Crystal growth apparatus and method

  • US 8,231,727 B2
  • Filed: 04/17/2008
  • Issued: 07/31/2012
  • Est. Priority Date: 04/07/2008
  • Status: Active Grant
First Claim
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1. A method for crystal growth, comprising:

  • inserting an ampoule with a crucible having a seed and raw material into a furnace having a heating source, the crucible having a crystal growth region, a seed well region with a narrower diameter than that of the crystal growth region and a tapered crystal growth region between the crystal growth region and the seed well region, the tapered crystal growth region having sidewalls tapered at an angle of 45-60 degrees;

    positioning the crucible above a crucible support cylinder that supports the crucible, the a crucible support cylinder having a funnel shape matching the tapered crystal growth region with sidewalls tapered at an angle of 45-60 degrees, such that the crucible support cylinder makes circular contact with the ampoule via only an upper rim that meets a shoulder of the tapered crystal growth region to minimize solid-to-solid contact between the crucible support cylinder and the ampoule and thereby minimize undesired/uncontrollable heating of the ampoule via conduction heating occurring therebetween, such that heat conductivity between the seed well region to an outer perimeter of the crucible support is higher than heat conductivity between an outer perimeter of the tapered crystal growth region to the crucible support, and wherein the crucible support is filled in the majority of the inside with a low density insulating material and has radiation channels penetrate from the crucible support cylinder to the seed well region, which reduces the flow of air in the crucible support and thereby minimizes undesired/uncontrollable heating of the ampoule via convection heating associated with the crucible support;

    growing a crystal using a vertical gradient freeze (VGF) process wherein the crystallizing temperature gradient within a heating source is moved relative to the crucible which is stationary to melt the raw material and reform it as a monocrystalline compound;

    controlling the heating source and the crucible support to perform monocrystalline crystal growth and to transition, at a predetermined crystal growth length of about 12-15 mm above the tapered growth region, to a crystal growth using a vertical Bridgman process on the crucible wherein the crucible is moved relative to the heating source which is stationary to continue to melt the raw material and reform it as a monocrystalline compound; and

    growing, at a predetermined crystal growth length, the crystal using a vertical Bridgman (VB) process on the ampoule in the furnace wherein the ampoule is moved relative to the heating source which is stationary to continue to melt the raw material and reform it as a monocrystalline compound;

    wherein, as a function of (1) the controlled heating of the raw material provided by the heating source and the controller during the VGF and VB processes combined with (2) the reduction of conduction heating and convection heating between the crucible support cylinder and the ampoule, accurate control of crystallizing temperature gradients are provided during VGF growth, during transition from VGF to VB, and during VB growth such that 6″

    GaAs single-crystal ingots of at least 105 mm length are reproducibly achieved having reduced body lineage defects characterized via yields of greater than 75%.

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