Silicon Crystal Pull Speed Curvature Inversion
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Solution Overview
Problem
Existing methods for pulling silicon single crystals from a melt struggle to maintain a narrowly specified oxygen concentration in the cylindrical section, leading to yield losses, especially when the crystal diameter is larger and the cylindrical section is shorter, due to uncontrolled oxygen and dopant incorporation during the conical section phase.
Innovation Solution
Controlling the crystal pull speed to induce a curvature inversion of the growth front in the conical section by reducing and then increasing the pull speed, ensuring the curvature changes from concave to convex, and optimizing the conical section's geometry to achieve the desired oxygen concentration in the cylindrical section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional control measures (gas pressure, gas flow rate, heat shield distance, rotation speed, magnetic field strength) are used to control oxygen concentration, then the oxygen concentration can be influenced, but the oxygen concentration cannot be reliably maintained in the specified range from the start of the cylindrical section, leading to yield loss
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the crystal pull speed during the conical section growth phase. Specifically, the pull speed is reduced to a lower value and then increased again, creating a controlled velocity profile that induces curvature inversion of the growth front. This parameter modification enables reliable oxygen concentration control from the start of the cylindrical section, resolving the reliability issue without sacrificing manufacturing precision.
Solution Approach 2:
The patent implements dynamics by transitioning from static control parameters to dynamic control. The crystal pull speed is no longer constant but varies during the conical section growth, creating a time-dependent velocity profile. This dynamic approach allows the growth front curvature to invert, fundamentally changing the oxygen incorporation behavior and ensuring specification compliance from the beginning of the cylindrical section.
2Productivity
If the diameter of the single crystal is larger and the cylindrical section is shorter, then the productivity increases, but the yield loss becomes more serious due to difficulty in maintaining oxygen concentration specification
Solution Approach 1:
The patent applies preliminary action by controlling the oxygen concentration during the conical section growth phase before the cylindrical section begins. By inducing curvature inversion through dynamic pull speed control in the conical section, the oxygen concentration is pre-adjusted to the desired level, ensuring that the cylindrical section starts with compliant material. This preliminary control eliminates yield loss regardless of crystal size or cylindrical section length.
3Manufacturing precision
If the crystal pull speed is controlled to induce curvature inversion of the growth front, then the oxygen concentration in the cylindrical section can be maintained in the specified range, but the process complexity increases
Solution Approach 1:
The patent modifies the crystal pull speed parameter during conical section growth, reducing it to a lower value and then increasing it again. This parameter change induces curvature inversion of the growth front, which fundamentally alters oxygen incorporation behavior. The controlled parameter modification achieves reliable oxygen concentration specification compliance from the start of the cylindrical section.
Solution Approach 2:
The patent implements periodic action through the velocity profile during conical section growth. The pull speed follows a periodic pattern: reduced to a lower value, then increased again. This periodic velocity variation creates the necessary conditions for curvature inversion, enabling precise oxygen concentration control without requiring complex additional equipment.
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 method significantly reduces yield losses by maintaining the specified oxygen concentration in the cylindrical section, improving the quality of semiconductor wafers by effectively controlling dopant and oxygen distribution during the crystal growth process.
Implementation Method 1
crystallizing the single crystal on the seed crystal by raising the seed crystal from the melt with a crystal pull speed
Data Source
AI summary
The invention relates to a method for pulling a silicon single crystal from a melt which is contained in a crucible, comprising immersion of a seed crystal into the melt; crystallization of the single crystal on the seed crystal by raising the seed crystal from the melt with a crystal pull speed; widening the diameter of the single crystal to a setpoint diameter in a conical section, comprising control of the crystal pull speed in such a way as to induce a curvature inversion of a growth front of the single crystal in the conical section.