Fibrous Activated Carbon Purification of Alkaline Solutions
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Solution Overview
Problem
Existing methods for purifying aqueous alkaline solutions, such as those used for etching silicon wafers, are ineffective in reducing metallic impurities like iron, nickel, and copper to the necessary low levels due to limitations with activated carbon and electrolysis, leading to contamination and poor electrical insulating properties of silicon wafers.
Innovation Solution
The use of fibrous activated carbon, activated with acids like hydrochloric, nitric, or sulfuric acid, to efficiently remove metallic impurities like nickel, iron, and copper from aqueous alkaline solutions, achieving high-purity solutions suitable for etching silicon wafers by continuous passage through columns with specific surface areas and pore volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If granular activated carbon is used to remove metallic impurities, then the purification process is simple, but the metallic impurity content cannot be reduced to 100 ppb or less
Solution Approach 1:
The patent uses fibrous activated carbon with specific pore structure and surface properties to enhance adsorption capacity for metallic impurities. The fibrous structure provides larger surface area and improved contact efficiency compared to granular activated carbon, enabling reduction of metallic impurities to 100 ppb or less while maintaining process simplicity.
Solution Approach 2:
The patent changes the physical form parameter of activated carbon from granular to fibrous, and optimizes surface area and pore volume parameters to achieve superior purification performance. This parameter change enables the system to meet the stringent requirement of 100 ppb or less metallic impurity content.
2Manufacturing precision
If coconut shell activated carbon is used, then nickel content can be reduced to about 100 ppb, but the carbon becomes fine powder causing clogging and dust scattering
Solution Approach 1:
The patent employs fibrous activated carbon with controlled pore structure that maintains mechanical integrity while providing high adsorption capacity. The fibrous form prevents disintegration into fine powder, eliminating clogging and dust scattering issues associated with granular coconut shell activated carbon, while achieving nickel content reduction to 100 ppb or less.
Solution Approach 2:
The patent uses fibrous activated carbon as a composite material structure that combines the adsorption effectiveness of coconut shell carbon with the mechanical stability of fibrous form. This composite approach resolves the contradiction between achieving low nickel content and maintaining operational ease.
3Manufacturing precision
If activated carbon is used to remove copper, then copper removal is achieved, but no effective method was previously known
Solution Approach 1:
The patent demonstrates that fibrous activated carbon with optimized pore structure and surface area can effectively adsorb copper ions from aqueous alkaline solutions. This resolves the previous technical gap where no effective copper removal method using activated carbon was known, enabling comprehensive removal of multiple metallic impurities including copper to 100 ppb or less.
4Manufacturing precision
If electrolysis with cation-exchange membrane is used, then metallic impurity content can be reduced to 10 ppb or less, but the process is low in efficiency due to simultaneous concentration increase
Solution Approach 1:
The patent extracts metallic impurities from aqueous alkaline solutions through adsorption on fibrous activated carbon, separating the purification function from concentration adjustment. This differs from electrolysis which simultaneously performs both functions inefficiently. The adsorption method achieves 10 ppb or less metallic impurity content while maintaining high productivity and process efficiency.
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 effectively reduces metallic impurities to levels below 10 ppb, making the aqueous alkaline solutions suitable for use as etching agents, improving the electrical properties of silicon wafers and enabling industrial-scale production of high-purity solutions.
Implementation Method 1
bringing a fibrous activated carbon into contact with an aqueous alkaline solution to remove a metal component other than alkali metals and alkaline earth metals from the aqueous alkaline solution
Data Source
AI summary
A method for purifying an aqueous alkaline solution, which comprises: bringing a fibrous activated carbon into contact with an aqueous alkaline solution to remove a metal component other than alkali metals and alkaline earth metals from the aqueous alkaline solution.