coincides with the V–I boundary diameter measured by COP testing. We found that the copper decoration technique delineates oxygen precipitates in silicon and we observed the dependence of V–I boundary detectability on the size of the oxygen precipitates.

First Principles Calculation of the Mechanism of Oxygen Precipitation in Czochralski Silicon Crystals (Effects of Heavy Boron Doping)

The mechanism of enhancement of the nucleation and growth of oxide precipitates (SiO2) in heavily boron (B)-doped Czochralski (CZ) silicon (Si) crystals was analyzed by first principles calculation. At the initial stage of oxygen precipitation including a small number n of interstitial oxygen (O) atoms with and without one substitutional B atom, i.e., B–On complex and On complex, reduction of the total energy of stable B–On complex formation was greater than that of stable On complex formation from isolated B and O atoms. Other calculations showed that the O atom in B-doped Si diffused as O charge state with a diffusion barrier of about 2.0 eV, which was lower than the barrier of about 2.5 eV for the O charge state in intrinsic Si. This reduction of the diffusion barrier should be the mechanism responsible for the enhanced oxygen diffusion and enhanced precipitate growth in heavily B-doped CZ Si crystals.

Defect dynamics in the presence of oxygen in growing Czochralski silicon crystals

Modern Czochralski (CZ) silicon crystals contain various crystallographic imperfections known as microdefects that affect the yield and the performance of microelectronic devices. These microdefects are primarily the aggregates of the intrinsic point defects of silicon, vacancies and self-interstitials, and of oxygen (silicon dioxide). The distribution of microdefects in a CZ crystal is determined by the complex dynamics influenced by various reactions involving the intrinsic point defects and oxygen, and their transport. Two-dimensional oxygen influenced transient defect dynamics in growing CZ crystals is quantified and solved. The Frenkel reaction and the reactions between vacancies and oxygen are considered. The formation of all microdefects is described by the classical nucleation theory. Microdefects are assumed to be spherical clusters that grow by a diffusion-limited kinetics. The predictions of the model agree well with experimental data. Various predictions of the model and experimental results are discussed.

Infrared Absorption Spectroscopy of Complexes in Low Carbon Concentration, Low Dose Irradiated CZ Silicon Crystal

Radiation induced complexes in low carbon concentration, low electron dose Czochralski silicon crystal are examined by infrared absorption spectroscopy. By using the highly sensitive, highly accurate measurement and arithmetic procedures, carbon-oxygen(-self interstitial) and vacancy- oxygen complexes are detected in samples with carbon concentration about 1x1016 atoms/cm3 and electron dose about 1x1015-16 atoms/cm2. Also, their concentrations are determined with estimated accuracy within a factor of two. It is shown that the complex concentration is proportional to the dose. Secondary defect formation is suppressed in such low carbon concentration and low dose samples. Quantitative analysis in high quality samples will provide important information on defect behavior in irradiated crystals.

The effect of carbon and antimony on grown-in microdefects in Czochralski silicon crystals

Some impurities are known to modify the properties of grown-in microdefects in Si crystals at relatively low concentrations when the only operating mechanism is trapping of either vacancies (V) or self-interstitials (I), or both, by the major impurity state. First of all, doping affects the critical value of the ratio V/ G, of the growth rate and the axial temperature gradient, that separates the range of V-based microdefects (at higher V/ G) from the range of I-based microdefects (at lower V/ G). The two representative impurities studied – carbon and antimony – exhibit opposite effects: carbon increases ( V/ G) cr thus expanding the interstitial region of a crystal, while antimony reduces ( V/ G) cr thus expanding the vacancy region. Another important effect of impurities is that microdefect formation may occur under a condition of a strong trapping which results in an reduction of the microdefect size and accordingly in an increase in the density. For carbon, a strong self-interstitial trapping (in the I-mode) is evidenced by an increased microdefect density. For antimony, vacancy trapping (in the V-mode) is apparently insignificant; void size is increased, due to an increased concentration of incorporated vacancies.

Germanium-doped Czochralski silicon: Oxygen precipitates and their annealing behavior

Czochralski silicon (Cz Si) crystals with germanium (Ge) doping are considered to be of potential application for integrated devices. In this presentation, the influence of Ge doping of Cz Si crystals on oxygen precipitate thermal stability has been discussed. Compared with the conventional Cz Si, oxygen precipitates in Ge-doped Cz (GCz) Si was proposed to be poorer stable thermally during high temperature anneals, which is ascribed to the formation of smaller precipitates. Meanwhile, the oxygen precipitation was promoted in GCz Si wafers that received a high temperature pre-anneal treatment, which has been considered to be associated with the assumption of Ge-related complexes by the intended Ge doping.

