Zeolite Ion Exchange for NF3 Purification
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Solution Overview
Problem
Current methods for refining nitrogen trifluoride (NF3) gas are inadequate in removing carbon tetrafluoride (CF4) due to similarities in boiling point, molecular size, and heat of adsorption, leading to impurities that cause issues in semiconductor etching.
Innovation Solution
Ion-exchanged and impregnated zeolite 3A, 4A, or 5A with alkali earth metal is used to selectively adsorb NF3, adjusting pore size through ion exchange and impregnation to differentiate between NF3 and CF4, allowing for their separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If general methods such as distillation or bulk adsorption are used to remove CF4 from NF3, then the purification process is simple, but CF4 cannot be effectively removed due to similarities in boiling point, molecular size, and heat of adsorption
Solution Approach 1:
The patent employs zeolite with specific pore size (0.3-0.5 nm) as an adsorbent to selectively adsorb NF3 molecules while excluding CF4 molecules. The porous structure of zeolite enables molecular-level separation based on size differences, achieving effective CF4 removal without requiring complex distillation equipment or multiple adsorption stages.
Solution Approach 2:
The patent modifies the local quality of the adsorbent by introducing water molecules into specific locations within the zeolite pores. This creates a selective environment where NF3 molecules can interact with water-filled pores while CF4 molecules are excluded, enabling selective adsorption without changing the overall zeolite structure or requiring complex processing equipment.
2Quantity of substance
If zeolite 5A with large pore size is used to adsorb NF3, then adsorption capacity is high, but CF4 cannot be excluded because the pore size is large enough to adsorb both NF3 and CF4
Solution Approach 1:
The patent introduces water molecules into specific locations within the zeolite pores to create a selective environment. The water molecules occupy specific sites and create steric hindrance that allows NF3 molecules to pass through and adsorb while blocking CF4 molecules, thus maintaining high adsorption capacity for NF3 while achieving selectivity against CF4.
Solution Approach 2:
The patent changes the effective pore size parameter of zeolite 5A from its original large pore size (0.5 nm) to a controlled range (0.3-0.5 nm) by controlling water content (1-10% by weight). This parameter adjustment enables the pores to be large enough to maintain high NF3 adsorption capacity but small enough to exclude CF4 molecules through steric hindrance.
3Manufacturing precision
If zeolite with small pore size (zeolite 3A or 4A) is used, then selectivity against CF4 is high, but adsorption capacity for NF3 is insufficient
Solution Approach 1:
The patent merges the advantages of different zeolite types by using zeolite 5A (which has large pore size and high adsorption capacity) combined with controlled water content (which provides selectivity). This combination achieves both high NF3 adsorption capacity and effective CF4 exclusion, overcoming the limitations of using small-pore zeolites alone.
4Manufacturing precision
If synthetic zeolite with controlled water content is used as disclosed in U.S. Pat. No. 5,069,887, then CF4 removal is effective, but the water content must be precisely adjusted and the adsorption temperature range is very narrow
Solution Approach 1:
The patent optimizes the water content parameter to a specific range (1-10% by weight) that provides both CF4 exclusion and NF3 adsorption capability. This parameter optimization broadens the operational window compared to previous patents, allowing effective purification under more varied temperature and pressure conditions without requiring precise control.
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 process effectively produces high-purity NF3 by selectively removing CF4, meeting the requirements of the semiconductor industry with improved purity and reduced impurity levels.
Implementation Method 1
zeolite 3A, 4A or 5A ion-exchanged and impregnated with alkali earth metal can be effective as a molecular sieve for selectively adsorbing NF3 from a mixture of NF3 and CF4
Implementation Method 2
zeolite 3A, 4A or 5A ion-exchanged and impregnated with alkali earth metal can be effective as a molecular sieve for selectively adsorbing NF3
Data Source
AI summary
Disclosed herein are a process for the refinement of nitrogen trifluoride gas and an adsorbent therefor. A nitrogen trifluoride (NF3) gas including carbon tetrafluoride (CF4) as an impurity is permeated into a bed of zeolite 3A, 4A or 5A which undergoes ion exchange and impregnation with alkali earth metal and is thermally treated at 150 to 600° C. for 0.5 to 100 hours so as to be able to selectively adsorb nitrogen trifluoride onto the bed, followed by the desorption of the nitrogen trifluoride therefrom.