Patent ID: 11965267
Assignee: PVA TEPLA AG
Field: Surface technology, coating (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A method for pulling a cylindrical crystal (5) from a melt (2) by a crystal pulling unit, the crystal pulling unit comprising:
a crucible (3) in which the melt (2) is disposed;
a crucible heater (4) which surrounds the crucible (3) annularly;
a crucible lifting device (7) for lifting the crucible (3);
a crystal lifting device (6) for pulling the crystal (5) from the melt (2); and
a heat shield (10) surrounding the crystal (5) annularly and having a lower edge which ends above the melt (2) and forms an annular gap (12);
and comprising the steps of:
measuring an actual value of a diameter of the crystal at a surface of the melt;
comparing the actual value with a setpoint value for the diameter of the crystal; and
setting a height of the annular gap (12) as a function of a deviation between the actual value and the setpoint value using a first controller which has a first readjustment time;
wherein when the actual value is smaller than the setpoint value the height of the annular gap (12) is reduced and wherein when the actual value is larger than the setpoint value the height of the annular gap (12) is increased;
wherein for changing the height of the annular gap (12), a lifting rate (14) of the crucible (3) and in equal measure a lifting rate (13) of the crystal (5) are varied so that a crystal pulling rate remains constant.