Czochralski Crystal Pulling Rate Control Without Real-Time Diameter Measurement
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Solution Overview
Problem
The existing methods for pulling single crystals of semiconductor material using the Czochralski method face challenges in controlling the diameter transition from the initial cone to the cylindrical section due to disturbances caused by reflections from the crucible wall, limiting the flexibility in starting the shouldering phase at arbitrary diameters.
Innovation Solution
A method that measures the diameter of the initial cone and calculates its change over time, allowing for open-loop control of the pulling rate to begin shouldering at any arbitrary point in time, with a predetermined profile for the pulling rate and heating power to achieve a target diameter for the cylindrical section, ensuring low concentrations of point defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If closed-loop control of diameter is used during shouldering phase, then diameter control precision is improved, but measurement reliability deteriorates due to bright ring reflection from crucible wall
Solution Approach 1:
The patent applies preliminary action by determining the pulling rate profile in advance through iterative computation before the shouldering phase begins. The pulling rate is predetermined as a function of time based on the initial cone growth characteristics, allowing the transition to cylindrical section at a precisely calculated moment without relying on real-time diameter measurement during the problematic bright ring period.
Solution Approach 2:
The patent replaces the optical measurement system (camera-based diameter measurement) with a computational model-based control system. Instead of measuring diameter directly during shouldering, the system uses pre-computed pulling rate profiles based on initial cone parameters to achieve the transition, substituting mechanical/optical measurement with mathematical prediction.
2Manufacturing precision
If shouldering is begun at predicted diameter only, then manufacturing precision is improved, but adaptability deteriorates because shouldering cannot start at arbitrary diameter
Solution Approach 1:
The patent applies dynamics by making the pulling rate a time-dependent function that can be dynamically adjusted. The iterative computation process allows the system to calculate optimal pulling rate profiles for different scenarios, enabling shouldering to begin at arbitrary diameters while maintaining precision through dynamic adaptation of the pulling rate based on real-time conditions.
3Manufacturing precision
If direct diameter measurement is performed during shouldering, then manufacturing precision is improved, but measurement capability deteriorates due to inability to detect bright/dark transition
Solution Approach 1:
The patent introduces an intermediary computational model that bridges the gap between initial cone growth and cylindrical section formation. Instead of directly measuring the problematic bright ring region, the system uses the measured initial cone parameters as intermediaries to calculate the required pulling rate profile, indirectly achieving precise diameter control without direct measurement of the obscured region.
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
Enables flexible initiation of shouldering at any time and attainment of the target diameter, avoiding yield losses by maintaining optimal axial temperature gradients and point defect concentrations, allowing for continuous pulling of the single crystal.
Implementation Method 1
The term 'meniscus' denotes that part of the melt which rises from the surface of the melt as far as the lower edge of the growing single crystal and which forms on account of surface tension and interfacial tension effects
Implementation Method 2
The term 'meniscus' denotes that part of the melt which rises from the surface of the melt as far as the lower edge of the growing single crystal and which forms on account of surface tension and interfacial tension effects
Implementation Method 3
Glowing hot parts of the relatively close surroundings of the single crystal, such as the crucible wall, for example, are reflected in the meniscus. The reflection of the crucible wall is perceived as a bright ring on a camera recording from the region of the phase boundary between growing single crystal and melt
Data Source
AI summary
Single crystal semiconductor ingots are pulled from a melt contained in a crucible by a method of controlling the pulling the single crystal in a phase in which an initial cone of the single crystal is grown until a phase in which the pulling of a cylindrical section of the single crystal is begun, by measuring the diameter Dcr of the initial cone of the single crystal and calculating the change in the diameter dDcr/dt; pulling the initial cone of the single crystal from the melt at a pulling rate vp(t) from a point in time t1 until a point in time t2, starting from which the pulling of the cylindrical section of the single crystal in conjunction with a target diameter Dcrs is begun, wherein the profile of the pulling rate vp(t) from the point in time t1 until the point in time t2 during the pulling of the initial cone is predetermined by means of an iterative computation process.