Heavily Doped Monocrystalline Silicon Growth with Thin-Neck Gas Purging
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Solution Overview
Problem
Existing methods for producing highly doped monocrystalline silicon rods using the Czochralski process face issues with dislocations due to the evaporation of volatile dopants like phosphorus and arsenic, leading to the formation of oxide particles that act as heterogeneous nucleation sites, especially during the initial cone formation phase.
Innovation Solution
A second flushing gas, preferably argon, is used to purge the area around the thin neck during the crystal growth process, particularly during the transition from the thin neck to the initial cone phase, to prevent the transport of dopants and oxygen, thereby reducing dislocation formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large amount of volatile dopant (phosphorus or arsenic) is added to achieve low resistivity (less than 2 mOhmcm), then the desired electrical properties are improved, but dislocations occur due to oxide particle formation from uncontrolled evaporation
Solution Approach 1:
A gas flow (inert or reducing atmosphere) is introduced as an intermediary between the volatile dopant source and the melt environment. This gas flow captures and transports evaporated dopant species directly to the crystal growth interface, preventing their oxidation into harmful particles while maintaining controlled doping levels in the final crystal
Solution Approach 2:
The patent employs an inert or reducing gas atmosphere in the crystal growth chamber to prevent oxidation of evaporated dopant species. This controlled atmosphere environment eliminates the formation of oxide particles that would otherwise act as nucleation sites for dislocations, while still allowing controlled dopant incorporation into the crystal
2Ease of manufacture
If dopant is introduced from a hopper located several meters above the melt level, then the doping process is simplified, but volatile dopants evaporate uncontrollably and form oxide particles that cause dislocations
Solution Approach 1:
The patent uses gas flow (pneumatic) transport to deliver dopant material from the charge to the melt interface. A controlled gas stream carries volatile dopant species through the growth chamber, enabling precise delivery without uncontrolled evaporation or particle formation, while maintaining the simplicity of the doping process
3Manufacturing precision
If the crystal lift rate and interface temperature are controlled to grow a single crystal, then monocrystalline structure is achieved, but highly doped melts still produce dislocations during initial cone formation
Solution Approach 1:
The patent applies preliminary action by establishing a controlled gas flow environment before and during the critical initial cone formation phase. The gas flow is pre-configured to capture dopant evaporation and deliver it controllably to the interface, preventing oxide particle formation before dislocations can nucleate during the vulnerable initial growth stage
Data Source
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AI summary
A method for pulling a silicon crystal having a resistance of less than 2 mOhmcm according to the Czochralski method, comprising the steps of bringing a seed crystal (102) into contact with a doped silicon melt (105) in a crystal pulling system, wherein the interior of the crystal pulling system is purged with a first purge gas; pulling a thin neck (103) comprising reducing the diameter of the seed crystal (102); expanding the diameter of the thin neck (103) to an initial cone (104) up to a target diameter; and pulling a cylindrical part of the crystal with the target diameter, characterized in that during the pulling of the thin neck, the gas space around the thin neck (103) is purged with a second purge gas at a distance E of more than 2 cm normal to the surface of the thin neck (103).