Silicon Crystal Growth Front Shape Control
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Solution Overview
Problem
The Czochralski method for producing silicon single crystals often results in dislocations during separation from the melt, leading to reduced yield and the need for a tail section, which decreases productivity, especially with larger wafer diameters where natural convection causes deformation and dislocations.
Innovation Solution
Applying a horizontal magnetic field with a magnetic flux density between 1000 and 2000 Gauss, reducing the lifting speed of the silicon single crystal to zero, and maintaining a static state until the apparent weight decreases, allowing the growth front to form a convex shape opposite to the pulling direction, enabling successful omission of the tail section and suppressing dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tail section is produced to avoid dislocations during separation, then the occurrence of dislocations is suppressed, but the yield ratio decreases due to the smaller crystal diameter in the tail section
Solution Approach 1:
The patent inverts the conventional approach by making the growth front convex (protruding downward into the melt) instead of concave. This convex shape allows the crystal to be separated without forming a tail section, as the convex front naturally prevents dislocation formation during separation while maintaining the full crystal diameter throughout the usable length.
Solution Approach 2:
The patent changes the geometric parameter of the growth front from the conventional concave shape to a convex shape. This parameter change is achieved by controlling the relative lifting speeds and maintaining a static state, which transforms the interface geometry to eliminate the need for a tail section while preventing dislocations.
2Reliability
If a horizontal magnetic field is applied to suppress dislocations and deformation in large-diameter crystals, then dislocations and deformation are reduced, but the temperature difference between center and periphery decreases, preventing the formation of a downward convex shape at the phase boundary
Solution Approach 1:
The patent introduces dynamic control of the lifting speeds and static holding periods to overcome the static constraint imposed by the magnetic field. By dynamically adjusting the process parameters (lifting speeds, static periods), the system can form the required convex shape even under magnetic field conditions that would otherwise prevent it.
Solution Approach 2:
The patent applies preliminary action by forming the convex shape at the growth front before separation occurs. The multiple static periods allow the convex shape to be established in advance under controlled conditions, ensuring that when separation happens, the crystal is already in the optimal shape to avoid dislocations despite the magnetic field's restraining effect.
3Productivity
If the lifting speed is reduced to form a convex growth front and omit the tail section, then productivity increases, but dislocations may occur during separation if the convex shape is not properly formed
Solution Approach 1:
The patent employs feedback control through multiple lifting speed adjustment stages and static period insertions. The process monitors and responds to the formation of the convex shape by adjusting lifting speeds and inserting static periods as needed, ensuring that the convex shape is properly formed before separation to guarantee both high yield and dislocation-free crystals.
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 suppresses dislocations and deformation, allowing for the successful omission of the tail section and improving the shape and yield of silicon single crystals, even under the influence of a horizontal magnetic field.
Implementation Method 1
application of a horizontal magnetic field to the silicon melt, for the purpose of suppressing dislocations and deformation
Implementation Method 2
a strengthened natural convection current within the crucible due to the increased weight of the silicon melt
Implementation Method 3
immersing a seed crystal in the silicon melt, and pulling up a silicon single crystal by gradually rewinding a wire attached to the seed crystal
Data Source
AI summary
Silicon single crystals having suppressed deformation and dislocations and the successful omission of the tail section are produced by growing the straight-body section of the silicon single crystal under the influence of a horizontal magnetic field with a magnetic flux density at its magnetic center being ≧1000 Gauss, and ≦2000 Gauss, reducing the lifting speed of the silicon single crystal relative to the surface of the melt to 0 mm/minute, maintaining a static state until there is a decrease in the apparent weight of the silicon single crystal, then further maintaining the static state so that the entire growth front of the silicon single crystal forms a convex shape protruding in a direction opposite to the lifting direction of the silicon single crystal, and separating the silicon single crystal from the melt.