Crystal Puller Melt-Reflector Distance Sensing Under Thermal Light
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Solution Overview
Problem
Existing methods for measuring the distance between a silicon melt and a reflector in a crystal puller suffer from low resolution and accuracy due to thermal expansion and interference from incoherent light emissions, making it difficult to achieve precise HR measurements under vacuum or low-pressure conditions.
Innovation Solution
A non-contact measurement system using a coherent light beam, optical modulator, and detector array to determine the distance by pulsing discrete coherent light beams and filtering with a lock-in amplifier, allowing for precise HR measurement without direct contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical sensors and detector arrays are used to measure distance within the crystal puller, then measurement capability is provided, but resolution and accuracy are reduced due to incoherent light emission from molten or heated materials
Solution Approach 1:
The patent applies periodic action by pulsing the coherent light beam at a specific frequency (e.g., 1000 Hz) and using a lock-in amplifier to detect only signals at this frequency. This periodic modulation allows the system to distinguish the reflected coherent light from the continuous incoherent thermal emission, thereby maintaining measurement precision despite the harmful light interference from the molten silicon.
Solution Approach 2:
The patent introduces an intermediary approach by using a lock-in amplifier as a signal filtering mechanism. This device acts as an intermediary between the detector array and the measurement system, selectively amplifying only the modulated coherent light signal while rejecting the unmodulated incoherent thermal radiation, thus resolving the contradiction between detection capability and light interference.
2Measurement precision
If measurements are made before the puller is brought up to run temperature, then initial distance data is obtained, but the measurements become unusable after thermal expansion occurs
Solution Approach 1:
The patent implements preliminary action by establishing the relationship between the coherent light beam reflection position and the actual distance measurement during a calibration phase at operating temperature. This preliminary calibration creates a reference framework that remains valid throughout the crystal pulling process, allowing continuous accurate measurements despite thermal expansion of components, as the system adapts to the thermal state rather than being disrupted by it.
Solution Approach 2:
The patent applies parameter changes by using the coherent light beam as a reference that does not undergo thermal expansion. The measurement system compensates for thermal expansion of physical components by referencing distances to the optical path, which remains stable. This changes the measurement parameter from physical distance markers that expand thermally to optical path length measurements that are immune to thermal effects.
3Measurement precision
If a coherent light beam is pulsed into discrete beams with a period, then light filtering and measurement precision are improved, but device complexity increases
Solution Approach 1:
The patent applies periodic action by pulsing the coherent light beam at a specific frequency (e.g., 1000 Hz) and using a lock-in amplifier to detect only signals at this frequency. This periodic modulation allows the system to distinguish the reflected coherent light from the continuous incoherent thermal emission, thereby maintaining measurement precision despite the harmful light interference from the molten silicon.
Solution Approach 2:
The patent introduces an intermediary approach by using a lock-in amplifier as a signal filtering mechanism. This device acts as an intermediary between the detector array and the measurement system, selectively amplifying only the modulated coherent light signal while rejecting the unmodulated incoherent thermal radiation, thus resolving the contradiction between detection capability and light interference.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate and reliable HR measurements with improved resolution, enabling precise control of crystal growth processes by determining the distance between the silicon melt and reflector during the pulling process.
Implementation Method 1
a laser to selectively transmit a coherent light beam through the opening to the target object to produce a reflection of the target object on the surface of the silicon melt
Implementation Method 2
an optical modulator to pulse the coherent light beams of the laser into discrete coherent light beams having a period
Implementation Method 3
a lock-in amplifier connected to the detector array to filter discrete coherent light having the period from captured light
Implementation Method 4
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
Data Source
AI summary
A measurement system includes a target object at least partially visible through an opening in a crystal puller. The crystal puller has a silicon melt in a crucible and a reflector defining a central passage through which a crystal is pulled. A detector array captures light through the opening. The detector array is directed to a surface of the silicon melt in the crystal puller and to the target object, and a laser selectively transmits a coherent light beam through the opening to the target object to produce a reflection of the target object on the surface of the silicon melt. An optical modulator pulses the coherent light beams of the laser into discrete coherent light beams having a period, and a lock-in amplifier is connected to the detector array to filter discrete coherent light having the period from captured light.