Jacket Heater for Flat Phase Boundary in Silicon Crystal Growth
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Solution Overview
Problem
Current methods for producing large single- or multicrystalline material blanks, such as multicrystalline silicon for photovoltaics, face challenges including high etching pit density due to non-flat phase boundaries, inefficient use of silicon ingots, and significant waste generation from rectangular solar cell production, which are exacerbated by thermal stresses and heat loss issues in crucible designs.
Innovation Solution
A device with a single-zone jacket heater that creates a temperature gradient in the crucible by varying heating power from top to bottom, ensuring a flat phase boundary and reducing radial heat flow, allowing for larger silicon ingots with reduced waste and improved thermal efficiency, using a crucible with a polygonal cross-section and meandering heating elements to maintain isothermal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a point-shaped heat sink is used on the crucible bottom, then heat flow from top to bottom is achieved, but the phase boundary becomes non-flat and etching pit density increases
Solution Approach 1:
The heat sink is segmented from a point-shaped configuration into an extended planar structure at the crucible bottom. This segmentation distributes the heat extraction across multiple locations, enabling the formation of a flat phase boundary while maintaining effective heat flow from top to bottom through the molten silicon.
Solution Approach 2:
The heat sink configuration transitions from a zero-dimensional point to a two-dimensional planar structure at the crucible bottom. This dimensional change allows heat to be extracted across a broader area, creating the necessary flat phase boundary geometry for columnar crystal growth while preserving vertical heat flow.
2Productivity
If the crucible base area is increased to produce larger silicon ingots, then waste from rectangular solar cell production is reduced, but thermal insulation requirements and energy loss increase
Solution Approach 1:
The crucible is designed with an asymmetric configuration where the base area is significantly larger than the opening area. This asymmetric geometry allows the crucible to accommodate large silicon ingots that minimize waste when cut into rectangular solar cells, while the narrower opening reduces the surface area exposed to the environment, thereby decreasing thermal energy loss and insulation requirements.
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 results in lower etching pit density, increased ingot size, and cost-effectiveness by optimizing the use of silicon, reducing thermal insulation needs, and minimizing waste, while maintaining high-quality crystal growth with reduced crystal defects.
Implementation Method 1
the heating device and/or thermal insulation of the device is designed to form a temperature gradient in the longitudinal direction in the crucible
Implementation Method 2
To realize heat flow from top to bottom
Implementation Method 3
the heating device has a flat heating element (hereinafter referred to as a "jacket heater") for suppressing a heat flow perpendicular to the longitudinal direction
Implementation Method 4
a meandering course in the longitudinal direction of the crucible or perpendicular thereto
Implementation Method 5
a device for growing crystals... in which a crucible is formed with two-layer walls so that the silicon melt does not come into direct contact
Implementation Method 6
All known manufacturing processes in which a large amount of liquid silicon solidifies into an ingot
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
The invention relates to a device and a method for producing mono- or polycrystalline materials using the vertical gradient freeze process, in particular silicon for photovoltaic applications. According to the invention, minimal material waste is achieved by using a polygonal, particularly rectangular or square, cross-section for the crucible. A planar heating element, in particular a jacket heater, is provided around the circumference of the crucible, generating an inhomogeneous temperature profile. This corresponds to the temperature gradient formed in the center of the crucible. The heating power of the planar heating element decreases from the top to the bottom of the crucible. The planar heating element consists of a plurality of parallel heating elements that extend vertically or horizontally in a meandering pattern. The heating power of the elements is adjusted by varying the conductor cross-section.To prevent localized overheating at the corners of the crucible, cross-sectional constrictions are provided at the reversal points of the meandering course of the ribs. The planar heating element can be formed from a plurality of interconnected individual segments.