Silicon Nitride Spacer Etch Selectivity via Cyclical Oxidation
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Solution Overview
Problem
The fabrication of semiconductor devices, particularly non-planar transistors, faces challenges in selectively removing spacer materials without damaging the underlying structures due to the differing heights and anisotropic etching processes, leading to increased fringe capacitance and potential electrical performance issues.
Innovation Solution
A cyclical etching and oxidation process is employed using a plasma processing system with varying gas flow ratios of halogen-containing and oxygen-containing gases to improve selectivity between silicon nitride and silicon, forming a thicker oxide protection film on silicon surfaces, allowing for more precise removal of silicon nitride spacer materials without etching the fin structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single etching process is used to remove spacer material from structures of different heights, then the etching process is simple, but the underlying material gets damaged or etched due to excessive over-etch time
Solution Approach 1:
The single etching process is divided into multiple etching steps with different gas compositions. The first etching step uses a gas mixture optimized for removing spacer material from lower structures, while the second etching step uses a different gas mixture for removing remaining spacer material from higher structures. This segmentation allows each step to be optimized for its specific task, preventing damage to underlying material while maintaining process simplicity.
Solution Approach 2:
The etching process dynamically adjusts gas composition between steps. The first etching step uses a gas mixture with parameters optimized for one etching rate, and the second etching step transitions to a different gas mixture with parameters optimized for a different etching rate. This dynamic adjustment allows the process to adapt to the varying heights of structures being etched, preventing over-etch damage while maintaining simplicity.
2Manufacturing precision
If etching time is extended to clear spacer material from fin sidewalls, then complete spacer removal is achieved, but fin structures are damaged or etched
Solution Approach 1:
The spacer removal process is segmented into two distinct etching steps. The first etching step removes spacer material from horizontal surfaces and lower fin sidewalls using a gas mixture optimized for this task. The second etching step removes remaining spacer material from higher fin sidewalls using a different gas mixture. This segmentation achieves complete spacer removal without requiring excessive total etching time that would damage fin structures.
Solution Approach 2:
The etching process changes parameters between steps, specifically the gas composition. The first etching step uses a gas mixture with parameters optimized for removing spacer from certain surfaces, while the second etching step uses a different gas mixture with parameters optimized for removing spacer from fin sidewalls. This parameter change allows precise control over etching selectivity, achieving complete spacer removal while protecting fin structures from damage.
3Manufacturing precision
If anisotropic etching is used to maintain vertical spacer material, then spacer coverage is improved, but horizontal surfaces are etched through faster requiring longer over-etch time
Solution Approach 1:
The etching process is segmented into two steps with different gas compositions. The first etching step uses a gas mixture that provides moderate anisotropy, removing spacer from horizontal surfaces and lower areas. The second etching step uses a different gas mixture with different etching characteristics to remove remaining spacer from vertical surfaces. This segmentation achieves the needed spacer coverage without requiring excessive over-etch time that would damage underlying materials.
Solution Approach 2:
The process changes gas composition parameters between etching steps. The first etching step uses a gas mixture with parameters that provide certain anisotropy levels and etching rates. The second etching step transitions to a different gas mixture with parameters optimized for removing spacer from vertical fin sidewalls. This parameter change allows the process to achieve adequate spacer coverage while minimizing the total over-etch time required, preventing damage to underlying materials.
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 method enhances etch selectivity, reduces the risk of damaging silicon surfaces, and achieves better removal of silicon nitride spacer materials, thereby improving the electrical performance of non-planar transistors by maintaining the integrity of fin structures during the fabrication process.
Implementation Method 1
a first process gas mixture is flowed into the plasma processing system... A second process gas mixture is flowed into the plasma processing system... Plasma is created and maintained using the first process gas mixture and the second process gas mixture
Implementation Method 2
The second process gas mixture includes an oxygen-containing gas... An oxidizing step creates an oxide protection film on silicon surfaces
Data Source
AI summary
Techniques herein include methods to increase etching selectivity among materials. Techniques herein include a cyclical process of etching and oxidation of a silicon nitride (SiN) spacer and silicon (such as polycrystalline silicon). This technique can increase selectivity to the silicon so that silicon is less likely to be etched or damaged while silicon nitride is etched from sidewalls. Techniques and chemistries as disclosed herein can be more selective to silicon oxide and silicon as compared to silicon nitride. An oxidizing step creates an oxide protection film on silicon surfaces that is comparatively thicker to any oxide film formed on nitride surfaces. As such, techniques here enable better removal of silicon nitride and silicon nitride spacer materials.