Czochralski Crystal Pulling Rate Control via Heat Removal Feedback
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Solution Overview
Problem
The Czochralski method for producing single crystals faces challenges in stabilizing crystal quality due to variations in the ratio of crystal growth rate to temperature gradient, making it difficult to control the pulling rate effectively, especially in multi-pulling methods where multiple crystals are produced from the same crucible, leading to inconsistent defect levels.
Innovation Solution
An apparatus and method that include a chamber with a circulating coolant passage, measuring means for temperature and flow rate, and a calculating means to determine the quantity of heat removed, allowing for precise control of the pulling rate based on the measured heat removal to stabilize crystal quality, enabling the production of defect-free silicon single crystals with a diameter of 200 mm or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pulling rate is increased to improve productivity, then the crystal growth rate increases, but the crystal quality deteriorates due to aggregation defects
Solution Approach 1:
The patent implements a feedback control system that measures the actual crystal quality (specifically aggregation defect levels) and uses this information to adjust the pulling rate. The control unit receives quality evaluation data and modifies the pulling rate accordingly, creating a closed-loop system that balances productivity with crystal quality maintenance.
Solution Approach 2:
The patent dynamically changes the pulling rate parameter based on real-time crystal quality conditions. By adjusting the pulling rate as a variable parameter rather than maintaining a fixed value, the system can optimize crystal growth rate while preventing aggregation defects, resolving the contradiction between productivity and manufacturing precision.
2Manufacturing precision
If the pulling rate is adjusted to stabilize crystal quality, then the defect level decreases, but the productivity is reduced
Solution Approach 1:
The patent employs dynamic adjustment of the pulling rate based on actual crystal quality conditions. Rather than using a static, fixed pulling rate, the system continuously adapts the parameter to maintain optimal crystal quality while maximizing productivity, allowing the system to respond to changing growth conditions.
Solution Approach 2:
The feedback mechanism allows the system to monitor crystal quality (specifically aggregation defect concentration) and adjust the pulling rate in response. This enables the system to maintain high productivity by making data-driven adjustments that prevent quality degradation without unnecessarily reducing the growth rate.
3Productivity
If multiple crystals are produced from the same crucible (multi-pulling method), then the productivity increases, but the crystal quality becomes inconsistent
Solution Approach 1:
The patent implements feedback control that monitors crystal quality parameters throughout the multi-pulling process. The control unit receives quality evaluation data for each crystal and adjusts the pulling rate accordingly, ensuring consistent crystal quality across multiple crystals produced from the same crucible while maintaining high productivity.
Solution Approach 2:
The system performs preliminary quality evaluation and adjustment before each crystal growth phase. By assessing quality parameters in advance and pre-adjusting the pulling rate, the system prevents quality inconsistencies from developing during multi-pulling operations.
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 the accurate correction of the pulling rate, resulting in the production of single crystals with stable crystal quality and improved yield of defect-free silicon single crystals, particularly those with an N-region surface, reducing manufacturing costs and enhancing reproducibility.
Implementation Method 1
a circulating coolant passage (31) in which a circulating coolant for cooling the chamber circulates
Implementation Method 2
a circulating coolant passage (31) in which a circulating coolant for cooling the chamber circulates
Implementation Method 3
a heat generator (7) for heating and melting the polycrystalline raw material
Implementation Method 4
a heat generator (7) for heating and melting the polycrystalline raw material
Implementation Method 5
a silicon single crystal of high purity for use as a semiconductor is grown from a silicon melt
Data Source
AI summary
The present invention provides an apparatus for producing single crystals according to the Czochralski method, the apparatus including a chamber that can be divided into a plurality of chambers; at least one of the plurality of divided chambers having a circulating coolant passage in which a circulating coolant for cooling the chamber circulates; and measuring means that respectively measure an inlet temperature, an outlet temperature, and a circulating coolant flow rate of the circulating coolant in the circulating coolant passage; the apparatus further including a calculating means that calculates a quantity of heat removed from the chamber and/or a proportion of the quantity of removed heat, from the measured values of the inlet temperature, outlet temperature, and circulating coolant flow rate; and a pulling rate control means that controls a pulling rate of the single crystal based on the resulting quantity of removed heat and/or the resulting proportion of the quantity of removed heat. The invention also provides a method for producing single crystals using the apparatus. Thus, an apparatus and a method for producing single crystals are provided for producing single crystals while easily stabilizing the crystal quality.