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
  • C30B29/02—Elements
  • C30B29/06—Silicon
• • 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
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/007—Pulling on a substrate
• • 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
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/20—Controlling or regulating
  • C30B15/22—Stabilisation or shape controlling of the molten zone near the pulled crystal; Controlling the section of the crystal
  • C30B15/24—Stabilisation or shape controlling of the molten zone near the pulled crystal; Controlling the section of the crystal using mechanical means, e.g. shaping guides

Definitions

• the invention relates generally to crystal growth, more specifically to ribbon crystal growth.
• Continuous silicon ribbon in this case, is formed by introducing two high temperature material strings up through a crucible that contains a shallow layer of molten silicon.
• the strings serve to stabilize the edges of the growing ribbon and the molten silicon freezes into a solid
• edges are weak and can cause cracks that propagate throughout the substrate.
• the low meniscus at the ribbon edges causes the crystal growth interface to be
• the invention features a system and method in which the meniscus height of the edges of
• crystalline ribbon grown in a continuous process can be varied and controlled. This can be done
• control of the meniscus at the ribbon edge can then be affected by the specific design and placement of the structures. In particular, the meniscus at the edge can either be made
• these structures can also have thermal properties such as thermal conductivity and emissivity that enable them to lose heat more rapidly than the surrounding melt.
• combined effect of the heat loss and modified meniscus height is to control the thickness of the edge of the growing ribbon independent of the thickness of the ribbon at its middle.
• the height of the meniscus along the width of the ribbon defines the shape of the crystal growth interface.
• the effect of changing the edge meniscus height relative to the mid-ribbon meniscus height is that the crystal growth interface shape can be controlled.
• the invention features an apparatus for growing a crystalline ribbon.
• the apparatus includes a crucible, a pair of strings, and a meniscus controller.
• the crucible holds a melt of a semiconductor material.
• the crucible has a pair of openings, through which a pair of
• the pair of strings defines the edges of the crystalline ribbon grown from the
• controller controls a property of the meniscus near the edges of the crystalline ribbon.
• the meniscus controller is a structural member located in the crucible adjacent to at least one of the strings.
• the structural member can comprise at least
• the structural member can be any suitable material.
• the structural member can be any suitable material.
• the structural member can be any suitable material.
• the pair of strings comprises a first string and a second string
• the structural member comprises a first
• the structural member placed adjacent to the first string and a second structural member placed adjacent to the second string.
• the structural member and the upper surface of the melt form a meniscus which affects the shape and height of the meniscus near the edge of the crystalline ribbon.
• the meniscus controller comprises a wall of the crucible.
• the meniscus controller provides a growth interface that is substantially flat.
• the meniscus controller provides a growth interface that is substantially convex.
• the meniscus controller controls the thickness of the crystalline ribbon.
• the meniscus controller can provide a crystalline ribbon
• the meniscus controller raises the
• the invention features an apparatus for growing a crystalline ribbon.
• the apparatus includes a crucible for holding the melt of a semiconductor material, a pair of strings passing through a pair of openings in the crucible, and a structural member disposed in
• the crucible adjacent to at least one of the strings.
• the pair of strings defines edges of the
• the structural member disposed in the crucible adjacent to at least one of the strings, raises the height of the meniscus near the edges of the crystalline ribbon.
• the invention features a method for growing a crystalline ribbon.
• a melt of a semiconductor material is provided in a crucible.
• the seed crystal is pulled from the melt between a pair of strings passing through a pair of openings in the crucible, thereby solidifying the melt to
• the crystalline ribbon and the upper surface of the melt form a
• a meniscus controller controls a property of the meniscus near the edges of the crystalline ribbon.
• a property of the meniscus is controlled using a structural member
• the structural member can be at least one pin or a generally cylindrical tube.
• a first pin or a generally cylindrical tube.
• the meniscus height at the ribbon edge can be controlled.
• the meniscus height at the ribbon edges can be controlled independently of the
• the growth interface can be made
• the thickness at the ribbon edge can be
• the thickness at the ribbon edges can be made thinner, the same, or
• the invention features a method for growing a crystalline
• a melt of a semiconductor material is provided in a crucible.
