Monocrystalline Silicon Crystal Puller With Dynamic Heat Shield Gap Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Czochralski process faces challenges in maintaining the diameter of silicon crystals with uniformity and preventing defect formation due to variations in pull-speed, which affect the quality and yield of semiconductor wafers.
Innovation Solution
A crystal puller apparatus and computer-implemented methods are used to control the pull-speed and temperature gradient by adjusting the gap between a heat shield and the silicon melt, maintaining the Voronkov ratio within the Pv-Pi margin to achieve a defect-free crystal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pull-speed of the crystal seed is increased to improve productivity, then the crystal growth rate increases, but the crystal diameter decreases and uniformity deteriorates
Solution Approach 1:
The patent applies dynamics by making the heat shield position adjustable during the crystal growth process. The heat shield can be dynamically repositioned along the vertical axis to change the gap between the heat shield and silicon melt surface, thereby dynamically adjusting the temperature gradient to compensate for diameter changes caused by varying pull speeds
Solution Approach 2:
The patent changes physical parameters by adjusting the gap distance between the heat shield and silicon melt surface. This parameter change directly affects the temperature gradient at the solid-liquid interface, allowing control over crystal diameter while maintaining high pull speeds for improved productivity
2Manufacturing precision
If the pull-speed is decreased to maintain crystal diameter uniformity, then manufacturing precision improves, but productivity decreases
Solution Approach 1:
The patent changes the temperature gradient parameter by adjusting the heat shield position. By increasing the temperature gradient (decreasing the gap), the crystal diameter is reduced, allowing faster pull speeds to produce uniform diameter crystals, thereby maintaining productivity while achieving precision
Solution Approach 2:
The heat shield acts as an intermediary element between the heating system and the silicon melt. By adjusting its position, it mediates the heat transfer to the melt, controlling the temperature gradient and enabling independent optimization of pull speed and diameter uniformity
3Manufacturing precision
If a sophisticated feedback control system is introduced to control crystal diameter, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The heat shield serves as a simple mechanical intermediary that directly controls the temperature gradient through position adjustment. This mechanical approach is simpler than complex thermal control systems with multiple heaters and sensors, reducing device complexity while achieving diameter control
Solution Approach 2:
The patent controls crystal diameter by changing a single physical parameter - the heat shield position - rather than using complex feedback control of multiple parameters. This single-parameter control approach simplifies the control system while maintaining manufacturing precision
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 ensures the production of defect-free silicon crystals by controlling the Voronkov ratio, thereby improving the quality and yield of silicon wafers for semiconductor applications.
Implementation Method 1
a heat shield above a surface of the silicon melt; a lifter to change a gap between the heat shield and the surface of the silicon melt
Implementation Method 2
rotationally pulling a crystal seed from the surface of the silicon melt. As the crystal seed is being pulled from the silicon melt, monocrystalline silicon extends from the crystal seed and forms a cylindrical crystal
Data Source
AI summary
A crystal puller apparatus comprises a pulling assembly to pull a crystal from a silicon melt at a pull speed; a crucible that contains the silicon melt; a heat shield above a surface of the silicon melt; a lifter to change a gap between the heat shield and the surface of the silicon melt; and one or more computing devices to determine an adjustment to the gap using a Pv-Pi margin, at a given length of the crystal, in response to a change in the pull speed. The computer-implemented method by a computing device comprises determining a pull-speed command signal to control a diameter of the crystal; determining a lifter command signal to control a gap between a heat shield and a surface of a silicon melt from which the crystal is grown; and determining an adjustment to the gap, in response to a different pull-speed, using a Pv-Pi margin.