Crystal growth and oxygen precipitation behavior of 300 mm nitrogen-doped Czochralski silicon

A 300 mm, p-type, 〈1 0 0〉-oriented nitrogen-doped Czochralski (NCZ) silicon crystal was grown in a Keyex MCZ 150 crystal puller equipped with cusp magnetic field. In order to dope nitrogen into the crystal, the primary protection gas of argon was mixed with high-purity nitrogen gas at a flow rate ratio of 10:1. Due to the long time growth of crystal, any perturbation due to the SiO and cristobalite particles at the crystal/melt interface would generate dislocation in the crystal. In order to avoid this ‘disaster’ during the crystal growth, a thermal shield in connection with a protection gas director was used, thereby generating a sweeping flow over the melt to drive the SiO and cristobalite particles out of the crystal/melt interface. The oxygen precipitation behavior of a near-seed-end wafer subjected to 800 °C/8 h+1000 °C/16 h was investigated. It was found that oxygen precipitation within the P-band was stronger than that in the region outside of the P-band, which is generally not the case for the conventional Czochralski (CZ) wafer with P-band. Based on this result, it is deduced that the grown-in oxygen precipitates existing in the P-band are relatively smaller in size but with higher density compared to those in the CZ crystal.

Micro-defects in Ge doped Czochralski grown Si crystals

With the reduction in size of the features of ultra large-scale integrated (ULSI) circuits, micro-defects such as voids in Czochralski (Cz) silicon (Si) crystals play more important roles in the reliability and yield of these devices. As one of the tetravalent atoms, the behavior of germanium (Ge) doped in Cz Si crystals has attracted considerable attention in recent years. In this presentation, recent processes in the study of voids in Ge doped Cz (GCZ) Si crystals are reviewed. The grown-in characteristics of voids in GCZ wafer, including flow pattern defects (FPDs) and crystal originated particles (COPs), suggested that Ge can suppress large voids resulting in denser and smaller voids. Meanwhile, it has been found that the density of voids can be decreased by Ge doping and they can be eliminated easily in GCZ Si crystals through high temperature annealing. It is therefore speculated that the gate oxide integrity (GOI) of semiconductor devices can be improved by Ge doping. The mechanism of the effect of Ge on voids is discussed to explain the experimental results.

Defect Dynamics in the Presence of Oxygen in Growing Czochralski Silicon Crystals

Modern Czochralski (CZ) silicon crystals contain various large defects known as microdefects that affect the yield and the performance of microelectronic devices. These microdefects are primarily the agglomerates of the intrinsic point defects of silicon, vacancies and self-interstitials, and of oxygen (silicon dioxide). The distribution of microdefects in a CZ crystal is determined by the complex dynamics influenced by various reactions involving the intrinsic point defects and oxygen, and their transport. Two-dimensional oxygen influenced transient defect dynamics in growing CZ crystals is quantified and solved. The Frenkel reaction and the reactions between vacancies and oxygen are considered. The formation of all microdefects is described by the classical nucleation theory. Microdefects are assumed to be spherical clusters that grow by a diffusion-limited kinetics. The predictions of the model agree well with experimental data. Various predictions of the model and experimental results are discussed.

Defect Dynamics in the Presence of Nitrogen and Oxygen in Growing Czochralski Silicon Crystals

Many structural imperfections form in silicon crystals during their Czochralski growth. The distribution of these microdefects can be strongly influenced and controlled by the addition of impurities such as nitrogen to the crystal. A model describing the Czochralski defect dynamics in the presence of nitrogen and oxygen is proposed and solved. The reactions between vacancies and self-interstitials, nitrogen monomers and dimers, nitrogen and vacancies, and the reactions involving vacancies, oxygen, and complexes of vacancies and oxygen are incorporated, along with the formation of various microdefects-the agglomerates of vacancies, self- interstitials, and of oxygen (silicon dioxide). All microdefects are approximated as spherical clusters. The formation of all clusters is described by the classical nucleation theory. The clusters, once formed, grow by a diffusion-limited kinetics. The microdefect distributions in Czochralski crystals growing under steady state as well as unsteady state are discussed.

Defect Dynamics in the Presence of Nitrogen and Oxygen in Growing Czochralski Silicon Crystals

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