High-Purity Lanthanum Production via Calcium Reduction and Electron Beam Melting
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Solution Overview
Problem
The production of high-purity lanthanum is challenging due to its susceptibility to oxidation, leading to defects in sputtering targets and metal gate films, and contamination from elements like Al, Fe, Cu, and rare earth impurities, which affect the electrical properties of semiconductor devices.
Innovation Solution
A method involving the reduction of lanthanum fluoride using distilled calcium followed by electron beam melting to produce high-purity lanthanum with controlled impurity levels, resulting in a sputtering target with a purity of 4N or more, excluding rare earth elements and gas components, to form high-purity metal gate films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lanthanum is purified through conventional refining processes, then some purity is achieved, but oxidation occurs during the process making high-purity product unattainable
Solution Approach 1:
The patent employs an inert atmosphere environment during the purification process to prevent oxidation of lanthanum. The reduction reaction and subsequent handling are conducted in conditions that exclude oxygen, allowing high-purity lanthanum to be obtained without oxidation interference.
Solution Approach 2:
The patent uses calcium as an intermediary reducing agent to convert lanthanum fluoride to metallic lanthanum. This intermediary approach allows purification through chemical reduction while maintaining control over the oxidation state, enabling high-purity product formation.
2Ease of operation
If lanthanum target is exposed to air for storage or handling, then ease of operation is improved, but rapid oxidation occurs within 10 minutes reducing electric conductivity and causing sputtering defects
Solution Approach 1:
The patent maintains lanthanum in an inert atmosphere environment from production through storage and handling. This continuous inert environment protection allows the material to be handled without rapid oxidation, preserving electric conductivity and preventing sputtering defects while maintaining operational ease.
Solution Approach 2:
The patent establishes inert atmosphere protection in advance before any handling or storage operations. By pre-configuring the protective environment, the lanthanum is protected from oxidation before exposure risks arise, ensuring both ease of operation and reliability are maintained.
3Adaptability or versatility
If lanthanum target is left exposed to air for long period, then handling flexibility increases, but reaction with moisture forms white hydroxide powder making sputtering impossible
Solution Approach 1:
The patent implements continuous inert atmosphere protection throughout the manufacturing and handling process. This prevents moisture reaction that would form hydroxide powder, maintaining sputtering processability while providing the handling flexibility needed for manufacturing operations.
Solution Approach 2:
The patent establishes inert atmosphere protection before any handling operations begin. This preliminary protective measure prevents moisture exposure and hydroxide formation, ensuring the lanthanum remains suitable for sputtering while allowing flexible handling during the protected period.
4Productivity
If conventional reduction method with calcium is used, then lanthanum can be produced, but slag separating jig is required and purification is incomplete
Solution Approach 1:
The patent replaces the mechanical slag separating jig with a chemical purification approach. By using controlled reduction reactions and inert atmosphere processing, the method achieves both high productivity and high purity without requiring complex mechanical separation equipment.
Solution Approach 2:
The patent optimizes the reduction process parameters, including temperature control and calcium-to-lanthanum-fluoride ratio, to maximize purity while maintaining productivity. By adjusting these parameters, complete purification is achieved without requiring additional mechanical separation steps.
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 approach stabilizes the production of high-purity lanthanum sputtering targets and metal gate films, reducing oxidation and contamination issues, thereby enhancing the performance and reliability of semiconductor devices.
Implementation Method 1
A method involving the reduction of lanthanum fluoride using distilled calcium
Implementation Method 2
electron beam melting to produce high-purity lanthanum
Data Source
AI summary
A method for producing high-purity lanthanum having a purity of 4N or more excluding rare earth elements other than lanthanum and gas components, wherein lanthanum having a purity of 4N or more is produced by reducing, with distilled calcium, a lanthanum fluoride starting material that has a purity of 4N or more excluding rare earth elements other than lanthanum and gas components, and the obtained lanthanum is subjected to electron beam melting to remove volatile substances. The method for producing high-purity lanthanum, in which Al, Fe, and Cu are respectively contained in the amount of 10 wtppm or less. The method for producing high-purity lanthanum, in which total content of gas components is 1000 wtppm or less. The present invention aims to provide a technique capable of efficiently and stably providing high-purity lanthanum, a sputtering target composed of high-purity lanthanum, and a thin film for metal gate that contains high-purity lanthanum as a main component.