Czochralski Silicon Crystal Pulling Speed and Crucible Rotation Control
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Solution Overview
Problem
Existing methods for producing single-crystal silicon semiconductor wafers, such as the Czochralski process, face challenges in controlling the V/G ratio to minimize light point defects (LPDs) and large etch pits (LPITs), which affect the quality of wafers, particularly in the 75% to 95% rod length range.
Innovation Solution
The method involves maintaining a constant pulling speed for the end cone, rotating the crucible with a significant amplitude in rotational speed before and after direction change, and applying a horizontal magnetic field during the cylindrical section pull, ensuring the pulling speed is greater than 0.46 mm/min and crucible rotation amplitude is not less than 6 rpm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the pulling speed is increased to reduce residence time and minimize defects, then light point defects (LLS) are reduced, but controlling the V/G ratio becomes more difficult
Solution Approach 1:
The patent applies dynamics by continuously adjusting the pulling speed during the crystal pulling process. The pulling speed is increased in the final stage (end cone formation) to reduce residence time and minimize LLS defects, while the adjustment is dynamically coordinated with temperature gradient control to maintain the V/G ratio within the optimal range. This dynamic adjustment allows the system to adapt to different process stages and achieve both defect reduction and precise ratio control.
Solution Approach 2:
The patent utilizes parameter changes by modifying the pulling speed as a key process parameter. Specifically, the pulling speed is increased to at least 0.46 mm/min during end cone formation, which reduces the residence time of silicon in the temperature zone where LLS defects form. This parameter change is implemented while simultaneously managing the temperature gradient to maintain the V/G ratio control, thereby resolving the contradiction between defect reduction and precision control.
2Stability of the object's composition
If the crucible rotation speed is increased to improve mixing and uniformity, then oxygen distribution is improved, but mechanical stability decreases
Solution Approach 1:
The patent applies periodic action by continuously reversing the rotation direction of the crucible during the crystal pulling process. This periodic reversal creates a mixing effect that promotes uniform oxygen distribution in the melt without requiring excessively high rotation speeds. The alternating rotation directions prevent the formation of stable vortex patterns that could compromise crystal structural stability, thereby achieving both compositional uniformity and mechanical stability.
3Ease of operation
If the pulling speed is maintained constant for simplicity, then process control is easier, but end cone shape stability deteriorates
Solution Approach 1:
The patent applies dynamics by implementing a controlled pulling speed adjustment strategy during end cone formation. Rather than maintaining a constant speed, the pulling speed is increased to at least 0.46 mm/min in the final stage, which helps stabilize the end cone shape by reducing residence time and minimizing defects. This dynamic speed adjustment is coordinated with crucible rotation and temperature control to maintain overall process stability while achieving superior end cone quality.
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 significantly reduces light point defects (LLS) to less than 19 nm in the specified rod length range, improving wafer quality by reducing residence time and stabilizing the end cone shape, thereby minimizing dislocations.
Implementation Method 1
The melt is subjected to a horizontal magnetic field, at least during the pulling of the cylindrical section of the single crystal
Implementation Method 2
The single crystal is pulled from the melt by hanging from a seed crystal
Implementation Method 3
the axial temperature gradient G is a measure that indicates the change in temperature at the crystallization boundary in the direction of the crystal lift
Implementation Method 4
rotating the crucible at a rotational speed and in a rotational direction during pulling of the cylindrical section and the end cone of the single crystal
Implementation Method 5
Heat transport, in turn, is significantly influenced by the thermal properties of the environment surrounding the growing single crystal
Data Source
AI summary
The invention relates to a method for producing semiconductor wafers from single-crystal silicon, comprising drawing a cylindrical section and subsequently an end cone of a single silicon crystal from a melt contained in a crucible; wherein the drawing speed during the drawing of the end cone remains essentially constant compared to the drawing speed during the drawing of the cylindrical section end region; rotating the crucible at a rotational speed and in a rotational direction during the drawing of the cylindrical section and the end cone of the single crystal;and the separation of the semiconductor wafers made of single-crystal silicon from the cylindrical section of the single crystal, characterized in that the drawing speed during the drawing of the end cone is at least greater than 0.46 mm/min, the direction of rotation of the crucible is continuously changed and the amplitude of the rotational speed before and after the change of the direction of rotation is not less than 6 rpm.