• a structural member is
• a seed crystal is pulled from the melt between the pair of strings.
• the height of the meniscus near the edges of the crystalline ribbon is raised.
• Figure 1 a shows a perspective view of a crystalline ribbon growth system.
• Figure lb shows a side view of the crystalline ribbon growth system of Figure la.
• Figure lc shows a top view of the crystalline ribbon growth system of Figure la.
• Figure 2 shows a perspective view of one embodiment of a crystalline ribbon growth system of the invention.
• Figure 3 a shows a perspective view of one embodiment of a crystalline ribbon growth
• Figure 3b shows a perspective view of one embodiment of a crystalline ribbon growth
• Figure 3 c shows a perspective view of one embodiment of a crystalline ribbon growth
• Figure 4 shows a perspective view of one embodiment of a crystalline ribbon growth
• Figure 5a shows a cross-sectional view of a ribbon crystal grown using the crystalline
• Figure 5b shows a cross-sectional view of a ribbon crystal grown using the crystalline
• Figure 6a shows a front view of a ribbon crystal grown using the crystalline ribbon growth system of Figure la.
• Figure 6b shows a front view of a ribbon crystal grown using one embodiment of the
• Figure 6c shows a front view of a ribbon crystal grown using one embodiment of the crystalline ribbon growth system of the present invention.
• Figure 7 is a schematic diagram of one embodiment of a continuous crystal growth system.
• Figure 8 is a cross-sectional view of the crystal growth system of Figure 7 cut through
• Figure 9 is a circuit diagram illustrating the resistance of the crystal growth system of
• Figure 10 shows a portion of a system for continuous ribbon crystal growth.
• Figure 1 1 shows an embodiment of a continuous ribbon crystal growth system.
• Figure 12 illustrates the calculation of the cross sectional mass area of a pile of granular
• a ribbon crystal growth system 10 includes a crucible 12, a
• crucible 12 has a pair of openings (not shown) through which the pair of strings 13 passes
• the melt 14 solidifies and forms a crystalline ribbon 15, as the ribbon is pulled from
• the pair of strings 13 stabilizes the edges of the crystalline ribbon 15.
• a meniscus 18 forms between the surface of the melt 14 and the growth interface 20 of the ribbon 15.
• the upper surface of the meniscus 18 viewed from the front is substantially concave.
• the meniscus 18 has a height h and radius of curvature Rl and R2.
• Rl represents the radius of curvature in the vertical plane
• R2 represents the
• the generalized Laplace equation can be used to determine the meniscus shape
• ⁇ p is the pressure difference between the melt surface and the height h in
• Ri and R 2 are the radii of curvature of the meniscus in the
• Ri and R 2 change with vertical height along the meniscus.
• the meniscus height and shape can be
• the meniscus height can be about 7 mm for molten silicon
• R 2 can be about half the thickness of the ribbon.
• a silicon ribbon 15 having a thickness of about 0.3 mm which has been used to grow silicon ribbon for use in solar cell applications, the meniscus height near the edge of
• the ribbon 15 can be about 0.3 mm.
• the meniscus height near the edges is significantly smaller
• Figure la illustrates the difference in height of the meniscus near the center
• a ribbon crystal growth system 30 of the present invention includes a crucible 32, a melt 34, a pair of strings 36 passing through a pair of holes in the crucible 32, and a meniscus controller 38.
• the crystalline ribbon 40 grows from the melt 34 as substantially described above with reference to Figures la-lc.
• the meniscus controller 38 modifies
• the meniscus controller 38 is a pair of structural members positioned in the crucible 32 adjacent the pair of strings 36.
• a meniscus 44 forms around each structural member 38 as the melt material wets the surface of the structural member 38.
• a liquid is said to "wet" a solid if the contact angle
• the material for the structural members 38 is selected based on the
• the material for the structural members can be graphite.
• the material for the structural members can be graphite.
