Silicon Crystal Doping via Heat Shield Nozzles
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Solution Overview
Problem
The production of single silicon crystals doped with n-type dopants faces challenges in achieving uniform dopant distribution and minimizing modifications to the hot zone, leading to potential dislocations due to local spikes in dopant concentration.
Innovation Solution
A method involving a gas stream of gaseous dopant supplied through a tubing system and nozzles positioned on a heat shield surrounding the growing crystal, ensuring uniform distribution and avoiding modifications to the hot zone by subliming dopant outside the pulling chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dopant is supplied by blowing gas stream through tube to melt surface, then dopant distribution uniformity is improved, but modifications to hot zone are required and device complexity increases
Solution Approach 1:
A heat shield is introduced as an intermediary component between the dopant supply system and the melt surface. The heat shield protects the hot zone from direct modification while enabling controlled dopant delivery through its annular channel, thus maintaining hot zone integrity while achieving uniform dopant distribution.
Solution Approach 2:
The dopant supply system is segmented into multiple nozzles arranged in an annular pattern on the heat shield. This segmentation allows uniform distribution of dopant across the melt surface without requiring complex modifications to the hot zone structure, as each nozzle independently contributes to the overall uniform distribution.
2Manufacturing precision
If multiple openings are provided for dopant introduction, then dopant distribution uniformity is improved, but local spikes in dopant concentration may occur triggering dislocations
Solution Approach 1:
The heat shield incorporates an annular channel with nozzles positioned at specific locations to deliver dopant to different zones of the melt surface. This local quality approach ensures that dopant is delivered uniformly across the melt without creating local concentration spikes, thereby preventing dislocations while maintaining distribution uniformity.
Solution Approach 2:
The system monitors dopant concentration and delivery parameters to prevent local spikes that could trigger dislocations. By implementing feedback control, the system maintains optimal dopant distribution uniformity while ensuring reliability by preventing harmful concentration variations.
3Quantity of substance
If solid dopant is sublimed in pulling chamber, then dopant supply is achieved, but hot zone modifications are required increasing device complexity
Solution Approach 1:
The heat shield serves as an intermediary structure that receives gaseous dopant outside the hot zone and delivers it to the melt surface. This approach enables dopant supply without requiring modifications to the hot zone, as the heat shield acts as a buffer between the dopant supply system and the crystal growth environment.
Solution Approach 2:
Dopant is sublimed and prepared as a gas stream before entering the hot zone. This preliminary action allows the dopant to be in the correct state for delivery without requiring hot zone modifications, simplifying the overall device while maintaining effective dopant supply.
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 achieves a uniform dopant distribution, reducing the risk of dislocations and maintaining electrical resistivity below 2 mohmcm in the cylindrical portion of the silicon crystal, while minimizing hot zone modifications.
Implementation Method 1
supplying a gas stream comprising gaseous dopant to a surface of the melt
Implementation Method 2
the gas stream is guided in a tubing system into a pulling chamber and through a heat shield which surrounds the growing single crystal, or along an outer surface of the heat shield
Implementation Method 3
from there through nozzles to the surface of the melt
Implementation Method 4
the solid dopant is sublimed in the pulling chamber and after admixture with a carrier gas is blown to the surface of the melt
Data Source
AI summary
Single crystal silicon cylindrical portions grown by the CZ method and highly doped with one or more n-type dopants so as to have a resistivity of not more than 2 mΩcm are prepared by directing dopant in a gas flow from an external sublimation apparatus into the pulling chamber through or below the heat shield, to the bottom of an annular ring of the heat shield and from there through a plurality of nozzles toward the surface of the melt.