Silicon Crystal Pulling Rate Control via Melt Surface Distance Measurement
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Solution Overview
Problem
Existing methods for manufacturing silicon single crystals using the Czochralski method face challenges in accurately controlling the crystallization temperature gradient and melt surface level, leading to defects such as ring-like oxidation induced stacking faults and void defects, due to inaccuracies in measuring the melt surface position and crucible deformation during the pulling process.
Innovation Solution
A method that involves measuring the distance between the silicon melt surface and a heat shielding member, using image data to identify the central position of a high intensity band at the solid-liquid interface, and adjusting the crucible level to maintain a constant melt surface position relative to the heater, thereby controlling the crystallization temperature gradients and pulling rate to achieve a desired defect-free region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the pulling rate is gradually lowered to control the V/G value, then the crystallization temperature gradient is improved, but ring-like oxidation induced stacking faults and other defects appear in the crystal structure
Solution Approach 1:
The patent implements dynamic control of the pulling rate based on real-time measurement of the melt surface level. The pulling rate is adjusted according to the distance between the melt surface and the heat shielding member, allowing the system to adapt to changing conditions during crystal growth. This dynamic adjustment prevents the formation of defects by maintaining optimal V/G values throughout the process.
Solution Approach 2:
The patent employs a feedback mechanism where the melt surface level is continuously measured using an imaging device, and the pulling rate is adjusted based on this measurement. The control unit receives the measured distance and modifies the pulling rate accordingly, creating a closed-loop control system that maintains precise temperature gradient control and prevents defect formation.
2Stability of the object's composition
If the melt surface level is not accurately controlled, then the crystallization temperature gradient becomes unstable, but this leads to void defects and inconsistent crystal diameter
Solution Approach 1:
The patent uses a feedback control system where the melt surface level is continuously monitored by an imaging device, and the pulling rate is adjusted based on the measured distance from the melt surface to the heat shielding member. This feedback mechanism ensures stable temperature gradient and consistent crystal diameter by compensating for fluctuations in real-time.
Solution Approach 2:
The patent replaces traditional mechanical level measurement methods with an imaging-based optical measurement system. The imaging device captures images of the melt surface, and image processing algorithms determine the melt surface level, providing more accurate and stable measurements compared to mechanical sensors.
3Reliability
If the crucible level is not adjusted during the pulling process, then the melt surface position drifts, but this causes inaccuracies in temperature gradient control and crystal quality degradation
Solution Approach 1:
The patent implements a feedback control system where the melt surface level is continuously measured by an imaging device, and the pulling rate is adjusted based on the measured distance. This feedback mechanism compensates for melt surface position drift, maintaining accurate temperature gradient control and high crystal quality throughout the growth process.
Solution Approach 2:
The patent performs preliminary calibration to establish the relationship between the measured distance and the actual melt surface level. This preliminary action enables accurate real-time control by providing a reference framework for interpreting measurements and making appropriate adjustments during the pulling process.
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 the V/G value, resulting in high-quality silicon single crystals with a defect-free region and consistent diameter, stabilizing the production process by maintaining the melt surface position and optimizing temperature gradients.
Implementation Method 1
polysilicon is melted in a crucible to form a silicon melt
Implementation Method 2
a heat shielding member disposed so as to partially cover the melt surface
Implementation Method 3
the seed crystal is then pulled upward at a predetermined rotational speed and a predetermined pulling rate, thereby growing a cylindrical silicon single crystal
Data Source
AI summary
In this method for manufacturing a silicon single crystal, when growing the silicon single crystal, in order to control the V/G value with high accuracy so as to yield a desired defect-free region, it is important to conduct the pulling at a constant pulling rate. In the method for pulling a silicon single crystal in the present invention, in order to control the V/G value with high accuracy, the distance Δt between the melt surface of the silicon melt and the heat shielding member that is disposed so as to oppose to and to partially cover this melt surface is continuously measured while pulling (growing) the silicon single crystal.