Offset Heat Shield for Stable Single-Crystal Silicon Growth
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Solution Overview
Problem
Existing methods for controlling convection modes in the Czochralski method for growing monocrystalline silicon fail to reliably fix the convection mode, leading to inconsistent oxygen concentrations and difficulties in growing monocrystals, such as crystal twisting and reduced yield.
Innovation Solution
A monocrystal pull-up apparatus with a heat shield arranged such that its center axis is displaced from the crucible's rotation center axis, creating a non-uniform gap distance for the inert gas flow, allowing control of the convection mode and oxygen concentration by adjusting the heat shield's displacement and ratio of surface areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flow speed of inert gas is changed locally to fix the convection mode, then variation in oxygen concentration is reduced, but the convection mode may not be reliably fixed and crystal twisting may occur
Solution Approach 1:
The heat shield is designed with an asymmetric structure featuring a large opening on one side and a small opening on the other side. This asymmetric configuration creates non-uniform inert gas flow across the silicon melt surface, which reliably fixes the convection mode to a single direction (either clockwise or counterclockwise) while maintaining crystal uniformity by avoiding the crystal twisting problems associated with local flow changes
2Reliability
If the heat shield effect is made uneven in the circumferential direction to fix the convection mode, then oxygen concentration variation is reduced, but temperature distribution becomes large causing crystal twisting
Solution Approach 1:
The heat shield incorporates local quality variations through its asymmetric opening design, where different regions of the heat shield have different opening sizes. This creates localized differences in inert gas flow and heat shield effects that are sufficient to fix the convection mode while maintaining overall temperature distribution uniformity across the crystal growth region, thereby preventing crystal twisting
3Temperature
If the center axis of the heat shield is aligned with the rotation center axis of the crucible, then uniform temperature distribution is maintained, but the convection mode cannot be fixed and oxygen concentration varies
Solution Approach 1:
The heat shield is deliberately positioned with its center axis displaced from the rotation center axis of the crucible, creating an asymmetric arrangement. This asymmetric positioning generates non-uniform inert gas flow patterns that fix the convection mode to a single direction, thereby stabilizing oxygen concentration in the monocrystalline silicon while the heat shield still provides sufficient thermal protection to maintain acceptable temperature distribution uniformity
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 stabilizes the convection mode and oxygen concentration, enabling consistent growth of monocrystalline silicon with controlled oxygen levels, reducing crystal defects and improving yield.
Implementation Method 1
When a horizontal magnetic field is applied to a silicon melt using the MCZ method, either one of convection modes is initially formed
Implementation Method 2
The formed convection mode is at random either the clockwise vortex mode or the counterclockwise vortex mode
Data Source
AI summary
There is provided a method for growing monocrystalline silicon using a monocrystal pull-up apparatus that includes: a chamber; a crucible where silicon melt is stored; a heater configured to heat the silicon melt; a heat shield arranged above the crucible in a manner to surround monocrystalline silicon pulled up from the silicon melt; and an inert gas supply unit configured to supply an inert gas to pass through between the monocrystalline silicon and the heat shield, the method including: pulling up the monocrystalline silicon while applying a horizontal magnetic field to the silicon melt, in which the heat shield is arranged such that a center axis thereof vertically passing through a center position of an opening of the heat shield is displaced from a vertical rotation center axis of the crucible in a direction different from a magnetic-field application direction in a magnetic-field center portion of the horizontal magnetic field.