Non-aqueous Electroless Copper Plating for Tantalum Nitride Adhesion
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Solution Overview
Problem
Conventional electroless copper deposition processes face challenges with alkaline pH solutions, including non-compatibility with positive photoresist, longer induction times, decreased nucleation density, and oxidation of substrate surfaces, particularly tantalum nitride, leading to adhesion issues and blotchy plating.
Innovation Solution
A non-aqueous electroless copper plating solution is developed, comprising an anhydrous copper salt, an anhydrous cobalt salt, a polyamine complexing agent, and a halide source, maintained in an acidic to weakly alkaline pH environment to enhance adhesion and nucleation density, while avoiding oxidation of substrate surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high alkaline pH is used to enhance deposition rate, then deposition rate is improved, but adhesion deteriorates and nucleation density decreases
Solution Approach 1:
The patent changes the pH parameter from high alkaline (pH>9) to acidic or neutral (pH≤7), which fundamentally alters the chemical environment. This parameter change resolves the contradiction by enabling both good adhesion and adequate nucleation density while maintaining reasonable deposition rates through optimized formulation rather than relying on high pH
2Productivity
If high alkaline pH is used to enhance deposition rate, then deposition rate is improved, but nucleation density decreases
Solution Approach 1:
The patent changes the pH parameter from high alkaline to acidic or neutral conditions, which fundamentally improves nucleation density. The acidic/neutral environment prevents hydroxylate formation that inhibits nucleation, allowing for fine-grained, high-density copper deposition while maintaining productivity through optimized reducing agent and metal salt concentrations
3Ease of manufacture
If aqueous base solution is used, then electroless deposition can be performed, but oxidation of substrate surfaces occurs
Solution Approach 1:
The patent changes the solution chemistry from aqueous base to non-aqueous acidic or neutral formulation. This parameter change eliminates the oxidation problem because the acidic/neutral environment does not promote oxidative reactions, while the non-aqueous solvent system maintains electroless deposition capability through alternative reaction mechanisms that do not require water
Solution Approach 2:
The patent creates an inert chemical environment by using non-aqueous solvents and controlling pH to acidic or neutral levels, which prevents oxidation of sensitive substrates like tantalum nitride. This inert environment allows the substrate to remain in its protective oxide-free state during deposition
4Productivity
If high alkaline pH is used, then deposition rate is enhanced, but compatibility with positive photoresist is lost
Solution Approach 1:
The patent changes the pH parameter from high alkaline to acidic or neutral, which fundamentally improves compatibility with positive photoresist. The acidic/neutral environment does not attack or degrade the photoresist, allowing standard positive resist materials to be used without special protective measures, while deposition rate is maintained through optimized formulation
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 solution improves adhesion of reduced copper on wafer surfaces, increases nucleation density, and prevents oxidation, resulting in smooth, glossy, and high ductility copper deposition with improved selectivity over barrier materials and compatibility with standard positive resist photomasks.
Implementation Method 1
a polyamine complexing agent
Implementation Method 2
During electroless copper deposition, electrons are transferred from a reducing agent to the copper ions resulting in the deposition of reduced copper onto the wafer surface
Data Source
AI summary
A non-aqueous electroless copper plating solution that includes an anhydrous copper salt component, an anhydrous cobalt salt component, a non-aqueous complexing agent, and a non-aqueous solvent is provided.