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
  • C30B19/00—Liquid-phase epitaxial-layer growth
  • C30B19/06—Reaction chambers; Boats for supporting the melt; Substrate holders
• • 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
  • C30B19/00—Liquid-phase epitaxial-layer growth
  • C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
• • 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
  • C30B19/00—Liquid-phase epitaxial-layer growth
  • C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
  • C30B19/04—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux the solvent being a component of the crystal composition

Definitions

• the present invention relates to a method of producing and an apparatus for the production of liquid phase epitaxially grown crystals.
• the requirement for such materia has increased in line with growth in the electronic industry.
• Crystalline material may be produced by a number of well established techniques including Czochralski pulling, a technique in which a crystal is grown at high pressure and rotated slowly to encourage uniform growth as it is pulled from a melt, and to a lesser extent the horizontal Bridgman techniques.
• Czochralski pulling a technique in which a crystal is grown at high pressure and rotated slowly to encourage uniform growth as it is pulled from a melt
• horizontal Bridgman techniques a more pure material has been required.
• MBE Molecular beam epita
• Liquid phase epitaxy was developed to produce layers of greater thickness.
• the LPE technique is based on the tilt-tube furnace first described by Nelson (H. Nelson, RCA Review 24, 603 (1963)), and later adapted by others, particularly Hicks et al (H.G.B. Hicks and D.F. Manley, Soli State Communications, Vol.7, pp.1463-1465 (1969)), and is successful in producing epitaxial layers that are substantially thicker than those produced by MBE.
• LPE involves a liquidous-solidus reaction in which a single crystal epitaxial layer is grown on a single crystal substrate.
• the resultant epitaxial layer mimics the crystallographic arrangement of the substrate lattice.
• Two characteristics must be considered when assessing t quality of a crystal, namely the integrity of the crystallographic morphology and the level of impurities in t crystal.
• LPE utilizes substrates of high morphologic integrity as the base for the production of crystals' of enhanced purity.
• the technique may b used to produce material that has the same crystallographic structure, but differing chemical and/or physical properties to that of the substrate material. Such would be the case when LPE is used in the production of "doped" semiconductor materials, where an impurity is deliberately introduced into a crystal to change its electrical properties from that of an ideal intrinsic material to that with either an excess of conduction electrons or electron vacancies (holes) in the valence band.
• the established LPE technique utilizes an apparatus, a 0 component of which is a crucible, in which is secured the substrate upon which the epitaxial layer is to be grown.
• the crucible also contains a mixture of two components (hereinafter referred to as the melt), namely the material to be grown on the substrate (hereinafter referred to as the 5 source material) and a solvent.
• the apparatus also includes a means of heating the mixture and isolating it from the substrate until interaction is required.
• the source material Upon continued application of heat, the source material will dissolve in the solvent at a temperature which is 0 dependent upon the materials involved.
• the solvent is nearly saturated with source material, the melt is introduced to the substrate such that it covers the exposed surface of the substrate. The substrate surface partially dissolves until a solution equilibrium is established. Then upon
• the source material will begin to precipitate from the melt and epitaxial growth upon the substrate commences.
• the partial substrate dissolution (melt back) which occurs prior to the commencement of epitaxial growth is an important feature of the LPE technique as it is the solution
• the present invention provides a method of producing liquid phase epitaxially grown crystals comprising the steps of dissolving a source material into a solvent to form a melt, introducing the melt to a substrate upon which the epitaxial layer is to be grown, agitating the melt during partial substrate dissolution which results from introduction of the melt to th substrate, and further agitating the melt during deposition o an epitaxial layer on the substrate which results from allowing the melt to cool.
• melt is also agitated during dissolution of the source material into the solvent prior to the introduction of the melt to the substrate.
• the present method may be particularly useful in preparing semiconductor materials, particularly compound semiconductor materials, though it is equally applicable to the preparation of single element material such as silicon or germanium. Furthermore, the present invention is also equall applicable to the preparation of both doped and undoped semiconductor materials.
• Compound semiconductors are semiconductors made of a compound of two or more elements. Such semiconductors are commonly III-V semiconductors made from a compound of elemen from group III of the periodic table (such as aluminium, gallium, and indium) and group V of the periodic table (such as nitrogen, phosphorus, arsenic and antimony). Examples of compound III-V semiconductors include binary compounds such gallium arsenide (GaAs), ternaries such as aluminium gallium arsenide (AlGaAs), and quaternaries such as indium gallium arsenide phosphide (InGaAsP).
• GaAs gallium arsenide
• AlGaAs aluminium gallium arsenide
• InGaAsP indium gallium arsenide phosphide
• an apparatus for the preparation of liquid phase epitaxially grown crystals comprising a controlled atmosphere reaction vessel, separation means for isolating- a melt from a substrate in the reaction vessel, heating means for causing the dissolution of a source material in a solvent to form the melt, transfer means for introducing the melt to the substrate so that partial substrate dissolution occurs and during cooling deposition of epitaxially grown crystals takes place and agitation means for agitating the melt during partial substrate dissolution and the deposition of the epitaxial layer onto the substrate.
• the reaction vessel preferably includes a crucible within which heat induced dissolution of the source material within the solvent occurs.
