High-Purity Hafnium Refining for Semiconductor Gate Films
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Solution Overview
Problem
Existing methods for manufacturing high-purity hafnium struggle to effectively reduce impurities such as Zr, Fe, Cr, Ni, Ca, Na, K, Al, Co, Cu, Ti, W, Zn, U, Th, Pb, Bi, and C, which are critical for its use as electronic materials in semiconductor applications due to contamination concerns and the difficulty in achieving high purification levels.
Innovation Solution
A method involving the use of hafnium sponge with reduced Zr content, where hafnium tetrachloride is distilled and refined, followed by electrolysis and electron beam melting to achieve high-purity hafnium with impurity levels below specific thresholds, enabling the formation of high-purity sputtering targets and thin films for electronic applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional refining methods are used to manufacture hafnium, then production cost and process simplicity are maintained, but impurity content (Zr, Fe, Cr, Ni, Ca, Na, K, Al, Co, Cu, Ti, W, Zn, U, Th, Pb, Bi, and C) remains high and cannot be reduced below significant levels
Solution Approach 1:
The refining process is divided into multiple sequential stages: initial sponge formation, first electrolytic refining, second electrolytic refining, and electron beam melting. Each stage targets specific impurity removal, with subsequent stages building upon previous purification to achieve cumulative purity improvements below 0.2 ppm for most impurities
Solution Approach 2:
Electrolytic refining uses an electrolyte medium (molten salt) as an intermediary to separate hafnium from impurities through selective electrochemical reactions. The electrolyte enables controlled deposition of pure hafnium at the cathode while impurities remain in solution or form sludge, achieving purification without direct mechanical separation
2Manufacturing precision
If multiple refining stages are implemented to reduce impurity content, then hafnium purity is improved, but manufacturing time and process complexity increase
Solution Approach 1:
The initial sponge formation stage performs preliminary impurity removal by eliminating common contaminants during the reduction process. This preliminary action reduces the impurity burden before electrolytic refining, allowing subsequent stages to focus on trace impurity removal and reducing overall process time
Solution Approach 2:
The process utilizes parameter changes including temperature control during electron beam melting, voltage and current density adjustments during electrolytic refining, and atmospheric control to optimize each stage's efficiency. These parameter optimizations reduce processing time while maintaining high purification effectiveness
3Ease of manufacture
If hafnium with high impurity content is used for electronic applications, then manufacturing cost is reduced, but contamination of silicon substrate and device performance degradation occur
Solution Approach 1:
The process selectively extracts harmful impurities (Fe, Cr, Ni, Ca, Na, K, Al, Co, Cu, Ti, W, Zn, U, Th, Pb, Bi, and C) from hafnium through multiple refining stages. Each extraction stage targets specific impurity groups, removing them to below 0.2 ppm levels to prevent substrate contamination while maintaining cost-effective production
Solution Approach 2:
The electron beam melting and subsequent processing are conducted in inert or vacuum atmospheres to prevent re-contamination of the purified hafnium. This inert environment protection ensures that the high-purity hafnium remains contamination-free throughout final processing and deposition onto silicon substrates
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 high-purity hafnium with impurity levels below 0.2 ppm for certain elements and 1 ppb for others, ensuring stable electronic performance and reduced contamination risks, suitable for forming gate insulation and metal gate films without disrupting silicon substrate functions.
Implementation Method 1
hafnium tetrachloride is distilled and refined
Implementation Method 2
followed by electrolysis
Implementation Method 3
electron beam melting
Data Source
AI summary
Provided is a method of manufacturing high-purity hafnium by using a hafnium sponge with reduced zirconium as the raw material in which the impurity content of Fe, Cr, and Ni, the impurity content of Ca, Na, and K, the impurity content of Al, Co, Cu, Ti, W, and Zn, the alpha dose, the impurity content of U and Th, the impurity content of Pb and Bi, and the content of C as a gas component contained in the hafnium are reduced. Based on this efficient and stable manufacturing technology, additionally provided are a high-purity hafnium material obtained from the foregoing high-purity hafnium, as well as a sputtering target, a gate insulation film and a metal gate thin film, which are formed from this material. This high-purity hafnium has a purity 6N or higher except Zr and gas components, wherein Fe, Cr and Ni are respectively 0.2 ppm or less, Ca, Na and K are respectively 0.1 ppm or less, and Al, Co, Cu, Ti, W and Zn are respectively 0.1 ppm or less.