FinFET Gate Stack Protection During Neutral Radical Plasma Etching
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Solution Overview
Problem
The semiconductor industry faces challenges in preventing surface damage during the formation of FinFET devices, particularly due to weaknesses in metal gate and dielectric layers that can lead to manufacturing defects and reduced integration density.
Innovation Solution
A protective layer is deposited over the metal material and dielectric layers, which is then annealed to form an oxide layer, followed by a plasma etching process using nitrogen trifluoride and hydrogen to remove the oxide layer and a radical plasma etch with neutral radicals to remove the remaining protection layer, minimizing damage and defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional plasma etching processes are used to remove protective layers, then etching efficiency is improved, but surface damage and defects in metal gate and dielectric layers increase
Solution Approach 1:
The patent divides the etching process into multiple sequential steps: first removing the oxide layer with a plasma process, then removing the protective layer with a different plasma process. This segmentation allows each step to be optimized for its specific function, achieving both efficiency and minimal damage.
Solution Approach 2:
The patent changes plasma process parameters between steps, using different gas compositions (e.g., CF4/O2 for oxide removal, then NF3/H2 for protective layer removal) and power levels to achieve selective removal while controlling surface damage. The neutral radical plasma process uses specific parameter settings to minimize ion bombardment damage.
2Manufacturing precision
If feature sizes are reduced to increase integration density, then more components can be integrated, but manufacturing defects and surface damage increase
Solution Approach 1:
The patent applies a protective layer before critical etching steps to prevent surface damage during processing. This preliminary protective action ensures that even as features shrink, the underlying structures remain intact during manufacturing, reducing defects.
Solution Approach 2:
The protective layer acts as an intermediary between the etching plasma and the sensitive metal gate/dielectric structures. It absorbs the harmful effects of plasma exposure and ion bombardment, protecting the underlying layers during the etching process.
3Productivity
If aggressive etching processes are used to remove protective layers quickly, then productivity is improved, but metal gate and dielectric layer integrity deteriorates
Solution Approach 1:
The removal process is segmented into two distinct phases: oxide layer removal followed by protective layer removal. Each phase uses plasma parameters optimized for that specific material, allowing efficient removal without compromising the integrity of underlying sensitive layers.
Solution Approach 2:
The patent replaces aggressive mechanical/physical sputtering with chemically-selective plasma etching processes. The chemical reactions between plasma species and the protective layer materials enable removal at reasonable rates while minimizing physical damage through reduced ion bombardment.
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 enhances the integrity of the metal gate and dielectric layers, reducing defects and improving the yield by maintaining the thickness of the metal layer and enhancing breakdown voltages, while also reducing the number of defective parts and improving threshold voltage.
Implementation Method 1
performing an annealing process on the gate dielectric, wherein the annealing process oxidizes a portion of the protection layer to form an oxidized portion
Implementation Method 2
followed by a plasma etching process using nitrogen trifluoride and hydrogen to remove the oxide layer
Implementation Method 3
a radical plasma etch with neutral radicals to remove the remaining protection layer
Data Source
AI summary
A method of applying and then removing a protective layer over a portion of a gate stack is provided. The protective layer is deposited and then a plasma precursor is separated into components. Neutral radicals are then utilized in order to remove the protective layer. In some embodiments the removal also forms a protective by-product which helps to protect underlying layers from damage during the etching process.