Apparatus and method for continuous crystal pulling

A method for continuously pulling a crystal rod, applied to an apparatus for continuous crystal pulling, the method comprising:

• providing an apparatus for continuous crystal pulling, wherein the apparatus includes:
• a crucible including a first sub-crucible and a second sub-crucible located at an inner side of the first sub-crucible, wherein a material feeding space is formed between the first sub-crucible and the second sub-crucible;
• a draft tube located above the crucible;
• and
• a delivery duct disposed corresponding to the material feeding space and configured to supply materials into the crucible;
• providing a first crystal liquid in the material feeding space formed between the first sub-crucible and the second sub-crucible, and providing a second crystal liquid in the second sub-crucible, wherein the second crystal liquid is used for forming a plurality of crystal rods, and the first crystal liquid in the material feeding space flows into the second sub-crucible to compensate for consumption of the second crystal liquid for forming the plurality of crystal rods;
• and
• providing a seed crystal for the second crystal liquid, and pulling the seed crystal from the second crystal liquid to form a crystal rod of the plurality of crystal rods,
• wherein when pulling a last one of the plurality of crystal rods, a position of the second sub-crucible and a position of the draft tube are adjusted so that a distance between an interface of the second crystal liquid in the second sub-crucible and a bottom surface of the draft tube is kept substantially unchanged,
• wherein the apparatus comprises:
• a crucible including a first sub-crucible and a second sub-crucible located at an inner side of the first sub-crucible, wherein a material feeding space is formed between the first sub-crucible and the second sub-crucible;
• a draft tube located above the crucible;
• and
• a delivery duct disposed corresponding to the material feeding space and configured to supply materials into the crucible;
• wherein a ratio of an inner diameter of the second sub-crucible to an outer diameter of the draft tube is in a range from 1.09 to 1.3, the outer diameter of the draft tube is in a range from 500 mm to 550 mm, and the inner diameter of the second sub-crucible is in a range from 600 mm to 650 mm,
• wherein the draft tube is capable of moving between a first position and a second position, in the first position, a distance between a bottom surface of the draft tube and a bottom surface of the crucible is designated as a first distance, and in the second position, a distance between the bottom surface of the draft tube and the bottom surface of the crucible is designated as a second distance while the delivery duct is adapted to extend into the material feeding space, the first distance is greater than the second distance,
• wherein in both the first position and the second position, a distance between the bottom surface of the draft tube and a crystal-liquid interface in the crucible is kept substantially unchanged, and
• wherein the draft tube comprises a straight tube portion, and a gap is formed between an inner sidewall of the second sub-crucible and an outer sidewall of the straight tube portion of the draft tube with a width in a range from 50 mm to 150 mm.