Vitreous Silica Crucible Bubble Gradient for Silicon Pulling Stability
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Solution Overview
Problem
Conventional vitreous silica crucibles experience unstable pulling of single-crystal silicon due to melt surface vibration, particularly at the initial stage of pulling, leading to reduced yield and susceptibility to pulling failures, as the bubble content near the melt surface is insufficiently controlled.
Innovation Solution
A vitreous silica crucible with a unique bubble distribution, where the upper end portion has a higher bubble content (0.1 vol% or more) increasing by 0.002 vol% to 0.008 vol% per mm, while the lower portion has less than 0.1 vol%, is manufactured using synthetic fused silica powder with specific particle size and carbon content to suppress melt surface vibration and stabilize the shoulder portion formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the inner surface layer is formed as a transparent glass layer with minimal bubbles through evacuation, then heat transfer efficiency is improved, but melt surface vibration occurs at the initial stage of pulling
Solution Approach 1:
The patent applies local quality by creating different bubble content zones within the inner surface layer: the lower portion has minimal bubbles (<0.1 vol%) for optimal heat transfer, while the upper end portion has controlled bubble content (0.1 vol% or more) to suppress melt surface vibration. This spatial differentiation of material properties resolves the contradiction between heat transfer efficiency and melt surface stability.
2Reliability
If bubble content in the inner surface layer is reduced to eliminate vibration, then melt surface stability is improved, but shoulder portion formation becomes unstable
Solution Approach 1:
The patent differentiates bubble content distribution vertically within the inner surface layer, placing bubbles specifically in the upper end portion that corresponds to the shoulder formation zone. This localized bubble presence stabilizes shoulder portion formation while the lower bubble-free region maintains melt surface stability, resolving the contradiction between these two requirements.
3Ease of manufacture
If uniform bubble distribution is maintained throughout the inner surface layer, then manufacturing simplicity is preserved, but both heat transfer efficiency and melt surface stability deteriorate
Solution Approach 1:
The patent implements non-uniform bubble distribution with a gradient structure: the lower portion has <0.1 vol% bubbles for efficient heat transfer, while the upper end portion has 0.1 vol% or more bubbles for vibration suppression. This localized differentiation optimizes both heat transfer efficiency and melt surface stability, overcoming the limitations of uniform bubble distribution.
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 crucible effectively suppresses melt surface vibration and stabilizes the formation of the shoulder portion, achieving high single-crystal silicon yield by controlling bubble distribution and heat transfer efficiency.
Implementation Method 1
an upper end portion of an inner surface layer of the crucible and a lower portion located below the upper end portion have a different amount of bubbles... the amount of bubbles in the lower portion is less than 0.1 vol% and the amount of bubbles in the upper end portion is 0.1 vol% or more... vibration of the melt surface is suppressed
Implementation Method 2
the outer surface portion of the vitreous silica crucible is formed of a bubble containing layer containing a plurality of bubbles... disperses external radiant heat and uniformly transfers the heat to the inside of a mold
Implementation Method 3
the inner surface portion of the vitreous silica crucible is formed of a transparent glass layer which does not substantially contains bubbles... in contact with the silicon melt
Data Source
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AI summary
A vitreous silica crucible for pulling single-crystal silicon, in which the vibration of a melt surface at the initial stage of the pulling of single-crystal silicon can be suppressed, a shoulder portion of single-crystal silicon can be stably formed, and a high yield of single-crystal silicon can be achieved.