Czochralski Pull-up Speed Control via Dynamic Evaluation Length
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Solution Overview
Problem
Existing methods for manufacturing silicon single crystals using the Czochralski method face challenges in accurately controlling the pull-up speed moving average value, especially under disturbances, leading to difficulties in maintaining high-quality crystal production with reduced crystal defects.
Innovation Solution
A method that sets a target value for the pull-up speed and calculates a corrected value based on actual measured values, adjusting the pull-up length (α+β) according to the crystal diameter's deviation from the target, to ensure the pull-up speed moving average value matches the target, thereby improving controllability and reducing quality dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the pull-up speed is fixed to a constant average value in steady state with minimal fluctuation (±0.02 mm/min), then the average pull-up speed is maintained, but the pull-up speed moving average value cannot be precisely controlled under disturbances
Solution Approach 1:
The patent applies dynamics by making the evaluation pull-up length (α+β) variable rather than fixed. The system dynamically adjusts the length based on actual diameter measurements - extending the evaluation length when diameter deviation is large to improve measurement accuracy, and shortening it when diameter is close to target to enable faster response. This dynamic adjustment resolves the contradiction between maintaining stable average speed and achieving precise moving average control under disturbances.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the actual diameter of the single crystal and using this information to adjust the evaluation pull-up length. The system calculates the difference between actual and target diameter, then modifies the evaluation length accordingly, creating a closed-loop control system that adapts to real-time conditions to maintain both stability and precision.
2Speed
If the evaluation pull-up length is shortened to improve response speed, then the response to diameter changes is faster, but the measurement accuracy of pull-up speed decreases
Solution Approach 1:
The system dynamically adjusts the evaluation pull-up length based on the absolute value of diameter deviation. When |actual diameter - target diameter| is large, the evaluation length is extended to gather more data points for accurate measurement. When the deviation is small, the length is shortened to enable faster response. This dynamic adaptation resolves the trade-off between response speed and measurement accuracy.
Solution Approach 2:
The patent changes the parameter of evaluation pull-up length based on operating conditions (diameter deviation). By adjusting this parameter dynamically, the system optimizes both measurement accuracy and response speed according to the current state of the crystal growth process, avoiding the need to fix the length at a single value that would compromise one or the other.
3Measurement precision
If the evaluation pull-up length is extended to improve measurement accuracy, then the pull-up speed measurement is more accurate, but the response time to diameter changes increases
Solution Approach 1:
The evaluation pull-up length is made dynamic rather than static. The system extends the length when measurement accuracy is prioritized (when diameter deviation is large) and shortens it when response time is critical (when diameter is close to target). This dynamic behavior allows the system to optimize the accuracy-time trade-off based on real-time process conditions.
Solution Approach 2:
The system periodically evaluates the diameter deviation and adjusts the evaluation length accordingly. This periodic reassessment allows the system to switch between long evaluation lengths for accuracy and short evaluation lengths for rapid response, creating a rhythm of adjustment that balances both requirements over time.
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 allows for precise control of both pull-up speed and diameter, enhancing the quality and stability of the silicon single crystal production by dynamically adjusting the pull-up length based on real-time diameter measurements, thus reducing crystal defects and quality dispersion.
Implementation Method 1
growing the silicon single crystal by the Czochralski method
Data Source
AI summary
A target value of a pull-up speed of the single crystal is set in advance before starting pulling-up of the single crystal for every predetermined pull-up length, the pull-up speed moving average value is calculated from actual values of the pull-up speeds measured from a time point that pulling-up of a predetermined length of the single crystal has been started until the current time point, a corrected value of the pull-up speed target value at a current time point is calculated and the single crystal is pulled up on the basis of this corrected value. When α is a past pull-up length and β is a future pull-up length, a pull-up length (α+β) used for calculating the corrected value of the pull-up speed target value is changed with an actual value of the single crystal diameter.