Low-Pass Filter for Single Crystal Ingot Diameter Control
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Solution Overview
Problem
In the Czochralski method for growing high-quality silicon single crystals, existing systems face challenges in accurately controlling the pull speed, leading to defects such as Flow Pattern Defect, Oxidation-induced Stacking Fault, and Large Dislocation Pit, due to noise interference in diameter measurement data, which affects the quality of semiconductor wafers.
Innovation Solution
A system that includes a diameter measuring sensor, a Low-Pass Filter to remove short period noise from the measured data, and an Automatic Diameter Control sensor to precisely control the pull speed, using noise-removed data for accurate diameter control of the single crystal ingot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a diameter measuring sensor is used to control the pull speed in the Czochralski method, then the diameter control capability is improved, but noise interference in the measured data causes defects such as Flow Pattern Defect, Oxidation-induced Stacking Fault, and Large Dislocation Pit
Solution Approach 1:
The patent applies preliminary action by implementing a low-pass filter before the diameter measurement data is used for pull speed control. The filter pre-processes the raw measurement data to remove noise components, ensuring that only clean, reliable data reaches the control system. This prevents noise-induced defects while maintaining diameter control capability.
Solution Approach 2:
The patent introduces an intermediary element (low-pass filter) between the diameter measuring sensor and the pull speed control system. This intermediary processes the measurement data by filtering out high-frequency noise while preserving the genuine diameter variation signals, thereby mediating between measurement accuracy and control reliability.
2Productivity
If the pull speed is increased to improve productivity, then the production efficiency is improved, but defects such as Flow Pattern Defect and Large Dislocation Pit occur due to excessive pull speed
Solution Approach 1:
The patent implements feedback control by continuously monitoring the filtered diameter measurement data and adjusting the pull speed accordingly. The control system uses the cleaned measurement signals to maintain optimal pull speed, preventing both excessive speed (which causes defects) and unnecessarily slow speed (which reduces productivity).
Solution Approach 2:
The patent dynamically adjusts the pull speed parameter based on the filtered diameter measurements. By using clean, noise-free measurement data, the system can make precise parameter adjustments that optimize both productivity and crystal quality, avoiding the defects associated with improper pull speed.
3Measurement precision
If noise filtering is applied to the diameter measurement data, then the pull speed control accuracy is improved, but the response time to genuine diameter changes may be delayed
Solution Approach 1:
The patent applies local quality by selectively filtering different frequency components of the measurement signal. The low-pass filter removes high-frequency noise while preserving lower-frequency genuine diameter variation signals, maintaining different qualities for different signal components based on their relevance to the control process.
Solution Approach 2:
The patent applies partial filtering action by using a low-pass filter with a carefully selected cutoff frequency. This partial filtering removes only the harmful high-frequency noise components while preserving the useful lower-frequency diameter variation signals, achieving the optimal balance between noise reduction and response time.
Data Source
AI summary
Provides are a system of controlling a diameter of a single crystal ingot and a single crystal ingot growing apparatus including the same. The system of controlling a diameter of a single crystal ingot includes: a diameter measuring sensor measuring a diameter of a single crystal ingot; a Low-Pass Filter (LPF) removing short period noise from measured data from the diameter measuring sensor; and an Automatic Diameter Control (ADC) sensor controlling the diameter of the single crystal ingot through controlling of a pull speed by using data having the noise removed as current data.