Heat Shield Geometry for Silicon Crystal Void Suppression
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Solution Overview
Problem
Existing methods for growing silicon single crystals using the Czochalski process fail to completely prevent the incorporation of macroscopic voids, which can lead to economic losses due to undetected defects in silicon wafers, especially in highly doped crystals, as they are difficult to detect and alter other crystal properties when trying to reduce voids.
Innovation Solution
A method involving a heat shield with a specific geometry surrounding the single crystal during pulling, where the internal diameter of the heat shield is at least 55 mm greater than the crystal diameter and the radial width is no more than 20% of the crystal diameter, influencing gas flow to suppress the incorporation of gas bubbles into the crystal without altering other crystal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing methods are used to grow silicon single crystals, then crystal growth is achieved, but macroscopic voids are incorporated into the crystal
Solution Approach 1:
A heat shield is introduced as an intermediary component between the crucible and the single crystal. The heat shield has a specific geometry with a lower end at distance h from the melt surface and creates a gas flow pattern that directs gas outward between the shield and melt, then upward outside the shield. This intermediary structure modifies the gas flow and temperature distribution to prevent void incorporation without directly contacting the crystal or melt.
Solution Approach 2:
The invention changes the geometric parameters of the heat shield system, specifically the distance h between the lower end of the heat shield and the melt surface, and the internal diameter DHS of the heat shield. These parameter changes create optimal gas flow conditions that suppress void formation while maintaining crystal growth quality.
2Object-affected harmful factors
If gas bubbles are driven out by varying crucible rotational speed, then some gas removal is achieved, but void incorporation cannot be completely avoided
Solution Approach 1:
The heat shield serves as a mediator that creates a controlled gas flow environment. The gas flows downward between the crystal and heat shield, then outward between the heat shield lower end and the melt, and finally upward outside the heat shield. This intermediary flow pattern actively transports gas bubbles away from the crystal-melt interface, providing more reliable void prevention than crucible rotation alone.
3Object-affected harmful factors
If pressure is reduced during crystal pulling to degas the melt, then gas bubble formation is reduced, but other crystal properties such as oxygen content and gettering capability are altered
Solution Approach 1:
The heat shield creates localized gas flow conditions specifically at the crystal-melt interface region without requiring global pressure changes. The gas flow is concentrated in the region between the heat shield and melt, providing targeted degassing action while maintaining the overall chamber pressure and its associated benefits for crystal composition stability.
4Productivity
If heat shield dimensions are not optimized, then crystal growth is maintained, but gas flow patterns do not effectively suppress void incorporation
Solution Approach 1:
The invention optimizes specific geometric parameters of the heat shield: the distance h from the lower end to the melt surface, and the internal diameter DHS of the heat shield. These parameter changes create the optimal gas flow pattern that suppresses void incorporation while maintaining crystal growth productivity. The lower end of the heat shield is positioned at a specific distance h from the melt surface, and the internal diameter DHS is set to specific values to achieve the desired flow characteristics.
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 method significantly reduces the frequency of macroscopic voids in silicon single crystals, particularly in highly doped crystals, without affecting other crystal properties, ensuring higher quality wafers for electronic components production.
Implementation Method 1
a gas flows downward in the region between the single crystal and the heat shield, outward between the lower end of the heat shield and the silicon melt and then upward again in the region outside the heat shield
Data Source
AI summary
Silicon single crystals are pulled from a melt in a crucible, the single crystal surrounded by a heat shield, the lower end of which is a distance h from the melt surface, wherein gas flows downward between the single crystal and the heat shield, outward between the lower end of the heat shield and the melt, and then upward in the region outside the heat shield. The internal diameter of the heat shield at its lower end is 55 mm or more than the diameter of the single crystal, and the radial width of the heat shield at its lower end is not more than 20% of the diameter of the single crystal. Highly doped single crystals pulled accordingly have a void concentration ≤50 m−3.