Silica Glass Crucible Uniformity for Silicon Crystal Quality
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Solution Overview
Problem
The existing silica glass crucibles used for pulling silicon crystals suffer from reduced crystallinity due to uneven bubble distribution, non-uniform thickness, and excessive SiO gas generation, leading to brown ring formation and flaking, which lowers the quality of the silicon crystal.
Innovation Solution
A silica glass crucible with controlled circumferential maximum tolerances for bubble content, wall thickness, and transmission, maintained within specific ranges (not more than 6%, preferably 3%, and most preferably 1.5%), ensures uniformity and prevents liquid-level oscillation and flaking, thereby achieving high crystallinity of silicon crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the inner surface of the crucible is brought into contact with the silicon melt at a higher temperature for an extended period of time, then the crystallization rate is improved, but brown rings are generated and flaking portions increase, reducing the crystallinity of the silicon crystal
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure with different functional zones: an inner transparent silica glass layer (5-20 mm thick) that allows light transmission for heating, and an outer opaque silica glass layer containing closed bubbles that prevents excessive heat penetration and reduces SiO gas generation. This localized differentiation of material properties across the crucible thickness enables high crystallization rate while preventing brown ring formation and maintaining crystal quality.
2Ease of manufacture
If the bubble content and transmission in the circumferential direction of the crucible are non-uniform, then the crucible can be manufactured more easily, but brown rings become unevenly distributed and the crystallinity is reduced
Solution Approach 1:
The patent applies parameter changes by establishing specific quantitative requirements: the transparent silica glass layer must have a thickness of 5-20 mm, the opaque layer must contain closed bubbles with a volume ratio of not more than 0.05%, and the light transmissivity at 240 nm or more must be not less than 70%. These parameter specifications transform the manufacturing process from qualitative to quantitative control, enabling consistent production of crucibles that maintain uniform brown ring distribution and high crystal crystallinity.
3Ease of manufacture
If the thickness of the crucible is non-uniform, then the manufacturing process is simpler, but the crucible form becomes faulty and flaking portions increase
Solution Approach 1:
The patent applies preliminary action by pre-establishing the multi-layer structure with controlled thickness parameters before the crystal pulling process. The inner transparent layer is formed with a specific thickness of 5-20 mm, and the outer opaque layer is formed with closed bubbles incorporated during manufacturing. This preliminary structuring prevents thickness non-uniformity from causing faulty crucible forms and flaking during the high-temperature crystal pulling operation.
4Speed
If SiO gas is generated by reaction between the crucible inner surface and silicon melt, then the crystallization process is accelerated, but the silicon melt is oscillated and the crystallinity is reduced
Solution Approach 1:
The patent applies the intermediary principle by introducing the opaque silica glass layer containing closed bubbles as a mediator between the silicon melt and the external environment. This intermediate layer controls SiO gas generation by limiting excessive heat penetration, thereby preventing melt oscillation while still allowing sufficient heat transfer for crystallization. The closed bubbles act as a buffer that modulates the thermal interaction, maintaining both crystallization rate and melt stability.
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 controlled crucible parameters achieve silicon crystal crystallinity of not less than 80%, preventing liquid-level oscillation and flaking, and maintaining high crystal quality by ensuring uniformity in bubble content, wall thickness, and transmission.
Implementation Method 1
a light transmissivity which is not less than 70 % of the total under a light of 240 nm wave length or more
Implementation Method 2
The pulling of the silicon crystal is carried out by uniformly heating the silicon melt
Implementation Method 3
a seed crystal is immersed in the silicon melt and pulled therefrom
Implementation Method 4
SiO gas is generated by a reaction between the crucible inner surface and the silicon melt
Data Source
Figure 1
AI summary
In a silica glass crucible used for pulling a silicon crystal, a circumferential maximum tolerance of each of bubble content, wall thickness and transmission as measured over a full circumference of the crucible at a same height position is not more than 6%.