Czochralski Silicon Crystals Research Articles

Oxygen-induced recombination centers in as-grown Czochralski silicon crystals

Simultaneous quantitative microprofiles of the interstitial oxygen concentration and of the excess carrier lifetime were obtained, for the first time, in Czochralski-grown Si crystals employing double laser absorption scanning. It was found that oxygen concentration maxima and minima along the crystal growth direction coincide with lifetime minima and maxima, respectively. It was further found that the magnitude of oxygen-induced lifetime changes increases dramatically in going from the center to the periphery of the crystal. The present findings imply that ‘‘as-grown’’ oxygen precipitates are involved in lifetime limiting processes.

Point defect aggregates in boron doped dislocation-free Czochralski silicon crystals

Bragg line profile (BLP) and high-resolution diffuse X-ray scattering (DXS) measurements have been obtained in boron Czochralski Si single crystals. The dislocation-free crystals were doped with a B concentration ( C B) from 10 14 to 10 19cm -3 and have been analysed in a double crystal diffractometer using highly collimated Cu Kα 1 radiation. The BLP analysis proved that the (111) plane is the most affected by the doping process particularly for the higher concentrations of C B (⪆10 18 cm -3). DXS results have shown the presence of clusters with typical size parameters of some tens to some thousands of ångströms. The larger clusters have a prevailing interstitial nature and the smaller ones a vacancy nature, except for C B ∼ 10 19 cm -3 when the clusters have only an interstitial nature.

Indentation rosettes and dislocation locking by oxygen in silicon

The characteristics of indentation behavior are investigated for float-zone silicon crystals and Czochralski silicon crystals over a wide range of temperature. It is shown that the deformation process to produce an indentation is not influenced by the oxygen content. The wing length of the dislocation rosette around the indentation which is subjected to high-temperature annealing is shorter in Czochralski crystals than in float-zone crystals. The results are interpreted satisfactorily in terms of locking of dislocations by oxygen atoms in the former type of silicon crystal during their rearrangement.

Nucleation temperature of large oxide precipitates in as-grown Czochralski silicon crystal

The nucleation mechanism of large oxide precipitates in as-grown Czochralski silicon is investigated. The precipitates are square-shaped platelets with about 500 to 2600 Å half diagonal length. The nucleation temperature is determined to be around 1250 to 1000°C, utilizing measurements on the crystal cooling rate and the precipitate growth rate. The supercooling degree for the nucleation is about 50 to 300°C and is smaller than that for homogeneous nucleation. Furthermore, the observed precipitate density is considerably higher than that expected for homogeneous nucleation at these high temperatures. It is suggested that they are nucleated through a heterogeneous nucleation mechanism.

Defects in silicon crystals after the high temperature treatment

The defect formation process in dislocation free Czochralski silicon crystals after annealing at 1000 °C is studied by infrared absorption method, X-ray topography, and transmission electron microscopy. Crystals: as-grown, preliminary treated at 700 °C for 2 h or irradiated with fast pile neutrons (Φ ≈ 1019 neutrons/cm2) are used for investigations. Evidence is obtained concerning the generation and evolution of defects. Correlation between the defect concentration and the changing of interstitial oxygen content in silicon crystals is established. The oxygen precipitation process is shown to be accelerated essentially in fast pile neutrons irradiated crystals. [Russian Text Ignored]

Correlation of Oxygen and Recombination Centers on a Microscale in Asgrown Czochralski Silicon Crystals

ABSTRACTQuantitative microprofiles of the interstitial oxygen concentration and of the excess carrier lifetime, with a spacial resolution of about 20 μm, were obtained in as-grown dislocationfree CZ-Si crystals employing a double laser absorption technique. It was found that maxima (minima) in oxygen concentration along the crystal growth direction coincide with minima (maxima) of the lifetime. It was further found that the relation between changes in oxygen concentration and in lifetime varies in the radial direction indicating that “as-grown” oxygen precipitates are involved in lifetime limiting processes.

