Technique for controlling temperature uniformity in crystal growth apparatus
A method of producing a crystalline material is provided that may include providing a crystal growth apparatus comprising a chamber, a hot zone, and a muffle. The hot zone may be disposed within the chamber and include at least one heating system, at least one heat removal system, and a crucible containing feedstock. Additionally, the method may include providing a muffle that surrounds at least two sides of the crucible to ensure uniform temperature distribution through the feedstock during crystal growth to allow the crystalline material to be grown with a square or rectangular shaped cross section.
1. A method of producing a crystalline material comprising:
providing a crystal growth apparatus comprising a chamber, and a hot zone within the chamber, the hot zone comprising a heating element having a circular cross section, a crucible having a square or rectangular cross section and containing a solid feedstock, and a heat exchanger positioned beneath the crucible;
providing a muffle having a square or rectangular cross section inside of the heating element and surrounding the crucible, wherein the muffle is thicker in each of a plurality of corners thereof than in each of a plurality of sides thereof;
covering a top of the muffle with a muffle cover disposed on an upper surface of the muffle and in contact with walls of the muffle, the muffle cover having an exit port formed therein;
fitting the exit port with a tube extending from the muffle cover to an outer surface of the chamber;
heating the solid feedstock in the crucible through the muffle with the heating element to form a liquid feedstock melt;
controlling a temperature uniformity in the crucible by orientating the muffle such that at least one corner of the plurality of corners of the muffle is positioned between a center of one side of the crucible and the heating element; and
cooling the liquid feedstock melt to produce the crystalline material.
2. The method of claim 1 , wherein the crystal growth apparatus is a directional solidification furnace.
3. The method of claim 1 , further comprising forming the solid feedstock into boule having a square or rectangular shape cross section.
4. The method of claim 1 , wherein the solid feedstock comprises alumina.
5. The method of claim 1 , wherein the crystalline material is sapphire.
6. The method of claim 1 , wherein the crystalline material is silicon.
7. The method of claim 1 , wherein the crystalline material is monocrystalline silicon.
8. The method of claim 1 , wherein the solid feedstock is heated in the crucible through the muffle with the heating element in a vacuum environment.