Seed Chuck Doping Apparatus for Uniform Silicon Resistivity
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Solution Overview
Problem
The use of volatile dopants in the Czochralski method for growing semiconductor or solar-grade crystals results in significant dopant loss due to evaporation, leading to a non-uniform resistivity profile and the formation of a high resistivity transient region at the seed end of the crystal, which is not usable and increases production costs.
Innovation Solution
A doping apparatus that includes a seed chuck, a seed crystal, and dopant containers connected to the seed chuck, allowing for direct introduction of liquefied dopants into the inner melt zone, enabling rapid initiation of crystal growth and precise control of dopant concentration, thereby reducing or eliminating the high resistivity transient region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If volatile dopants are added to the outer melt zone prior to crystal growth initiation, then dopant loss due to evaporation is reduced, but the high resistivity transient region at the seed end increases
Solution Approach 1:
The invention extracts the dopant addition location from the outer melt zone and relocates it directly to the inner melt zone at the crystal-melt interface. This is achieved by connecting the dopant container to the seed chuck, positioning it precisely where dopant is most needed, thereby eliminating the transport delay and physical flow dependency that cause the high resistivity transient region.
Solution Approach 2:
The seed chuck serves as an intermediary device that simultaneously holds both the seed crystal and the dopant container. This intermediary structure enables direct dopant delivery to the crystal growth interface without requiring dopant transport through the melt, thus resolving the contradiction between reducing dopant loss and maintaining uniform dopant distribution.
2Stability of the object's composition
If dopant is added to the outer melt zone, then dopant can be introduced without disturbing the inner melt zone, but dopant diffusion to the inner melt zone is slow resulting in non-uniform dopant distribution
Solution Approach 1:
The invention performs preliminary action by positioning the dopant container at the inner melt zone interface before crystal growth begins. The dopant is pre-positioned exactly where it needs to be incorporated, eliminating the need for slow diffusion processes and ensuring immediate, uniform dopant distribution in the growing crystal.
Solution Approach 2:
The invention changes the spatial dimension of dopant delivery from radial addition at the outer melt zone to direct vertical addition at the crystal-melt interface. This dimensional change allows dopant to be introduced directly into the growth path of the crystal, achieving uniform distribution without relying on melt convection or diffusion.
3Loss of substance
If dopant is added just prior to crystal growth initiation, then evaporation losses are reduced, but the initial portion of the crystal has lower dopant concentration
Solution Approach 1:
The invention extracts the dopant from the outer melt zone reservoir and repositions it directly at the crystal-melt interface through the seed chuck connection. This extraction eliminates the time delay and transport path that cause dopant depletion at the seed end, ensuring uniform dopant concentration throughout the crystal while maintaining reduced evaporation losses.
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 significantly reduces the length of the high resistivity transient region, enhancing the usability of the ingot and reducing production costs by ensuring a more uniform dopant distribution throughout the crystal, as demonstrated by the comparison of indium-doped silicon ingots grown with and without the doping apparatus.
Implementation Method 1
due to the volatile nature of such dopants, a significant amount of dopant may be lost to evaporation during the process
Implementation Method 2
The puller then lowers a seed crystal into the melt and slowly raises the seed crystal out of the melt. As the seed crystal is grown from the melt, solid polysilicon or liquid silicon is added to the melt to replenish the silicon that is incorporated into the growing crystal.
Data Source
AI summary
An apparatus for doping a melt of semiconductor or solar-grade material is provided. The apparatus includes a seed chuck, a seed crystal connected to the seed chuck, and a dopant container connected to the seed chuck. The seed chuck defines a first end of the apparatus, and the seed crystal defines a second end of the apparatus. The seed crystal is configured to initiate crystal growth when placed in contact with the melt. The dopant container is positioned between the first end and the second end of the apparatus, and defines a reservoir for holding dopant therein. The dopant container is configured to dispense liquid dopant into the melt when positioned proximate the melt. The dopant container and the seed crystal are connected to the seed chuck simultaneously.