Doped Silicon Crystal Resistivity Control via Precise Dopant Model
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Solution Overview
Problem
The challenge in growing silicon single crystal ingots doped with gallium, indium, or aluminum is achieving uniform resistivity due to segregation and dopant migration issues, particularly in continuous Czochralski processes, which affects the efficiency and cost-effectiveness of photovoltaic device production.
Innovation Solution
A method using a control system that calculates and controls dopant additions based on a doping model, incorporating a sacrificial vessel for inter-ingot doping and precise dopant containers to maintain uniform resistivity, and utilizing a CCZ apparatus with a large crucible configuration to minimize evaporation and segregation, ensuring consistent dopant concentration and resistivity across the ingot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous Czochralski process is used to grow silicon single crystal ingots, then productivity is improved, but dopant concentration uniformity deteriorates due to segregation and dopant migration
Solution Approach 1:
The patent applies preliminary action by pre-calculating the required dopant additions using a doping model that accounts for segregation and evaporation effects before crystal growth begins. The control system uses this model to determine precise dopant addition amounts at each stage, preventing uniformity issues rather than correcting them afterward. This allows continuous growth while maintaining dopant concentration control.
Solution Approach 2:
The patent implements feedback control by continuously monitoring actual dopant concentration during crystal growth and comparing it with target values from the doping model. The control system adjusts dopant addition rates in real-time based on deviations detected, compensating for segregation effects and maintaining uniform dopant distribution throughout the continuously grown crystal ingot.
2Quantity of substance
If dopant addition is increased to compensate for segregation, then dopant concentration in crystal is improved, but dopant loss through evaporation increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the dopant addition rate based on process conditions such as melt temperature, crystal growth rate, and ambient pressure. The doping model calculates optimal dopant addition parameters that compensate for segregation while minimizing evaporation losses. The control system modifies these parameters in real-time to maintain dopant concentration uniformity without excessive dopant loss.
3Manufacturing precision
If batch CZ process is used to maintain dopant uniformity, then manufacturing precision is improved, but productivity deteriorates
Solution Approach 1:
The patent applies continuity of useful action by enabling continuous crystal growth without the interruptions inherent in batch processing. The doping model and control system maintain dopant concentration uniformity throughout continuous growth by calculating and adjusting dopant additions in real-time. This eliminates the need to stop and restart between batches while preserving dopant uniformity, thereby maintaining both productivity and 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
The method achieves silicon single crystal ingots with resistivity variation less than 10% radially and axially, enhancing the production of photovoltaic devices by maintaining consistent dopant concentration and reducing the impact of light-induced degradation, thereby improving efficiency and reducing production costs.
Implementation Method 1
A heated crucible holds a melted form of a charge material from which the crystal is to be grown
Implementation Method 2
When the seed is lowered into the melt material, it causes a local decrease in melt temperature, which results in a portion of the melt material crystallizing around and below the seed
Implementation Method 3
After the doped silicon is melted and crystal growth has begun, the dopant concentration increases in the melt due to rejection of the dopant at the crystal growth interface
Implementation Method 4
dopant evaporation from the melt surface
Data Source
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AI summary
A doped silicon single crystal having a resistivity variation along a longitudinal and/or radial axis of less than 10% and a method of preparing one or a sequential series of doped silicon crystals is disclosed. The method includes providing a melt material comprising silicon into a continuous Czochralski crystal growth apparatus, delivering a dopant, such as gallium, indium, or aluminum, to the melt material, providing a seed crystal into the melt material when the melt material is in molten form, and growing a doped silicon single crystal by withdrawing the seed crystal from the melt material. Additional melt material is provided to the apparatus during the growing step. A doping model for calculating the amount of dopant to be delivered into the melt material during one or more doping events, methods for delivering the dopant, and vessels and containers used to deliver the dopant are also disclosed.