WO2014202284A1 - Dispositif et procédé de cristallisation pour la cristallisation à partir de masses fondues électriquement conductrices ainsi que lingots pouvant être obtenus par le procédé - Google Patents

Dispositif et procédé de cristallisation pour la cristallisation à partir de masses fondues électriquement conductrices ainsi que lingots pouvant être obtenus par le procédé Download PDF

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Publication number
WO2014202284A1
WO2014202284A1 PCT/EP2014/059684 EP2014059684W WO2014202284A1 WO 2014202284 A1 WO2014202284 A1 WO 2014202284A1 EP 2014059684 W EP2014059684 W EP 2014059684W WO 2014202284 A1 WO2014202284 A1 WO 2014202284A1
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WIPO (PCT)
Prior art keywords
heater
crucible
ingot
magnet module
crystallization
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PCT/EP2014/059684
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German (de)
English (en)
Inventor
Natascha Dropka
Christiane Frank-Rotsch
Ralph-Peter Lange
Petra Krause
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Forschungsverbund Berlin E.V.
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Publication of WO2014202284A1 publication Critical patent/WO2014202284A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/42—Gallium arsenide
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/007—Mechanisms for moving either the charge or the heater
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B30/00—Production of single crystals or homogeneous polycrystalline material with defined structure characterised by the action of electric or magnetic fields, wave energy or other specific physical conditions
    • C30B30/04—Production of single crystals or homogeneous polycrystalline material with defined structure characterised by the action of electric or magnetic fields, wave energy or other specific physical conditions using magnetic fields
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure

Definitions

  • the invention relates to a crystallization plant for the production of ingots by directional solidification of electrically conductive melts, a process for growing crystals by means of the aforementioned crystallization plant, as well as ingots produced or preparable by the process with homogeneous properties.
  • a heater-magnet module arrangement (HMM) is disclosed specifically for the crystallization of PV silicon in rectangular containers, which incorporates a rectangular, concentric ceiling heater for the generation of Lorentz force densities.
  • a combination of lateral heater magnet module and ceiling heater is shown.
  • the expected Lorentz force density in this arrangement is directed in an analogous manner to a laterally arranged heater-magnet module inwardly to the imaginary center.
  • the electrical leads of the ceiling heater which are routed directly horizontally across the coil windings, would completely extinguish a magnetic traveling field generated in this area, so that the ceiling heater is unsuitable for targeted generation of Lorentz force density distributions in electrically conductive melts.
  • DE 10 2010 041 061 A1 discloses a method and an apparatus for producing crystals by directional solidification from electrically conductive melts.
  • the device has a crucible for holding the melt, a ceiling heater and a Power supply unit.
  • a magnetic field can be set, which generates a crystallization front with a convex contour
  • Ingots can be monocrystalline or polycrystalline.
  • Monocrystalline ingots can be produced by different crystal growing methods. As a rule, the growth takes place from the melt, wherein the Czochralski method is usually used in silicon and other semiconductor materials.
  • Polycrystalline ingots (also referred to as multicrystalline ingots) are mainly used as Si ingots in photovoltaics for the production of solar cells and in micromechanics. If in the course of the application case by case of crystal or single crystal is mentioned, so hereby a monocrystalline ingot is meant.
  • the object of the invention is to provide a method and suitable arrangements in order to further increase the crystal quality, in particular the homogeneity.
  • the crystallization plant includes:
  • each crucible is associated with a heater-magnet module
  • a control and power supply unit for the heater-magnet module iiii. a control and power supply unit for the heater-magnet module.
  • the heater-magnet module (HMM) assigned to the respective crucible is arranged and electrically driven in such a way that a Lorentz force density field can be generated, which is directed in such a way that the resulting force acts outward in the direction of growth relative to a geometric center axis of the crucible ,
  • the crystallization plant according to the invention accordingly has one or more crucibles.
  • Each crucible is assigned a heater-magnet module.
  • the heater-magnet module is arranged above in such a way that it is aligned centrally or substantially centrally to the geometric center axis of the crucible (hereinafter also referred to as ceiling heater-magnet module (DHHM)).
