Vaporized Dopant Feed for Single-Crystal Silicon Resistivity Stability
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Solution Overview
Problem
Existing methods for producing single crystal silicon ingots face challenges in maintaining resistivity within customer specifications due to dopant segregation, particularly with boron and phosphorous, leading to resistivity fluctuations and potential type-changes in the ingot.
Innovation Solution
An ingot puller apparatus with a dopant injector system that includes a vaporization cup and delivery module to vaporize liquid dopants, allowing counter-doping of the silicon melt multiple times during ingot growth, using readily available and inexpensive dopant sources like boric acid, to maintain high resistivity and extend the length of the ingot within specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dopants are added to control resistivity in the ingot, then resistivity can be adjusted to meet specifications, but dopant segregation causes resistivity fluctuations and type-changes that fall out of specifications
Solution Approach 1:
The system performs preliminary counter-doping by adding compensating dopants to the melt before the problematic dopant accumulates. The controller monitors resistivity and adds opposite-type dopants in advance to prevent resistivity from falling out of specification, rather than waiting for segregation to occur.
Solution Approach 2:
The system implements continuous feedback control by monitoring the resistivity of the growing ingot in real-time and automatically adjusting dopant addition. The controller receives resistivity measurements and dynamically modifies the dopant feed rate to maintain resistivity within specifications, compensating for segregation effects as they occur.
2Productivity
If conventional doping methods are used, then the process is simple, but the ingot length within specifications is limited due to dopant accumulation
Solution Approach 1:
The dopant feed system serves multiple functions: it adds primary dopants for resistivity control, adds compensating counter-dopants to offset segregation, and dynamically adjusts feed rates based on real-time resistivity measurements. This multi-functional approach extends ingot length within specifications while managing the complexity through integrated control.
Solution Approach 2:
The system dynamically changes the dopant feed rate parameter based on real-time resistivity measurements and predicted segregation effects. By adjusting the feed rate as a variable parameter rather than using a constant rate, the system extends the usable ingot length while maintaining resistivity control throughout the growth process.
3Manufacturing precision
If expensive or unavailable dopant sources are used, then resistivity control may be improved, but cost and availability become problematic
Solution Approach 1:
The system uses inexpensive, readily available dopant sources such as gaseous dopants that can be easily introduced and discarded. Rather than relying on expensive long-term dopant supplies, the system uses cheap gaseous dopants that are added as needed and can be rapidly adjusted or removed, maintaining precision while improving ease of manufacture.
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 system effectively controls resistivity fluctuations, prevents type-changes, and increases the efficiency of ingot production by allowing multiple counter-doping, ensuring a larger portion of the ingot meets high resistivity specifications.
Implementation Method 1
The second valve selectively channels the liquid dopant into the vaporization cup and the vaporization cup vaporizes the liquid dopant into a vaporized dopant
Implementation Method 2
The delivery module delivers the vaporized dopant to a surface of the melt
Data Source
AI summary
A method for producing a single crystal silicon ingot includes adding polycrystalline silicon to a crucible disposed within a chamber defined by a housing of an ingot puller apparatus, maintaining the chamber at a first pressure, heating the chamber using radiant heat to melt the polycrystalline silicon and form a silicon melt in the crucible, pulling a single crystal silicon ingot from the silicon melt, channeling a liquid dopant at a second pressure greater than the first pressure into a feed tube positioned in the chamber, vaporizing the liquid dopant into a vaporized dopant by flash evaporation at the first pressure within the feed tube, and directing the vaporized dopant from the feed tube toward a surface of the silicon melt to cause the vaporized dopant to enter the silicon melt as a dopant while pulling the single crystal silicon ingot from the silicon melt.