Selective Wet Etching of Ruthenium Using Basic pH Solution
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Solution Overview
Problem
Ruthenium (Ru) metal and its oxide are resistant to removal by conventional wet etching techniques, making it difficult to etch or pattern Ru structures in semiconductor devices, and dry etching methods are complex and hazardous due to the formation of toxic ruthenium tetroxide.
Innovation Solution
A wet etching process using a chemical composition with an oxidizer, buffer agent, and pH adjusting agent is employed to selectively etch ruthenium and other metals, such as copper, without damaging dielectric materials, by controlling the pH to a basic level, allowing for the formation of a recessed structure in semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dry etching is used to remove Ru, then Ru can be etched, but toxic ruthenium tetroxide is formed and processing complexity increases
Solution Approach 1:
The patent changes the chemical parameters of the etching process by using a basic pH solution (pH > 7) containing specific oxidizers instead of traditional dry etching methods. This parameter change enables Ru etching while avoiding the formation of toxic RuO4 gas, thus resolving the contradiction between etching capability and harmful byproduct formation
Solution Approach 2:
The patent replaces the physical/mechanical dry etching process with a chemical wet etching process. This substitution allows Ru to be etched through chemical reactions in a basic solution, eliminating the need for plasma-based dry etching that produces toxic ruthenium tetroxide
2Productivity
If conventional wet etching is used, then other metals can be etched, but Ru metal and ruthenium dioxide are resistant to removal
Solution Approach 1:
The patent applies local quality by creating different etching environments for different metals. The basic pH solution with specific oxidizers provides selective etching capability: it effectively removes Ru and RuO2 while maintaining appropriate etching rates for other metals like Cu, Al, and W, thus resolving the contradiction between removing Ru and etching other metals
Solution Approach 2:
The patent changes the chemical parameters of the wet etching solution by adjusting pH to basic levels (>7) and selecting specific oxidizers. This parameter change transforms the etching solution from one that cannot remove Ru to one that selectively etches Ru while maintaining compatibility with other metal etching requirements
3Reliability
If harsh etchants are used to remove Ru, then Ru can be dissolved, but the etchants are unsuitable for semiconductor processing
Solution Approach 1:
The patent changes the parameters of the etching solution by using mild basic pH conditions (>7) rather than harsh conditions. This parameter change enables Ru dissolution through controlled chemical reactions that are compatible with semiconductor processing requirements, avoiding the need for molten alkali salts or extremely aggressive etchants
Solution Approach 2:
The patent introduces specific oxidizers as intermediaries that facilitate Ru dissolution under mild conditions. These oxidizers act as mediators that enable the dissolution of Ru and RuO2 without requiring harsh etchants, thus resolving the contradiction between Ru removal capability and processing compatibility
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 enables selective removal of Ru and Cu without damaging dielectric materials, reducing complexity and hazards associated with dry etching, and allows for precise patterning and alignment in semiconductor devices.
Implementation Method 1
A wet etching process using a chemical composition with an oxidizer, buffer agent, and pH adjusting agent is employed to selectively etch ruthenium and other metals
Implementation Method 2
by controlling the pH to a basic level, allowing for the formation of a recessed structure in semiconductor devices
Data Source
AI summary
A method for forming a conductive structure for a semiconductor device includes depositing a barrier layer in a trench formed in a dielectric material and forming an interface layer over the barrier layer. A main conductor is formed over the interface layer, and the main conductor is recessed selectively to the interface layer and the barrier layer to a position below a top surface of the dielectric layer. The interface layer is selectively wet etched to the main conductor and the barrier layer using a chemical composition having an oxidizer, wherein the chemical composition is buffered to include a pH above 7. The barrier layer is selectively etching to the main conductor and the interface layer.