  • DHHM ceiling heater-magnet module
  • the heater-magnet modules are driven in a conventional manner by specifying amplitude, phase angle, etc. for generating a traveling magnetic field in the melt. In this case, the magnetic field in the melt is influenced so that a directed from the inside to the outside and thereby in the direction of the crystallization front flow is generated in the melt.
  • the resulting force action of the Lorentz field thus extends at an angle to the geometric center axis of the crucible.
  • the invention thus provides a novel apparatus for directional crystallization of preferably semiconductor crystals of electrically conductive melts in crucible arrangements according to the vertical gradient method (VGF) as the preferred method.
  • VVF vertical gradient method
  • the invention enables the generation of Lorentz forces directed downwardly and radially outwardly from any imaginary point of the melt, and thereby simultaneously mixing the melt and producing a convexly curved solid-liquid phase boundary without inflection points.
  • the Lorentz forces are by means of one above the crucible arranged heater magnet module (ceiling heater magnet module (DHMM)) produced analogously to the so-called KristMAG method.
  • the coils of the ceiling heater magnet module are preferably fed with alternating current at a phase angle, wherein the phase angle between the coils may increase from the center, but is variable.
  • Convex phase boundaries are also adjustable using this arrangement, but there is always an undesirable concave portion of the phase boundary shape near the crucible edge. This concave portion can trigger polycrystalline structures in single crystal growth.
  • the new arrangement can also be applied to Bridgman or DS crystallization plants, in which case the outer edge of the ceiling heater module preferably follows the outer crucible edge shape. Also in the crystallization of multicrystalline material, such. As PV silicon, the avoidance of W-shaped solid / liquid phase boundary is positive for the yield of higher quality material, since the beginning of the crucible edge ingrowth of very small grains can then be reduced.
  • the power supply lines to the heater magnet module form an angle which ensures that the magnetic field induced by the power supply lines suppresses the magnetic field of the heater magnet. Module not affected.
  • the electrical leads are arranged parallel to the central axis of the crucible. In the described novel crystallization system so the power supply lines are arranged so that they are close to the Schuerwindung (coils) perpendicular and are performed radially only at the maximum distance.
  • a preferred embodiment of the invention provides that the outer shape of the heater-magnet module according to the invention is concentric. As a result, it is preferable, but not essential, for the inner crucible shape to follow a circle as well.
  • the resulting advantage is that the resulting Lorentz force field and, as a result, the flow field in the melt can be set highly symmetrical with a less expensive and thus less error-prone control and has a minimum density of perturbations.
  • one or more coils of a heater-magnet module preferably form a circle or a spiral.
  • the heater magnet module, in particular the ceiling heater magnet module consists of any number of coils. Here, various types of arrangement are possible.
  • the coils of the heater-magnet module thus form a spiral whose spiral winding is divided into two or more coils electrically isolated from each other (preferably 2 to 4 coils).
  • the spiral may take the form of an Archimedes spiral (equivalent pitch), logarithmic spiral or spring-form spiral.
  • Circular embodiments of the heater-magnet module can be obtained, for example, by two or more coils arranged annularly around the center point of the heater-magnet module.
  • the annular coils may in each case comprise a plurality of turns running around the middle point, wherein a transition between the individual turns of a coil preferably takes place stepwise in order to obtain largely concentrically constructed coil turns.
  • the heater-magnet modules are to use coils of different winding height or with a different winding cross-section. Furthermore, the coils can be arranged at different distances from the crystallization front; the coils are then not arranged in a common plane of the heater-magnet module. Alternatively or additionally, a variation of the winding height, the winding cross-section or distance to the crystallization front is also conceivable within a single coil. The variation of the Lorentz forces and the heat distribution with a heater-magnet module, which includes only a single coil, is particularly preferred because the power supply is much easier.
  • the crystallization plant preferably has two or more crucibles (More crucible assembly). Each crucible is associated with a heater-magnet module of the embodiment described above. The number of crucibles can be chosen arbitrarily. The heater-magnet modules induce an equal or largely equal Lorentz force field in each crucible. Thus, it is possible to grow crystals of very high similarity and quality simultaneously.
