SiN Spacer ALE Profile Control With Cyclic Polymer Removal
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Solution Overview
Problem
Conventional etching processes for silicon nitride (SiN) spacers in semiconductor fabrication face challenges in achieving perfect anisotropy, profile control, and minimizing damage to underlying layers, particularly at advanced technology nodes below 14 nm, where increased aspect ratios and critical dimension loss become significant issues.
Innovation Solution
A cyclic atomic layer etching (ALE) method using hydrofluorocarbon (HFC) gases with specific formulas (CxHyFz, where x=2-5, y>z) is employed, alternating between depositing a polymer layer on the SiN surface and removing it with an inert gas plasma, repeated until the SiN layer is fully etched, forming vertically straight spacers with high selectivity and minimal footing and fluorine residue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching using fluorocarbon-based chemistry is used for SiN spacer etching, then etching capability is achieved, but profile control deteriorates with increased aspect ratios at advanced technology nodes
Solution Approach 1:
The etching process is segmented into multiple alternating steps: a fluorocarbon-based plasma etching step followed by a nitrogen plasma passivation step. This segmentation allows the etching to proceed in controlled increments, with each cycle removing a thin layer of SiN while preserving sidewall profile control, thereby resolving the contradiction between etching capability and profile control in high aspect ratio structures.
Solution Approach 2:
The patent implements periodic action through cyclic repetition of the etching-passivation sequence. Multiple cycles of fluorocarbon etching followed by nitrogen passivation are performed, allowing progressive removal of SiN material while maintaining consistent profile control throughout the etch depth, thus addressing the profile control deterioration that occurs with increased aspect ratios in conventional continuous etching.
2Manufacturing precision
If fluorocarbon-based plasma etching is used to etch SiN spacers, then anisotropic etching is achieved, but damage to underlying layers increases
Solution Approach 1:
The nitrogen plasma passivation step is applied preliminarily after each fluorocarbon etching cycle to protect the freshly exposed SiN surface and underlying layers. This preliminary protective action prevents excessive ion bombardment damage and chemical contamination that would otherwise occur during subsequent etching steps, thereby maintaining anisotropic etching capability while reducing damage to underlying layers.
Solution Approach 2:
The cyclic etching-passivation process provides beforehand cushioning by repeatedly applying nitrogen plasma protection before the next fluorocarbon etching attack. This cushioning effect accumulates through multiple cycles, progressively removing SiN material while the repeated passivation steps continuously shield the underlying layers from damage, thus resolving the contradiction between achieving anisotropic etching and minimizing substrate damage.
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 profile control, reduces footing by over 70%, maintains chemical integrity, and achieves a smooth surface with minimal fluorine residuals, improving the fidelity and quality of SiN spacers in semiconductor applications.
Implementation Method 1
exposing a SiN layer covering structures on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer
Implementation Method 2
exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on etch front
Data Source
AI summary
Cyclic etch methods comprise the steps of: i) exposing a SiN layer covering a structure on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer, the HFC having a formula CxHyFz where x=2-5, y>z, the HFC being a saturated or unsaturated, linear or cyclic HFC; ii) exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on an etch front; and iii) repeating the steps of i) and ii) until the SiN layer on the etch front is selectively removed, thereby forming a substantially vertically straight SiN spacer comprising the SiN layer on the sidewall of the structure.