Selective Etching of Titanium Nitride Using Fluoride and Inhibitors
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Solution Overview
Problem
The challenge in the high-k/metal gate integration scheme is the selective removal of one metal gate material relative to another, particularly titanium nitride (TiNx) and tantalum nitride (TaNx), due to their similar physical and chemical properties, which complicates the process and increases costs.
Innovation Solution
A composition and method involving a fluoride-containing removal solution with a metal nitride inhibitor, such as boric acid or HEDP, and an oxidizing agent like hydrogen peroxide, are used to selectively remove one metal gate material relative to another, ensuring a high selectivity ratio without significantly affecting other gate stack materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes are used to remove metal gate materials, then the etching process can proceed, but the selectivity between different metal nitride materials (TiNx and TaNx) is poor due to their similar physical and chemical properties
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by incorporating specific metal nitride inhibitors (such as boric acid, HEDP, or their salts) alongside fluoride and oxidizing agents. This parameter modification creates a chemical environment that differentially affects TiNx and TaNx, achieving high selectivity (e.g., etching TiNx at 80-100 nm/min while inhibiting TaNx etching to less than 2 nm/min) despite the similar physical properties of these metal nitrides.
Solution Approach 2:
The patent introduces metal nitride inhibitors as intermediary substances that mediate the etching process. These inhibitors selectively interact with TaNx to form protective complexes or surface layers, preventing the fluoride and oxidizing agents from attacking TaNx, while allowing TiNx to be etched. This intermediary mechanism enables selective removal of one metal nitride over another.
2Reliability
If multiple metal gate materials are used with different work functions, then the desired electrical performance for NMOS and PMOS transistors is achieved, but the selective removal of these materials becomes challenging and costly
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching solution to create selective reactivity. By adjusting the types and concentrations of fluoride, oxidizing agents, and metal nitride inhibitors, the process achieves differential etching rates for different metal nitride materials, enabling selective removal without requiring complex multi-step processes.
Solution Approach 2:
The patent incorporates strong oxidizing agents (such as hydrogen peroxide, ozone, or their salts) into the etching solution to accelerate the oxidation of metal nitride surfaces. This oxidation step, combined with fluoride attack and inhibitor protection, creates a synergistic effect that enhances selectivity between different metal gate materials, making the manufacturing process more feasible.
3Ease of manufacture
If the etching process is made selective to one metal gate material, then the manufacturing cost and process complexity are reduced, but the selectivity ratio must be maintained high without affecting other gate stack materials
Solution Approach 1:
The patent optimizes multiple parameters of the etching solution simultaneously: the type and concentration of fluoride (0.1-10 wt%), oxidizing agents (1-30 wt%), and metal nitride inhibitors (0.1-20 wt%). This multi-parameter optimization achieves high selectivity ratios (e.g., 50:1 or higher between TiNx and TaNx etching rates) while maintaining process simplicity and avoiding damage to other gate stack materials.
Solution Approach 2:
The patent creates a composite etching solution containing multiple chemical components working together: fluoride for base etching, oxidizing agents for surface activation and selective oxidation, and metal nitride inhibitors for selective protection. This composite chemical system achieves the desired high selectivity ratio while keeping the process simple and cost-effective.
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 effectively achieves selective etching of titanium nitride over tantalum nitride with high selectivity, maintaining the integrity of other gate stack materials, thus simplifying the process and reducing costs.
Implementation Method 1
a fluoride-containing removal solution with a metal nitride inhibitor, such as boric acid or HEDP, and an oxidizing agent like hydrogen peroxide, are used to selectively remove one metal gate material relative to another
Implementation Method 2
an oxidizing agent like hydrogen peroxide, are used to selectively remove one metal gate material
Implementation Method 3
a fluoride-containing removal solution with a metal nitride inhibitor, such as boric acid or HEDP
Data Source
AI summary
A removal composition and process for selectively removing a first metal gate material (e.g., titanium nitride) relative to a second metal gate material (e.g., tantalum nitride) from a microelectronic device having said material thereon. The removal composition can include fluoride or alternatively be substantially devoid of fluoride. The substrate preferably comprises a high-k/metal gate integration scheme.