• the crucible is preferably made from materials selected from high purity silica, graphite, boron nitride and alumina as all are resistant to breakdown at elevated temperatures and do not contribute impurities to the melt contained within the crucible.
• the substrate also is preferably located within the crucible, in which case, both the separation means for isolating the melt from the substrate and the transfer means for intr ⁇ ducing the melt to the substrate may be provided by means to mount the reaction vessel on a pivotal arrangement which facilitates movement of the reaction vessel from a first position to a second position.
• the crucible In the first position, the crucible is inclined such that the substrate is elevated relative to the melt and conversely in the second position the crucible is inclined such that the melt is initially elevated relative to the substrate and subsequently covers the substrate. Separation means and transfer means are thus facilitated when the reaction vessel is configured in the first and second position respectively.
• the substrate may be located elsewhere in the reaction vessel.
• the heating means to facilitate dissolution of the source material within the solvent is preferably provided by a furnace and the controlled atmosphere within the reaction vessel is preferably provided by a flow of Pd diffused hydrogen.
• the agitation means for agitating a melt during substrat dissolution and the deposition of the epitaxial layer onto th substrate is preferably provided by means to cause vibration of the crucible containing the melt and substrate.
• the means to cause vibration preferably comprises a rod or similar vibration conductor having a tip in contact with the crucible and connected to a transducer which in turn is connected to a power oscillator.
• the rod is composed of silica and is connected to the transducer by way of a flexible coupling which seals the silica rod into the reaction vessel (which thus remains gas tight) and minimises dampening of the vibrations induced by the transducer.
• the transducer is preferably operated with a frequency o 50 to 70 Hz and with a power input such that the crucible displacement is 0.045 to 0.055 mm.
• the agitation means may not involve physical contact between the crucible and some vibration inducing mechanism, but rather agitation may be achieved by way of electro-magnetically induced eddy currents or similar non-contact agitation means.
• Figure 1 is a schematic representation of an apparatus for the preparation of liquid phase epitaxially grown galliu arsenide (GaAs) wherein the apparatus is configured in a fir position.
• GaAs galliu arsenide
• FIG 2 is a schematic representation of the apparatus of figure 1 when configured in a second position.
• Figure 3 is an enlarged view of a portion of the apparatus illustrated in figure 2 but at time subsequent to that illustrated in figure 2.
• the GaAs crystal is grown in a silica crucible 10 contained within a controlled atmosphere silica reaction tube 11.
• the atmosphere is controlled by a flow of palladium diffused hydrogen (not illustrated) .
• Heat is supplied to the crucible 10 by way of the electric furnace 12 which partially surrounds the reaction tube 11.
• the crucible 10 is in physical contact with a silica rod 13 which is connected to a transducer 14 by way of a flexible coupling 15 which seals the silica rod 13 into the reaction tube 11 at its base 16.
• the transducer 14 is operated with a frequency of 60Hz, drawing a power input from the power oscillator 17 such that a crucible displacement of 0.05mm results.
• the crucible 10 contains a melt 18 consisting of GaAs source material and a gallium solvent together with a GaAs substrate 19 of the ⁇ 100> orientation which is anchored in the crucible 10 by way of a silica clamp 20.
• the reaction tube portion of the apparatus is mounted on a pivoting arrangement 21 which facilitates movement of the reaction tube 11 from a first position as illustrated in figure 1 to a second position as illustrated in figure 2.
• the apparatus Prior to the growth of a GaAs crystal, the apparatus is arranged with the reaction tube 11 in the first position (figure 1) and the crucible 10 is loaded with both the melt 18 and the substrate 19. Heat is applied to the crucible 10 fro the furnace 12 and vibration of the crucible 10 is commenced by applying power to the transducer 14. As the temperature rises, GaAs particles begin to dissolve in the gallium solven and the resultant melt's homogeneity is maintained by the "stirring" effect of the vibrations transmitted to the crucible. When the temperature of the melt has reached approximately 830°C at which time the gallium solvent will be practically saturated with GaAs, the reaction tube 11 is transferred to the second position (figure 2) by movement of the pivoting arrangement 21.
• the source of heat is then reduced to provide a controlled rate of temperature decrease.
• the melt 18 is thus introduced to the substrate 19 such 19 (figure 3) with resulting partial dissolution (melt back) of the substrate surface until a solution equilibrium is established, followed by growth of the GaAs from the gallium onto the substrate surface.
• Vibration of the crucible 10 is continued throughout this process with the result that the problems of imperfect initial dissolution of the substrate a gallium inclusions in the growing epitaxial layer due to a combination of thermal convection currents and constitutional supercooling are mitigated with resulting production of GaAs crystals of enhanced quality.
• vibration of the crucible 10 is discontinued and the reactio tube 11 is returned to the first position as illustrated in figure 1 by movement of the pivoting arrangement 21.
• the remaining melt 18 is decanted from the surface of the freshl grown GaAs crystal.
• the resultant crystal may subsequently removed and further processed as desired.
• the remaining mel can be successfully reused in the growth of further crystals and additional GaAs may be periodically added to the melt to replenish that consumed in epitaxial growth.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)

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• 1990
  • 1990-04-24 WO PCT/AU1990/000163 patent/WO1990012905A1/fr not_active Application Discontinuation
  • 1990-04-24 EP EP19900906735 patent/EP0470130A4/en not_active Withdrawn

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