Uniform Silicon Ingot Doping via Segmented Crucible Convection
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Solution Overview
Problem
The Czochralski method for growing crystalline silicon ingots faces challenges in achieving axially uniform dopant concentration due to segregation effects, particularly in continuous processes where dopant resupply is difficult, especially for dopants like gallium with low melting points and high segregation coefficients, leading to non-uniformity and increased costs from sorting steps.
Innovation Solution
A method involving a crucible with an inner growth zone in fluid communication with an outer feed zone, where initial charges of silicon and dopant are pre-loaded, allowing for the growth of ingots with axially constant dopant concentration by controlling crucible geometry and feed rates, eliminating the need for continuous dopant resupply during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous Czochralski process is used to increase productivity, then manufacturing throughput increases, but dopant concentration uniformity deteriorates due to segregation effects and difficulty in continuous dopant resupply
Solution Approach 1:
The crucible is divided into two distinct zones: an inner growth zone where crystallization occurs and an outer feed zone where dopant-containing silicon is stored. This segmentation allows the dopant to be pre-loaded in the feed zone, eliminating the need for continuous resupply during growth and maintaining uniform dopant concentration throughout the ingot while enabling continuous production.
Solution Approach 2:
The dopant material is pre-loaded into the outer feed zone together with silicon feedstock before the growth process begins. This preliminary action ensures that the dopant is already positioned and ready to be transported to the growth zone through melt convection, avoiding the need for continuous dopant resupply and ensuring uniform distribution throughout the growing crystal.
2Ease of manufacture
If dopant is charged into the crucible with silicon feedstock, then the process is simplified, but segregation effects cause non-uniform dopant distribution in the grown ingot
Solution Approach 1:
Different regions of the crucible are assigned different functions: the inner growth zone receives controlled dopant delivery for uniform crystal growth, while the outer feed zone stores excess dopant-containing silicon feedstock. This local differentiation ensures that dopant is supplied at the correct rate to the growth zone, maintaining axial uniformity while keeping the overall process simple.
Solution Approach 2:
The system utilizes natural melt convection as a feedback mechanism to transport dopant from the outer feed zone to the inner growth zone. The convection current automatically regulates dopant supply based on the growth conditions, ensuring uniform dopant distribution without requiring complex external control systems.
3Manufacturing precision
If dopant resupply is performed during growth, then dopant concentration can be maintained, but device complexity increases due to continuous feeding requirements
Solution Approach 1:
The outer feed zone acts as a self-service reservoir that automatically supplies dopant to the inner growth zone through natural melt convection. The system requires no external intervention or complex feeding mechanisms during growth, as the dopant is self-regulated by the convective flow patterns in the melt, simplifying the overall device while maintaining precise dopant control.
4Manufacturing precision
If batch Czochralski process is used to achieve uniform dopant distribution, then dopant uniformity is improved, but productivity decreases due to crucible replacement requirements
Solution Approach 1:
By segmenting the crucible into growth and feed zones, the system enables continuous operation where the feed zone continuously replenishes the growth zone. This eliminates the need to replace the entire crucible after each batch, allowing multiple ingots to be grown from a single loaded crucible while maintaining uniform dopant distribution through the segmented architecture.
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 silicon ingots with uniform dopant concentration and resistivity, reducing manufacturing costs and complexity by maintaining consistent dopant levels along the ingot length without the need for continuous dopant replenishment, thus improving the efficiency and uniformity of silicon wafer production.
Implementation Method 1
The inner growth zone and the outer feed zone have upper melt surfaces at substantially similar heights
Implementation Method 2
melting the silicon and dopant material in the inner growth zone to form a melted mixture
Implementation Method 3
growing the silicon ingot from the inner growth zone
Data Source
AI summary
The present invention relates to a method of growing a silicon ingot comprising a dopant material having a segregation coefficient of k, wherein the concentration of the dopant is axially substantially uniform throughout the ingot. The method comprises the steps of providing a crucible having an inner growth zone in fluid communication with an outer feed zone, and the inner growth zone and the outer feed zone have cross-sectional areas that are can be used to determine conditions for maintaining dopant uniformity for the specific dopant material used. A crystalline growth system for growing at least one uniformly doped silicon ingot is also disclosed.