Semiconductor Foil Casting Exit Slit Pressure Control
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Solution Overview
Problem
Existing semiconductor wafer production methods result in rough top-surfaces due to uncontrolled drag-out of molten silicon during the casting process, requiring subsequent polishing steps.
Innovation Solution
A casting device with a local force exerting means, such as a gas jet generator or conductive coil, is used to increase the outer pressure at the exit slit, reducing the static pressure of the molten semiconductor material and controlling the outflow, thereby minimizing drag-out and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the casting frame exit wall is used to hold-back molten silicon, then the foil thickness can be accommodated, but drag-out of molten silicon occurs causing rough surface
Solution Approach 1:
A gas jet is introduced as an intermediary substance between the molten silicon and the exit wall. The gas jet exerts pressure on the molten silicon to prevent drag-out, while allowing the exit wall to maintain its thickness accommodation function. This mediator resolves the conflict between adaptability and surface quality.
Solution Approach 2:
The invention uses a gas jet (pneumatic means) to exert controlled pressure on the molten silicon at the exit region. This pneumatic approach allows precise control of the molten silicon flow without mechanical contact, preventing surface roughness while maintaining thickness adaptability.
2Device complexity
If no local force is applied at the exit slit, then the device structure is simple, but molten silicon drag-out causes rough surfaces
Solution Approach 1:
Instead of modifying the entire casting frame structure, the invention applies a localized gas jet only at the exit slit region. This local intervention maintains the overall simplicity of the casting frame while precisely addressing the surface roughness problem at the critical exit location.
Solution Approach 2:
The invention changes the pressure parameter of the gas at the exit slit to control the molten silicon flow. By adjusting the gas pressure, the system can prevent drag-out and achieve smooth surfaces without altering the fundamental structure of the casting frame.
3Manufacturing precision
If gas jet is used to increase outer pressure at exit slit, then drag-out is reduced, but device complexity increases
Solution Approach 1:
The gas jet acts as a simple intermediary component that can be added to the existing casting device. It provides the necessary pressure control at the exit slit without requiring complex mechanical modifications to the casting frame structure.
Solution Approach 2:
The invention replaces potential complex mechanical pressure control systems with a simpler gas jet mechanism. This pneumatic approach achieves precise pressure control at the exit slit with minimal device complexity.
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
The solution effectively reduces the drag-out of molten semiconductor material, resulting in smoother semiconductor foils and wafers, eliminating the need for extensive polishing and improving the quality of the crystalline semiconductor foils produced.
Implementation Method 1
the force exerting means comprises a gas jet generator for producing a gas jet with relatively high pressure compared to the ambient pressure at the location of the exit slit; the gas jet generator being arranged for directing the gas jet towards the exit slit
Implementation Method 2
the force exerting means comprises a conductive coil, the conductive coil being located around the casting frame and being adapted for conducting a alternating electric current
Implementation Method 3
the conductive coil and the casting frame are arranged for causing the electromagnetic force to produce an additional pressure at the location of the exit slit to enlarge the outer pressure
Implementation Method 4
the silicon foil starts to grow at the moment (a portion of) the substrate band comes in contact with the molten silicon. During its pass underneath the casting frame in contact with the molten silicon, the silicon wafer grows to its desired thickness
Data Source
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AI summary
A casting device for producing semiconductor material foil includes a casting frame and a substrate band. The casting frame is arranged for holding a molten semiconductor material and includes sidewalls of which an exit sidewall is located at an output position for the semiconductor material foil. The exit side wall is provided with an exit slit. The casting device further includes a local force exerting means to exert at the location of the exit slit a locally enlarged external force on the molten semiconductor material to enlarge an outer pressure on the molten material at the exit slit.