Cyclic Plasma Etch for Silicon Nitride Selectivity
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Solution Overview
Problem
Current dry etch processes for silicon nitride in the semiconductor industry face challenges such as low selectivity over silicon dioxide and silicon, slow etch rates, and poor vertical loading in high aspect ratio structures, which can lead to device failure and inefficiencies in 3D NAND memory device fabrication.
Innovation Solution
A method involving a cyclic deposition and etch process using a plasma processing apparatus, where a workpiece with alternating silicon nitride and silicon dioxide layers is exposed to radicals generated from deposition and etch process gases, allowing for selective removal of silicon nitride layers at a higher rate than silicon dioxide layers, achieving improved vertical loading and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If current dry etch processes are used for silicon nitride, then etching can be performed, but selectivity over silicon dioxide and silicon is low
Solution Approach 1:
The patent segments the etching process into multiple distinct steps with different gas chemistries. First, a breakthrough etch step uses CF4/O2 plasma to penetrate and remove oxide layers. Then, a main etch step uses CF4/H2 plasma to selectively etch silicon nitride at high rates while protecting silicon dioxide. This segmentation allows each step to be optimized for its specific function, achieving both high selectivity and complete removal of sacrificial layers.
Solution Approach 2:
The patent changes process parameters between etching steps, specifically gas composition and power levels. The breakthrough step uses oxygen-rich plasma (CF4/O2) to enable oxide removal, while the main selective etch step uses hydrogen-rich plasma (CF4/H2) to protect oxide and enhance silicon nitride etching. Power parameters are also adjusted between steps to control etch rate and selectivity, allowing precise control over the etching process.
2Productivity
If dry etch processes are used for silicon nitride, then etching can be performed, but etch rates are slow
Solution Approach 1:
The patent divides the etching process into a fast breakthrough step and a selective main etch step. The main etch step using CF4/H2 plasma achieves high silicon nitride etch rates (greater than 100 nm/min) while maintaining selectivity. The breakthrough step, though slower, is brief and only needs to penetrate the oxide layer. This segmentation allows the process to achieve both high overall productivity and high selectivity.
Solution Approach 2:
The patent uses composite gas chemistries combining fluorocarbon (CF4) with hydrogen (H2). The fluorocarbon provides aggressive etching of silicon nitride through fluorine radical reactions, while hydrogen passivates silicon dioxide surfaces to prevent etching. This composite approach creates a synergistic effect where the combination of gases achieves both high etch rate and high selectivity, neither of which could be achieved with single gases alone.
3Manufacturing precision
If dry etch processes are used for high aspect ratio structures, then etching can be performed, but vertical loading is poor
Solution Approach 1:
The patent employs periodic alternation between breakthrough etching and main selective etching cycles. Each cycle consists of a brief breakthrough step followed by a longer main etch step. This periodic action allows reactive species to periodically refresh and penetrate deep into high aspect ratio structures, improving vertical loading. The cyclic nature ensures that etching proceeds uniformly from top to bottom of the high aspect ratio features while maintaining overall process productivity.
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 achieves high silicon nitride etch rates, enhanced selectivity, and precise vertical loading control, significantly improving the processing efficiency and reducing damage to the substrate, thereby addressing the limitations of existing dry etch processes.
Implementation Method 1
A plasma processing apparatus includes a plasma generation region separated from a processing region by a separation grid assembly. The separation grid assembly is configured to filter ions from plasma generated in the plasma generation region to generate a filtered plasma mixture. The filtered plasma mixture includes a higher concentration of reactive neutral species and a lower concentration of charged species compared to unfiltered plasma.
Implementation Method 2
The separation grid assembly is configured to filter ions from plasma generated in the plasma generation region to generate a filtered plasma mixture. The separation grid assembly includes a first separation grid and a second separation grid spaced apart from each other.
Data Source
AI summary
Apparatus, systems, and methods for conducting an etch removal process on a workpiece are provided. The method can include generating a plasma from a deposition process gas in a plasma chamber using a plasma source to deposit a passivation layer on certain layers of a high aspect ratio structure. The method can include generating a plasma from an etch process gas in a plasma chamber using a plasma source to remove certain layers from the high aspect ratio structure. The method can include removing silicon nitride layers at a faster etch rate than silicon dioxide layers on the high aspect ratio structure.