Mechanical Behavior of Czochralski-Silicon Crystals as Affected by Precipitation and Dissolution of Oxygen Atoms

The mechanical behavior of Czochralski-silicon crystals as influenced by precipitation of oxygen atoms is investigated. The magnitudes of the upper yield stress and of the stress drop after yielding are observed to decrease drastically after annealing at 1050°C and to recover on subsequent annealing at temperatures higher than 1200°C. Changes in the amount of precipitated oxygen atoms due to such annealings are followed. A theoretical analysis of the yield behavior shows that dislocations punched out from precipitates play the most important role in the softening due to precipitation.

Electrical characterization of crystal defects and oxygen in czochralski silicon using a gate-controlled diode

Defect generation in Czochralski (CZ) silicon crystal during heat treatment and effect of the defects on generation currents, measured by gate controlled diodes, were investigated. Sample wafers were obtained from an as-grown CZ silicon ingot which has a wide range of oxygen concentration but keeps other characteristics nearly constant. In the diode fabrication process, a two-step heat treatment method was utilized to control defect generation. It was found that stacking faults and dislocation loops, whose densities depend on oxygen concentration, increase the reverse current of the diode and the reverse current increases caused by defects vary with heat treatment condition. The most noticeable result was that the reverse current is enhanced by increasing oxygen concentration, even if no defect is observed in the device active region because of low defect density induced by heat treatment or of denuded zone formation. This result suggests the existence of some kind of electrically active defect caused by oxygen atoms in the crystal. Surface generation current is independent of crystal quality and two-step heat treatment conditions.

The influence of thermal point defects on the precipitation of oxygen in dislocation-free silicon crystals

The precipitation of oxygen in regularly grown and in situ-quenched dislocation-free Czochralski silicon crystals has been investigated by means of infrared absorption spectroscopy, preferential etching, and x-ray transmission topography. In addition, the effect of doping with acceptor or donor impurities on oxygen precipitation has been studied. The experimental results indicate that at oxygen supersaturation ratios smaller than 20 the formation of nuclei for precipitation predominantly occurs via a heterogeneous in which thermal point defects, in particular silicon interstitials, play an important role.

A lateral microscopic growth model for heterogeneous impurity incorporation during Czochralski crystal growth

The occurrence of heterogeneous impurity incorporation during growth of Czochralski silicon and germanium crystals is attributed to a microscopic kinetic mechanism of terrace growth. This is deduced from the close correspondence of striation patterns in bulk crystals with terrace traces in GaAs layers grown by liquid phase epitaxy. A simplified but generally applicable model of terrace growth for both epitaxial layers and bulk crystals is presented. The model does not depend on the occurence of constitutional supercooling.

Correction to "A multiple p-n junction structure obtained from As-grown Czochralski silicon crystals by heat treatment: Application to solar cells"

Correction to "A multiple p-n junction structure obtained from As-grown Czochralski silicon crystals by heat treatment: Application to solar cells"

The effect of doping on the formation of swirl defects in dislocation-free czochralski-grown silicon crystals

During the growth of macroscopically dislocation-free Czochralski silicon crystals three types of swirl defects (types A, B and C) can form. The effect of doping with electrically active impurities (B, Ga, Sb, P and As) and isoelectronic impurities (Sn) on the formation of these microdefects has been investigated by means of preferential etching, copper and lithium decoration, X-ray transmission topography and EBIC-mode SEM. Doping with donors (concentration > 10 17 cm -3) suppresses the formation of A swirl defects (dislocation loops). Doping with acceptors (concentration > 10 17 cm -3) eliminates the formation of B and C swirl defects, while doping with tin has no effect. The new experimental data strongly suggest that the formation of the different types of swirl defects is due to parallel condensation processes involving silicon interstitials and vacancies. The observed doping effects are explained in terms of complex formation as a result of coulomb attraction between dopants and charged thermal point defects.

A multiple p-n-junction structure obtained from as-grown Czochralski silicon crystals by heat treatment: Application to solar cells

Multiple p-n junctions have been prepared in as-grown Czochralski p-type silicon through overcompensation near the oxgen periodic concentration maxima by oxygen thermal donors generated during heat treatment at 450°C. Application of the multiple p-n-junction configuration to photovoltaic energy conversion has been investigated. A new solar-cell structure based on multiple p-n junctions was developed. Theoretical analysis showed that a significant increase in collection efficiency over the conventional solar cells can be achieved.

