Non-contact systems and methods for determining distance between silicon melt and reflector in a crystal puller

A measurement system for use with a crystal puller having a silicon melt in a crucible and a reflector defining a central passage through which a crystal is pulled, the system comprising:

• a laser to selectively transmit a coherent light beam to a target object to produce a reflection on a surface of the silicon melt;
• a detector array to capture light through an opening in the crystal puller, the detector array directed to the surface of the silicon melt in the crystal puller;
• and
• an optical modulator to pulse the coherent light beam of the laser into discrete coherent light beams having a period;
• wherein a control system is programmed to determine measurement distances from the surface of the silicon melt by:
• controlling the laser to direct coherent light beams from the laser to the target object;
• controlling the optical modulator to pulse the coherent light beam of the laser;
• controlling the detector array to capture light;
• and
• determining a measurement distance between the surface of the silicon melt and a bottom surface of the reflector based on a location of the reflection.

A method of determining a distance between a silicon melt in a crucible and a reflector in a crystal puller using a measurement system, the method comprising:

• directing coherent light beams from a laser to a target object to produce a reflection on a surface of the silicon melt, the laser positioned outside of the crystal puller;
• pulsing the coherent light beams from the laser into discrete coherent light beams having a period using an optical modulator;
• capturing discrete light through an opening in the crystal puller using a detector array positioned outside of the crystal puller while the discrete coherent light beams are directed at the target object, the captured light including at least a part of a surface of the silicon melt on which the reflection is visible;
• and
• determining, by a control system, a distance between the surface of the silicon melt and a bottom surface of the reflector based on a location of the reflection.