• material for the structural members and/or the crucible can include carbon, oxygen, silicon,
• structural member 38 superimposes over the meniscus 42 and modifies the height of the meniscus 44 near the ribbon edges, without substantially affecting the meniscus 42 near the
• the growth interface 43 is substantially straight or substantially convex.
• these structures such as shape and size, and placement of the structures can therefore be used to control and to vary the meniscus.
• the meniscus height near the edges of the ribbon can therefore be used to control and to vary the meniscus.
• vertical pins 52 provided in the melt 54 function as the meniscus controller as shown in Figure 3a.
• two vertical graphite pins 52a, 52b are placed in blind holes in the bottom of the crucible 59 near each string 51.
• the first pin 52a is provided on one side of the ribbon 56, and the second pin 52b
• meniscus formed around each pin 52a, 52b superimposes over the meniscus 58 formed between the growth interface 60 and the melt 54, and thereby raises the height of the meniscus 58 near the edges of the ribbon 56.
• vertical walls 72 provided in the melt 74, modify the meniscus 76 near the edges of the ribbon 78 as shown in Figure 3 b.
• Each vertical wall 72 is placed near
• the crucible 71 can be separate pieces that are pinned to blind holes in the bottom of the crucible 71.
• the ribbon crystal growth system 80 includes a crucible 82
• each inner wall 84 interacts with the meniscus 86 formed between the melt 90 and the ribbon 88 and modifies the meniscus 86 near the edges of the ribbon 88.
• the meniscus 89 forms
• the ribbon crystal growth system 100 includes hollow half
• cylinders 102 face toward the ribbon edges and the outer surfaces of the cylinders 102 face away from the ribbon 104.
• An inner surface of a cylinder 102 substantially surrounds an edge of the
• the melt 106 wets the inner surfaces of the cylinders 102 and raises the height of the meniscus near the edges of the ribbon 104.
• a pair of strings 108 passes
• the hollow half cylinders 102 can be prepared by cutting full cylinders in
• full cylinders can be machined to provide an opening along the side of the cylinder, to allow the meniscus to connect from this inner surface of the cylinder to the growing crystalline ribbon.
• the structural members used as the meniscus controller can enhance cooling of the melt as the melt solidifies, and thereby provide a thicker ribbon near the edges.
• the structural members used as the meniscus controller for example, can
• the structural members usually extend above the melt and can be made of a material with an emissivity greater
• the thickness of the ribbon can be controlled. For example, meniscus
• controllers made of graphite can be used in growing crystalline silicon ribbon.
• FIGS 5a and 5b illustrate the differences in the cross sections of silicon ribbon grown
• Figure 5a shows a cross section of a ribbon 120 with
• An edge 122 refers to the region near the string 124. The result is necking near the edges 122 and weaker edges, which can lead to breakage.
• FIG. 5b illustrates significant improvement in the thickness of the ribbon 130 near the edges 132 when the meniscus is modified according to the present invention. Necking near the edges 132 is
• the meniscus controller used in the present invention also controls the shape of the growth interface.
• the growth interface can be made substantially
• Coherent twin grains have crystal structures that are mirror
• the present invention can be used with a ribbon growth system comprising a melt depth control as described in co-owned, pending U.S. Patent Application titled "Melt Depth Control for
• a continuous ribbon growth system 210 includes a crucible 212 containing a pool of molten silicon ("the melt") 214 and a pair of strings 216 extending
• the strings 216 stabilize the edges as the sheet 218 grows.
• the meniscus controller 211 modifies the meniscus.
• the surface tension of the silicon prevents leaks through
• the melt 214 and the crucible 212 are housed within an inert-gas filled housing (not shown) to prevent oxidation of the molten silicon. Rollers (not shown) keep the
• the crucible 212 remains heated to keep the
• the depth of the melt 214 is measured, and this information is provided to the feeder 226
• the feeder 226 adds silicon pellets to the melt 214 to compensate for the
• the melt 214 is measured by passing an input signal through the crucible 212 and the melt 214, and by measuring an output signal generated in response to the input signal.