  • a further aspect of the invention is the provision of a method for crystal growth from electrically conductive melts, which comprises the following (successive) steps:
  • the method according to the invention enables the preparation of crystals with high homogeneity with respect to crystal quality, in particular a homogeneous, low dislocation density in single crystals.
  • a Lorentz force field is preferably induced, which is centrosymetric metric, in which therefore the resulting Lorentz forces act zentrosym metric.
  • the ceiling heater magnet modules of the crystallization system can be operated by means of predetermined current amplitudes. It is also conceivable to modulate the applied alternating current for the generation of the Lorentz force densities in the melt, for example in the form of a sinusoidal modulation.
  • the modulation can be a variation of the amplitudes of the AC, the amplitudes of the modulation itself, as well as the periods of modulation include.
  • the temporal modulation of the current can be done with different parameters. Due to the modulation particularly symmetrical temperature and magnetic field distributions can be generated in the crucible used, because slightly existing asymmetries in the generated magnetic field are averaged.
  • the geometry and relative position of the individual coils in the heater-magnet module is observed.
  • the coils are driven sequentially in such a way that they generate a time-dependent magnetic traveling field in the melt.
  • the frequency significantly affects the penetration depth and strength of the Lorentz forces thereby affecting the direction of the Lorentz forces.
  • the penetration depth decreases and the intensity of the Lorentz forces and the inclination angle of the Lorentz force to the winding surface increase.
  • the choice of frequency still depends on the electrical conductivity of the melt and thus also on the desired penetration depth.
  • the phase shift affects the Lorentz force intensity only relatively weak (weak at low frequencies, but the influence of the phase shift increases at higher frequencies).
  • the influence of the phase shift on the direction of the Lorentz forces is significant. As the phase shift increases, the intensity decreases, with the optimum depending on the frequency. In general, the phase shift should be set such that the resulting Lorentz force is at a slope away from the central vertical axis of the melt. By appropriate specifications of the phase shift or alignment of the Lorentz force, the direction of the magnetic traveling fields generated can be influenced. The current amplitude directly determines the Lorentz force intensity; with increasing amplitude, the Lorentz force increases sharply. The Lorentz force should be higher than the buoyancy force in the melt.
  • the method according to the invention can be used both for semiconductor materials (arsenides, silicon, germanium, etc.) and other electrically conductive materials such as molten metal or oxides.
  • the process described leads to monocrystalline ingots which differ in their crystal properties from conventionally prepared ingots. These ingots provide one another aspect of the invention.
  • Monocrystalline ingots which can be prepared or prepared according to the invention can be distinguished from known monocrystalline ingots as described below. This is defined
  • a core portion constructed of a body having the same central axis as the outer shape of the ingot and whose base G K corresponds to seven tenths of the root area Gi of the ingot;
  • edge region constructed from the according to i. remaining hollow body whose base G R corresponds to three tenths of the base G K of the ingot.
  • the edge area is thus defined so that it is perpendicular to each cut surface perpendicular to
  • Central axis of the ingot corresponds to one third of the total area of the cut surface and always has the greatest possible distance from the central axis.
  • the ingots according to the invention can now be characterized, inter alia, by a mean etch pit density EPD (R) in the edge region exceeding a mean etch pit density EPD (K) in the core region by a maximum of 75%. It therefore applies:
  • the orientation according to the invention of the Lorentz forces in the direction of the crucible edge avoids the occurrence of a point of inflection in the crystallization front near the edge of the crystal.
  • ingots produced by the process have significantly altered crystal properties, which can be characterized, for example, by a deviating radial profile of the dislocation density p.
  • the dislocation density p is the total length of all dislocation lines per unit volume in a crystalline solid.
  • One known way of visualizing dislocations and determining their density is to etch the crystals in question on a surface. This results in so-called etching pits whose density can be counted in a light microscope (eg according to DIN specifications). The resulting etch pit density, engl.
  • Etching pit density, EPD for short is a measure of the quality of semiconductor wafers, especially in the semiconductor industry.