Quantitative determination of microdefect density in dislocation-free silicon by preferential chemical etching

A phenomenological equation is derived which relates the observed surface density of hillock defects in dislocation-free Czochralski silicon crystals to the bulk density, the etch rate, the etch time and a parameter which we call the defect survival time which is defined as the time interval between the defect being revealed by the etch and the feature being totally etched away. Application of a practical method, designated etching analysis with time (EAT), to the quantitative analysis of two silicon samples from the same dislocation-free crystal is described. Excellent agreement between theory and experiment is obtained.

Quantitative Analysis of Microsegregation in the Faceted and Non-Faceted Czochralski Silicon Crystal Growth

Abstract The microsegregation behaviour of antimony in the faceted and non-faceted Czochralski silicon crystal growth was analyzed quantitatively. Using small melt heights and no rotation, dopant striations of various small spacings were eliminated. Interface demarcation and spreading resistance measurements were used for the segregation analysis. The dopant concentration and its fluctuation during the faceted growth were both higher than during non-faceted growth. On the other hand, fluctuations of the microscopic growth rate were about the same in magnitude and periodicity in the two growth regions.

The effect of doping on microdefect formation in as-grown dislocation-free Czochralski silicon crystals

The influence of p- and n-type doping on microdefect formation in macroscopically dislocation-free as-grown Czochralski silicon crystals has been studied using copper decoration, x-ray transmission topography, preferential etching, and high-voltage transmission electron microscopy. B-doped crystals are found to contain undecorated perfect dislocation loops of an interstitial nature. In Sb-doped crystals two other types of microdefects are present, one of which consists of a precipitate particle exhibiting a vacancy type of strain field. All defects are distributed in a striated pattern.

Annealing behavior of the oxygen donor in silicon

The behavior of the oxygen donor in Czochralski silicon crystals was investigated by resistivity measurement. Annealing at 475 °C was employed to produce an oxygen donor, and the donor concentration was reduced to some extent by heat treatment at 550 °C for 20 h. The results were compared with those reported in the 1950’s and 1960’s. The reduction rate was far smaller than that obtained in the 1950’s, and complete annihilation was not observed, even after 20-h annealing. A model was proposed to interpret the difference in the reduction behavior of the oxygen donor between the old and today’s crystals, in terms of some species which neutralize the donor. A numerical calculation based on this model was made to predict the reduction behavior and was found to be in reasonable agreement with the experimental results.

Comparison between swirl‐type defects in float‐zone and those in czochralski silicon single crystals

AbstractComparison is presented between the morphology of „swirls”︁ etch pits occurring in the float‐zone and those in Czochralski silicon crystals after various heat treatments. It appears that the difference in the morphology of „swirls”︁ etch pits results from the difference in the structure of defects. The influence of heat‐treatment temperature and composition of the ambient atmosphere upon the density and the morphology of the etch pits have been discussed.

Formation and elimination of growth striations in dislocation-free silicon crystals

Growth striations due to inhomogeneous incorporation of dope impurities as well as residual carbon in dislocation-free floating-zone and Czochralski silicon crystals have been studied. The dope striations are detected by means of spreading resistance measurements and preferential etching, while the carbon striations are analysed using among other things a special type of X-ray transmission section topography. The relationship between various growth parameters and striation formation is determined. The influence of remelt phenomena and solid-state diffusion on striation formation is analysed and directives are obtained for the elimination of striations during crystal growth. Carbon striations are also eliminated by means of annealing treatments of the as-grown crystals.

A solution for melt-level control when growing Czochralski silicon crystals in hemispherical quartz crucibles : T. G. Digges Jr., Solid-St. Tech. February 1975. p. 44

A solution for melt-level control when growing Czochralski silicon crystals in hemispherical quartz crucibles : T. G. Digges Jr., Solid-St. Tech. February 1975. p. 44