• a current I ⁇ N is applied to the combination of the crucible 212 and the
• the resultant potential V OUT is measured by a differential amplifier 222 through a pair of electrodes C
• the resultant potential is fed into the feedback circuitry 224, which generates a control signal for controlling the feed rate of the feeder 226.
• feedback circuitry 224 is set up to maintain the resultant voltage at a constant level which corresponds to a desired melt height.
• the pair of electrodes C and D is positioned between the pair of electrodes A and B.
• the relationship between the melt depth and the measured output signal responsive to an input signal is described as follows.
• the present method of depth measurement utilizes unique properties of semiconductors and a commonly used crucible material (e.g., graphite). For example, at room temperature silicon is normally a semiconductor. However, at its melting
• silicon becomes a conductor of electricity almost as conductive
• Graphite is also a conductor of electricity, although conductivity of the molten silicon is greater than that of graphite and therefore dominates when measured in parallel.
• the conductivity of the silicon melt is directly proportional to the cross-sectional area of
• a change in the molten silicon melt depth changes the cross-sectional area of
• the bulk resistivity of a typical graphite material used for the construction of semiconductor processing crucibles is about one milliohm-centimeter.
• molten silicon is in the order of twenty (20) times less.
• the molten silicon can be considered to be a "shorting layer" on top of a resistive layer of
• Figure 9 illustrates a circuit diagram of the continuous ribbon growth system 210 of Figures 7 and 8.
• the present invention can further be incorporated into the crystal growth system having a
• a continuous ribbon growth system 350 includes a crucible 343 containing a pool of molten silicon (“the melt”) 342 and a pair of strings 344
• a meniscus controller 340 is positioned near each string 344.
• a thin polycrystalline sheet of silicon 341 is slowly drawn from the melt 342, as the cooler
• the meniscus controller 340 modifies the meniscus near the edges of the ribbon 341.
• melt 342 and the crucible 343 are housed within an inert-gas filled housing (not shown) to prevent oxidation of the molten
• rollers (not shown) keep the sheet 341 moving vertically as the sheet 341 grows.
• crucible 343 remains heated to keep the silicon molten in the melt 342.
• the crucible 343 also remains stationary.
• a granular source material 335 enters a hopper 312 through a large opening and exits the hopper 312 through a small opening, as shown in Figure 1 1.
• the source material 335 can have non-uniform sized particles.
• the source material for example, can be a semiconductor material.
• the source material comprises silicon and a dopant
• the source material 335 exiting the hopper 312 disposes a pile of the source material 335 on a translationally moving belt 334.
• the pile of the source material 335 has an angle of repose, which is determined by the shape and size distributions of the particles forming
• the source material 335 disposed on the moving belt 334 is
• a crucible 343 comprising a melt of the source material 335 at a predetermined rate.
• the source material is introduced into the crucible through a funnel 345 and a tube 347.
• the tube 347 is positioned inside one end of the crucible 343. In one embodiment, the
• feed rate is constant.
• the feed rate is based on the angle of repose of the source material.
• the volume of the source material is equal to the product of the mass cross-sectional area
• Figure 12 illustrates the mass cross
• the mass cross sectional area is equal to H 2 /tan ⁇ + HL, where ⁇ is the angle of
• H is the height
• L is the size of the hopper opening just above the belt.
• the belt can be controlled by the rate of movement of the belt in combination with the angle of repose.
• the belt for example, can move at a constant rate and thereby introduce the source material into
• the crucible at a constant rate.
• the belt can also move at a rate in the range from 2mm/min to lOmm/min.
• the feed rate is based on the cross sectional area of the
• the present invention which provides control of the meniscus by varying its shape and/or
• control of the ribbon thickness can be incorporated in other crystalline growth systems and methods as well.

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

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• 2000
  • 2000-06-27 JP JP2001509582A patent/JP2003504295A/ja not_active Withdrawn
  • 2000-06-27 WO PCT/US2000/017651 patent/WO2001004388A2/en not_active Application Discontinuation
  • 2000-06-27 EP EP00975147A patent/EP1198626A2/de not_active Withdrawn

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