  • the EPD is determined radially, ie along a line from the center of the crystal center to the edge of the crystal. This line runs along a half-shell on a cutting plane transverse to the growth direction of the crystal.
  • the radial EPD curve in ingots according to the invention is not W-shaped, that is, the course does not decrease from the middle to the edge, then again increase sharply in the outer edge region. Rather, a nearly constant radial EPD results.
  • the EPD is 120% higher in the edge region than at the lowest point in the core region and increased by 85% over the mean in the core region.
  • the increase in the dislocation density in the edge region of the crystals is particularly pronounced in the ⁇ 100> direction (investigations on a VGF GaAs crystal with a diameter of 100 mm).
  • the average EPD is at most 75% above the mean value of the EPD of the core region, in particular at most 50% above the mean value of the core region, ie EPD (R) ⁇ li EPD (K), more preferably at most 25% above the EPD in the core region.
  • the intrinsic defect density is measured in certain areas. Defective concentration refers to the ratio of the number of defects in the lattice structure of a solid to the total number of lattice sites. Lattice defects in a solid occur because they bring an entropy gain through disorder.
  • the homogeneity of the intrinsic defect density over the crystal can now be used.
  • the intrinsic defect density (EL2) is determined in the edge region and core region, the edge region and core region being specified again, as previously in the determination of the etching pit density.
  • the self-defect density is usually considerably lower in the edge region than in the core region.
  • the self-defect density EL2 (R) in the edge region is at most ⁇ 50%, preferably ⁇ 25%, in particular ⁇ 10% lower than the self-defect density EL2 (K) in the core region.
  • the electrical resistance distribution (EU) can also be determined radially and used to delineate the ingots according to the invention from conventionally produced ingots.
  • the electrical resistance distribution EU (R) in the edge region is increased by at most ⁇ 10%, preferably ⁇ 5%, in comparison with a resistance distribution EU (K) in the core region.
  • Edge and core area are as defined above.
  • an improved mixing of the melt is achieved, which, for example in the case of GaAs crystals, has an effect on the distribution of As precipitates in the crystal and thus on the particle number on the polished surface of a cut in the radial direction of the ingot. Particularly large As precipitates appear on the polished surface as particles (diameter> 0.3 ⁇ ). By reducing the As precipitates and distribution of the As excess in GaAs in uniformly distributed precipitates in sizes ⁇ 0.3 ⁇ therefore smaller numbers of particles could be achieved.
  • the ingots according to the invention in particular monocrystalline ingots, can also be distinguished from conventionally produced ingots in that the particle number PZ (R) in the edge region shows a smaller deviation from the particle number PZ (K) in the core region.
  • the particle number PZ (R) in the edge region is at most ⁇ 10%, preferably ⁇ 5% higher than the particle density PZ (K) in the core region. Is inevitable also the cumulative particle number PZ is lowered over the edge and core region in the ingot produced according to the invention.
  • particle numbers PZ ⁇ 40 per wafer (100 mm diameter) and for a crystal with 150 mm diameter ⁇ 75 cm "2 result .
  • ingots which can be produced or produced according to the invention in particular monocrystalline ingots, can thus be distinguished by one, several or all of the following properties from known ingots:
  • a ratio of etch pit density EPD (K) in the core region to etch pit density EPD (R) in the edge region satisfies the formula: EPD (R) ⁇ EPD (K); b) a stress distribution SV (R) in the edge region is not increased by more than 100% in comparison to a stress distribution SV (K) in the core region;
  • an electrical resistance distribution EU (R) in the edge area is increased by at most ⁇ 10% compared to a resistance distribution EU (K) in the core area; and d) a particle number PZ (R) in the edge region is increased by at most ⁇ 10% in comparison to a particle density PZ (K) in the core region,
  • the core region is constructed from a body having the same central axis and corresponding to the outer shape of the ingot, the base area of which corresponds to seven tenths of the base area of the ingot.
  • the edge area is constructed from the remaining hollow body, the base area of which corresponds to three tenths of the base area of the ingot.
  • the base of the ingot corresponds to the area which results in a section perpendicular to the central axis of the ingot.
