Heat Shielding Member Distance Control in Czochralski Silicon Growth
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Solution Overview
Problem
The precise control of the distance between the lower end surface of a heat shielding member and the surface of the raw material melt in the Czochralski method is challenging due to variations in the melt surface position, leading to inaccuracies in temperature gradient control and defects in silicon single crystals, especially in larger crucibles and during prolonged crystal growth.
Innovation Solution
A method involving a criterion reflector placed inside a concavity on the heat shielding member, with a magnetic field applied to stabilize the melt surface, allowing for precise measurement of the distance using a fixed point observation apparatus, and feedback-controlled movement of the crucible or heat shielding member to maintain a predetermined distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the crystal diameter increases, then the productivity improves, but the position of the melt surface varies widely due to crucible deformation and expansion
Solution Approach 1:
The patent implements a feedback control system where the distance between the heat shielding member lower end surface and the melt surface (DPM) is continuously measured using an optical interferometer. The measurement value is fed back to the control unit, which automatically adjusts the heat shielding member position to maintain the DPM within the target range, thereby compensating for melt surface position variations caused by crucible deformation and expansion during large-diameter crystal growth
Solution Approach 2:
The patent replaces conventional mechanical measurement methods with optical measurement technology. An optical interferometer is used to non-contactively measure the DPM with high precision, avoiding mechanical contact that could interfere with the melt surface or crucible. This optical substitution enables accurate measurement of melt surface position variations without introducing additional mechanical complexity
2Ease of operation
If the distance between the heat shielding member and melt surface is not precisely controlled, then the operation becomes easier, but the temperature gradient control becomes inaccurate leading to crystal defects
Solution Approach 1:
The control unit receives real-time DPM measurement data from the optical interferometer and automatically adjusts the heat shielding member position to maintain the distance within the target range. This closed-loop feedback system eliminates the need for manual positioning and complex operational judgment, making the system easy to operate while ensuring precise temperature gradient control through automatic distance maintenance
Solution Approach 2:
The patent establishes a target DPM range (5-15mm) based on crystal diameter, pulling rate, and temperature gradient requirements. By converting the complex temperature gradient control problem into a simpler distance control problem, the system can maintain optimal temperature gradient conditions through straightforward distance parameter management, improving both ease of operation and control precision
3Device complexity
If conventional measurement methods are used, then the device complexity is low, but the measurement precision of DPM is insufficient
Solution Approach 1:
The patent replaces mechanical measurement systems with optical measurement technology. An optical interferometer uses light interference patterns to non-contactively measure the DPM with high precision. This substitution eliminates mechanical contact, reduces wear and friction, and provides superior measurement accuracy while maintaining relatively simple system structure through the use of standard optical components
Solution Approach 2:
The optical interferometer creates an optical copy or image of the heat shielding member lower end surface to perform non-contact measurement. By using light to create a virtual representation of the measurement target, the system achieves high precision measurement without physical contact, avoiding the limitations of mechanical measurement systems
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
This approach enables stable and precise measurement and control of the distance, resulting in improved temperature gradient control and the production of high-quality, defect-free silicon single crystals with enhanced productivity.
Implementation Method 1
when a silicon single crystal is pulled by the Czochralski method while a magnetic field is applied to the raw material melt
Implementation Method 2
observing a position of a mirror image of the criterion reflector with a fixed point observation apparatus, the mirror image being reflected on the surface of the raw material melt
Data Source
AI summary
A method for measuring a distance between a lower end surface of a heat shielding member including a criterion reflector inside a concavity on the lower end surface and a surface of a raw material melt includes: a silicon single crystal is pulled by the Czochralski method while a magnetic field is applied to the raw material melt in a crucible, measuring the distance between the lower end surface of the heat shielding member and the surface of the raw material melt and observing a position of a mirror image of the criterion reflector with a fixed point observation apparatus; and measuring a movement distance of the mirror image with the apparatus and calculating the distance between the lower end surface of the heat shielding member and the surface of the raw material melt from the movement distance of the image and the measured distance.