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

A measurement system comprising:

• a target object at least partially visible through an opening in a crystal puller, the crystal puller having a silicon melt in a crucible and a reflector defining a central passage through which a crystal is pulled;
• a detector array to capture light through the opening, the detector array directed to a surface of the silicon melt in the crystal puller and to the target object;
• a laser to selectively transmit a coherent light beam through the same opening through which the detector array captures light, to the target object to produce a reflection of the target object on the surface of the silicon melt;
• an optical modulator to pulse the coherent light beams of the laser into discrete coherent light beams having a period;
• and,
• a lock-in amplifier connected to the detector array to filter discrete coherent light having the period from captured light;
• wherein a controller is programmed to determine measurement distances from a surface of the silicon melt while the crystal is being pulled from the silicon melt by:
• controlling the laser to direct coherent light beams from the laser to a first end of the target object, the first end visible by the laser through the opening;
• controlling the optical modulator to pulse the coherent light beam of the laser;
• controlling the detector array to capture light;
• controlling a lock-in amplifier to filter discrete coherent light beams having the period from the captured light, the lock-in amplifier connected to the detector array;
• and,
• determining, by the controller, a measurement distance between the surface of the silicon melt and a bottom surface of the reflector based on a location of the reflection of the target object.

A method of determining a distance between a silicon melt in a crucible and a reflector in a crystal puller while a crystal is being pulled from the silicon melt using a measurement system:

• directing coherent light beams from a laser to a target object mounted on the reflector and visible through an opening, 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, wherein the optical modulator is selected from a pulse width modulator and an optical chopper, wherein the pulse width modulator is connected to the laser and pulses the coherent light beams of the laser, wherein the optical chopper is positioned between the laser and the target object to chop the coherent light beams of the laser;
• capturing discrete light through the same opening through which the coherent light beams are directed 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 of the target object is visible;
• and
• determining, by a controller, a distance between the surface of the silicon melt and a bottom surface of the reflector based on a location of the reflection of the target object.