  • the crystallization process according to the invention can be used in particular for the production of ingots from materials having electrical conductivities in the range from 10 to 10 8 S / m.
  • the method according to the invention is preferably suitable for the growth of single crystals, such as GaAs with larger diameters (100-200 mm).
  • the GaAs single crystal has in particular one or more of the properties mentioned under a) to d).
  • FIG. 1 is a schematic sectional view through a crystallization system with laterally arranged a crucible heater magnet modules according to the prior
  • 2A-D are schematic sectional views through a crystallization system with above a crucible arranged heater magnet modules in four embodiments,
  • Fig. 3A-C are schematic representations of arranged in heater-magnet modules
  • 4A-C are schematic representations of winding shapes in coils of a device according to the invention.
  • FIG. 5 shows a ceiling heater magnet module in the form of an Archimedes spiral with two
  • 6A / B show a simulated Lorentz force density distribution in a GaAs melt generated by a ceiling heater magnet module consisting of 3 coils, generated with differing AC frequency
  • FIGS. 7A-E show time-sinusoidal modulations of the Lorentz force in the melt
  • FIGS. 8A / B simulated three-dimensional temperature distributions of a crystal after one
  • Embodiment of the method according to the invention in the case of a) sinusoidally modulated current intensity and b) constant alternating current amplitude in the control of a heater-magnet module according to the invention,
  • Fig. 10 is a schematic representation of a constructible core
  • FIG. 1 1 is a schematic representation of a ceiling heater magnet module according to a further embodiment of the invention, each with a coil as a multi-pot arrangement of four crucibles.
  • FIG. 1 shows in a highly schematic manner a sectional view through a crystallization unit 1 according to the prior art.
  • the crystallization unit 1 comprises a crucible 10 for receiving an electrically conductive melt 30.
  • standard heaters 60 and 62 respectively, are arranged in the lid or base of the crystallization unit 10.
  • heater-magnet modules 20 Laterally arranged on the crystallization unit 1 are heater-magnet modules 20, which comprise three coils 21 in the illustrated embodiment.
  • the heater-magnet module 20 can be controlled by means not shown power supply lines such that a directional Lorentz force field 40 results.
  • the resulting Lorentz force field 40 points to a geometric center axis 50 of a growing single crystal 32, wherein the geometric center axis 50 of the crystal coincides with the geometric center axis 50 of the crucible.
  • the force field of the displacement direction of a solid / liquid phase boundary 31 is directed opposite.
  • a directed Lorentz density force field 40 acts as a function of its parameters (for example, strength, direction, distribution, etc.) on the particle movement of an electrically conductive melt 30, so that by controlling the parameters of the Lorentz force field 40, a thorough mixing of the melt 30, and the shape of the solid / liquid-phase boundary 31 can be induced and controlled.
  • Convex phase boundaries 33 can also be set using this application, but there is always an undesirable concave portion of the phase boundary 34 in the vicinity of the crucible edge. This concave portion of the phase boundary 34 can trigger polycrystalline structures.
  • FIGS. 2A-C show crystallization plants 1 in four embodiments.
  • the crystallization unit 1 allows the directed crystallization of single crystals of electric melts in crucible arrangements according to the vertical gradient method (VGF), but is also applicable to crystallization systems according to the Bridgman or DS method, wherein the outer edge of the lid preferably follows the outer crucible shape.
  • VCF vertical gradient method
  • a heater-magnet module 20 is arranged above the crucible.
  • the heater magnet module 20 comprises two coils each.
  • the solid / liquid phase boundary 31 can be influenced by generating a Lorentz force field.
  • alternating current is fed with a phase angle into the coils of the heater-magnet module 20, wherein the phase angle between the coils increases from the center to the outside.
  • Alignment of the Lorentz forces in the direction shown to the edge of the crucible has not previously been described and enables novel possibilities of influencing the shape of the solid / liquid phase boundary 31 (crystallization front) during crystallization.
  • the resulting Lorentz force field 40 is directed outwardly as shown in FIGS. 2A-C and thus induces a convexly curved solid-liquid phase boundary 31. Unlike the arrangement in the prior art in FIG. 1, this also applies to the edge region.
