Cooler Positioning for Silicon Monocrystal Shoulder Stability
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Solution Overview
Problem
The existing methods for manufacturing low-resistivity silicon monocrystals, particularly for large-diameter discrete semiconductors, face challenges in reducing dislocations at the shoulder region due to unstable temperature distribution and convection issues during the Czochralski process, especially when using a magnetic field to control convection.
Innovation Solution
The method involves controlling the movement of a cooler during the formation of the shoulder by lowering it stepwise and stopping its descent at a specific position above the dopant-added melt to stabilize the temperature distribution, while applying a horizontal magnetic field to manage convection, thereby reducing dislocations in large-diameter low-resistivity silicon monocrystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large-diameter silicon monocrystal is pulled up using conventional CZ process with a cooler positioned close to the melt, then the temperature gradient for crystal growth is maintained, but dislocation occurs at the shoulder region due to unstable temperature distribution
Solution Approach 1:
The cooler is moved from a fixed position to a dynamically adjustable position. During shoulder formation, the cooler is positioned at a first height above the melt surface; during cylindrical region formation, it is moved to a second height closer to the melt surface. This dynamic repositioning stabilizes temperature distribution during critical shoulder formation while maintaining efficient cooling during subsequent growth phases.
Solution Approach 2:
The cooler position is predetermined and adjusted in advance based on the growth phase. Before shoulder formation begins, the cooler is positioned at the appropriate height to ensure stable temperature distribution from the outset, preventing dislocation before it can occur. This preliminary positioning avoids the need for reactive corrections during critical growth phases.
2Productivity
If the cooler is positioned close to the dopant-added melt to maintain temperature gradient, then crystal growth efficiency is improved, but temperature distribution becomes unstable causing abnormal growth at the shoulder
Solution Approach 1:
The cooler's vertical position is dynamically adjusted according to the crystal growth phase. During shoulder formation, it is positioned higher (first height) to stabilize temperature distribution and prevent abnormal growth. During cylindrical region formation, it is moved lower (second height) to maximize cooling efficiency and maintain steep temperature gradients for high-speed growth. This temporal separation of positioning strategies resolves the contradiction between growth efficiency and precision.
Solution Approach 2:
The cooler positioning follows a periodic pattern corresponding to the crystal growth phases. The cooler is systematically moved between two distinct height positions as the crystal transitions from shoulder formation to cylindrical growth. This periodic repositioning ensures that each growth phase receives the optimal cooling conditions, preventing the instability that would occur with continuous close positioning.
3Stability of the object's composition
If a magnetic field is applied to restrain natural convection of silicon melt, then convection control is improved, but the method is not suitable for large-diameter crystals where vigorous convection occurs
Solution Approach 1:
The cooler position acts as an intermediary control mechanism between the heat source (melt) and the crystal growth interface. By adjusting the cooler's distance from the melt surface, the system indirectly controls temperature distribution and thermal gradients without requiring direct intervention in the melt convection patterns. This intermediary approach allows effective control for both small and large-diameter crystals where direct magnetic field control becomes insufficient.
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 effectively reduces abnormal growth and dislocations at the shoulder region, allowing for the production of high-quality low-resistivity silicon monocrystals with reduced defects, even for diameters of 200 mm or more, by maintaining a stable temperature distribution and minimizing heat dissipation.
Implementation Method 1
a magnetic field applying unit disposed outside the chamber and configured to apply a horizontal magnetic field to the dopant-added melt
Implementation Method 2
the natural convection of the silicon melt in the crucible
Implementation Method 3
a cooler disposed above the crucible and configured to cool the silicon monocrystal that is being grown
Implementation Method 4
a pulling-up unit configured to pull up a seed crystal after the seed crystal is in contact with the dopant-added melt
Data Source
AI summary
A manufacturing method of a silicon monocrystal uses a monocrystal pulling-up apparatus including: a chamber; a crucible disposed in the chamber and configured to receive dopant-added melt; a pulling-up portion that pulls up a seed crystal after the seed crystal is in contact with the dopant-added melt; a cooler disposed above the crucible to cool a monocrystal that is being grown; and a magnetic field applying unit disposed outside the chamber to apply a horizontal magnetic field to the dopant-added melt. The method includes: during a formation of a shoulder of the silicon monocrystal, starting the formation while moving the cooler downward; stopping the cooler from moving downward at a stop position before a top of the shoulder reaches a level of a lower end of the cooler; and continuing the formation of the shoulder while the cooler is kept at the stop position.