Phosphoric Acid Purification for Semiconductor Grade
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Solution Overview
Problem
Current methods for purifying phosphoric acid to achieve electronic grade purity are inadequate for effectively removing antimony and arsenic impurities, particularly due to their amphoteric nature and low solubility, leading to unsuitable semiconductor applications.
Innovation Solution
A double filtration process using hydrogen sulphide in an oxygen-free atmosphere followed by atmospheric oxygen purging with compressed air, combined with static mixers and specific filtration stages, to precipitate and oxidize antimony and arsenic compounds, ensuring thorough removal without additional reagents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sodium sulphide solution is added to remove arsenic compounds, then conversion is high and application is easy, but sodium ions are introduced in large amounts making further processing economically unprofitable
Solution Approach 1:
The patent extracts and removes harmful sodium ions from the purification process by replacing sodium sulphide with hydrogen sulphide gas. This extraction eliminates the source of sodium ion contamination while maintaining the ability to remove arsenic and antimony impurities through sulphide precipitation.
Solution Approach 2:
The patent uses hydrogen sulphide gas as an intermediary substance that mediates the removal of arsenic and antimony without introducing harmful sodium ions. Hydrogen sulphide serves as a cleaner alternative that achieves the same purification function with beneficial by-products.
2Reliability
If thermal phosphoric acid is used, then ionic impurities are low and suspended solids are free, but antimony and arsenic contamination remains at 40-70 ppm preventing direct use in semiconductors
Solution Approach 1:
The patent applies preliminary action by treating thermal phosphoric acid with hydrogen sulphide gas before the acid can be used in semiconductor manufacturing. This preliminary purification step removes antimony and arsenic impurities through sulphide precipitation, preparing the acid for subsequent electronic grade applications.
Solution Approach 2:
The patent changes the chemical parameters of the purification process by using hydrogen sulphide gas instead of traditional reagents. This parameter change enables selective precipitation of antimony and arsenic while maintaining the high ionic purity characteristics of thermal phosphoric acid.
3Manufacturing precision
If antimony sulphide particles are removed by filtration at lower temperatures, then purity increases, but viscosity increases significantly reducing filtration rate
Solution Approach 1:
The patent applies dynamics by adjusting the temperature parameter dynamically during the filtration process. The system operates at elevated temperatures during filtration to maintain low viscosity and high filtration rates, then allows temperature to decrease naturally after filtration to enable antimony sulphide precipitation without compromising productivity.
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 method achieves phosphoric acid purity suitable for semiconductor use, with arsenic and antimony levels below 1.5 ppm and sulfur below 2 ppm, enabling further processing to electronic grade.
Implementation Method 1
the said contaminated phosphoric(V) acid is mixed with hydrogen sulphide in an oxygen-free atmosphere
Implementation Method 2
the obtained filtrate is purged using compressed air
Data Source
Figure 1
AI summary
A method of purification phosphoric(V) acid with a concentration of 73 wt% to 88 wt.% for the purpose of static crystallisation to obtain an acid of the grade suitable for semiconductor industry, wherein the said phosphoric(V) acid is purified from antimony, arsenic and sulphur compounds, the process takes place in a plug flow reactor and includes the steps wherein: first said contaminated phosphoric(V) acid is mixed with hydrogen sulphide in an oxygen-free atmosphere, wherein the molar ratio of hydrogen sulphide to the total molar quantity of antimony and arsenic is 1.25-2.0, and the overpressure of the hydrogen sulphide introduced to phosphoric(V) acid is at least 1.0 bar, then the previously obtained suspension is buffered for 2-8 h, and subsequently this suspension is filtered in a pressure plate filter with the addition of powdered activated carbon and diatomaceous earth, then the filtrate is purged using compressed air with a capacity of 0.25-0.5 m3/h of air per 1 m3 of filtered phosphoric(V) acid for a minimum of 2h, then the fresh antimony sulphide suspension is filtered using a filter with a mesh size smaller than 50 µm, especially using a filter with a polymer cartridge, and finally the filtrate obtained in this way is purged using compressed air with a capacity of 0.25-0.5 m3/h per 1 m3 of filtered phosphoric(V) acid for 4-8 h.