  • Degrees of freedom in the alignment of the resulting Lorentz field are adjustable by the arrangement of the turns of the individual coils 21 and the coils to each other.
  • the two windings for example, of an Archimedes spiral are arranged at the same height.
  • the Lorentz force field 40 is controlled by the parameters of the supplied alternating current, such as current and amplitude.
  • Another embodiment of the crystallization plant according to the invention are spirals 21 with variable winding height (see FIGS. 2C / D); Here, by varying the winding height, the distribution of the Lorentz force density 40 and the heat distribution in the melt 32 can be adjusted in a targeted manner.
  • the winding height allows the variation of the Lorentz forces 40 and the heat distribution even in arrangements with only one coil 21. In the described arrangements, embodiments are also possible in which the turns of the coil 21 are not in one plane.
  • the freely selectable distance of the individual windings to the crystallization front opens up further freedom in the adjustment of the temperature and magnetic fields in the melt (see FIG. 2A).
  • FIGS 3A-C show a selection of possible embodiments of the coils 21 in concentrically shaped heater-magnet modules.
  • 3A a so-called star-shaped coil 21 is shown (the heater-magnet module here comprises only a single coil), while FIG. 3C shows a typical Archimedes spiral composed of three coils 21.1.
  • the spiral arrangement of two coils shown in FIG. 3B 21.1 and 21.2 has stepped windings.
  • the coils arranged in the heater-magnet module 20 according to the invention can also vary in the arrangement of the turns.
  • the coils arranged in the heater-magnet module 20 according to the invention can also vary in the arrangement of the turns.
  • the coils arranged in the heater-magnet module 20 according to the invention can also vary in the arrangement of the turns.
  • FIG. 4B logarithmic forms
  • FIG. 4C spring-forming spirals
  • FIG. 5 shows an exemplary embodiment of a heater-magnet module 20 according to the invention, which is arranged as a ceiling heater above the crucible 10.
  • the heater-magnet module 20 is composed of an inner coil 21.1 and an outer coil 21.2, which are designed concentrically in the form of an Archimedes spiral. Also shown are the power supply lines 221 and 222 of the inner coil 21.1, as well as the power supply lines 231 and 232 for the outer coil 21.2, designed as a connection for AC voltage.
  • it is important to perform the power supply lines so that they are perpendicular to the windings of the heater magnet module and parallel only at the greatest possible distance. Otherwise, the Lorentz force field generated by the heater-magnet module 20 could be completely or partially extinguished, which in turn would lead to inhomogeneities in the melt and ultimately to polycrystalline inclusions.
  • a crystallization plant 1 with a multi-seal arrangement is shown in FIG. 11.
  • the crystallization unit 1 comprises a total of four crystallization units of the same structure.
  • a unit comprises in each case a crucible 10 and a heater magnet module 20 with a coil 21 arranged above the crucible opening.
  • Each coil 21 has two power supply lines 211, 212 with a connection for alternating current at the inner starting point of the coil 21 and a further connection on the coil outer end point of the coil 21st
  • the power supply lines 21 1, 212 of the individual coils run first perpendicular to the turns of the coils 21 upwards and then in a star shape to a central terminal 200, which in turn is arranged concentrically above the crucible arrangement. Above the central terminal 200, the terminal 201 for the coil starts and the terminal 202 for the coil ends again apart to be connected to a power source, not shown.
  • FIGS. 6A / B show simulations of a Lorentz force density distribution in a GaAs melt produced by a heater magnet module according to the invention consisting of 3 coils.
  • the distribution of the Lorentz force field is controllable by parameters of the applied alternating current, such as the frequency, as well as the phase angle between the coils.
  • a device can be operated both by the supply of predetermined current amplitudes, as well as driven by an additional novel method.
  • the alternating current which is used for generating the Lorentz force densities in the melt is preferably time-modulated sinusoidally. It is possible to change the amplitudes of the alternating current, the amplitudes of the modulation, as well as the period of the modulation.
  • the temporal modulation of the current can be done with different parameters, as shown in Figures 7A-E. In one embodiment, modulation with a period of 20 seconds ( Figure 7D) proved to be particularly suitable.
  • the mentioned variants of the method can produce particularly symmetrical temperature and magnetic field distributions in the crucibles used and contain slightly existing asymmetries in the generated magnetic field.
  • FIGS. 8A / B three-dimensionally show the temperature distributions in a crucible.
  • the distance between the lines is a measure of the temperature profile, the temperature increases with increasing line spacing.
  • the temperature shows in a range of 1550 K to 1600 K particularly closely spaced lines.
  • the partial representations illustrate the influence of sinusoidally modulated current intensity (FIG. 8A) and the influence of a constant alternating current amplitude (FIG. 8B) on the temperature field.
  • An ingot produced according to the invention is characterized in that it is homogeneously crystalline over its entire radial extent, ie from its core region to the edge region, in comparison to ingots which are cultivated according to the prior art.
  • a measure of this radial homogeneity is, for example, the dislocation density.
  • the dislocation density over etch pit density (EPD) is experimentally accessible. This is determined by treating the crystal surface to be considered with a selectively etching reagent. This creates trenches at the dislocations, which are visible under a microscope as lines whose number per unit area corresponds to the ⁇ tzgrubenêt.
  • FIG. 9 shows the course, determined experimentally for the surface, of the etched pit density of a half-shell of a GaAs produced by the known KristMAG process, which surface is determined experimentally.
  • Crystal solid line
  • the abscissa shows the distance a from the central axis of the crystal.
  • the central axis falls in the coordinate origin.
  • the ordinate carries the experimental EPD of the two crystals.
  • the typical W-shape (seen in the figure only as a "half W” since only a half-shell is shown), which is the dislocation density of a prior art crystal.
  • the maximum value of the etched pit density of the investigated crystal is almost double in the edge region For crystals produced by the process according to the invention, it is to be expected that they do not show this typical W-curve of the etch pit density. As FIG. 9 shows, the etch pit density increases moderately from the core region to the edge region. but does not go through a local minimum.
  • edge region 56 and core region 55 of a crystal 32 is shown schematically in FIG.
  • the core region 55 is to be understood as a body whose outer shape corresponds to the crystal form.
  • the base 51 of the body in the core region 55 is reduced by a third at the same height.
  • Cutting the core region 55 out of the crystal 32 results in a hollow body forming the edge region 56.
  • the base area 51 of the hollow body and thus of the edge area 56 corresponds to one third of the base area of the crystal 32.
  • the base area of the crystal 32 thus results from the sum of the base areas 51 of the core area 55 and the base area 52 of the edge area 56.
  • the central axes 50 of all three bodies , So the core portion 55, edge portion 56 and crystal 32 coincide.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)

Abstract

L'invention concerne un dispositif de cristallisation pour la production de cristaux par une solidification orientée à partir de masses fondues électriquement conductrices comprenant : - i. au moins un creuset (10) pour recevoir la masse fondue; - ii. un module dispositif chauffant-aimant (20) présentant une ou plusieurs bobines (21) et les lignes d'alimentation électrique correspondantes (200), un module dispositif chauffant-aimant étant associé à chaque creuset; et - iii. une unité de commande et d'alimentation électrique pour le module dispositif chauffant-aimant (20). Le module dispositif chauffant-aimant (20), associé au creuset respectif, est disposé et commandé électriquement de manière telle qu'un champ de densité de force de Lorentz (40) peut être généré, qui est orienté de manière telle que l'action de la force résultante, par rapport à un axe central géométrique (50) du creuset (10), agit vers l'extérieur contre le sens de croissance. Un autre aspect de l'invention concerne un procédé qui utilise le dispositif de cristallisation selon l'invention ainsi qu'un lingot qui peut être produit au moyen du procédé et/ou du dispositif de cristallisation.
PCT/EP2014/059684 2013-06-21 2014-05-13 Dispositif et procédé de cristallisation pour la cristallisation à partir de masses fondues électriquement conductrices ainsi que lingots pouvant être obtenus par le procédé WO2014202284A1 (fr)

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