Layer-by-Layer Etching for Mixed-CD High-Aspect-Ratio Features
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Solution Overview
Problem
Current semiconductor fabrication methods for 3D NAND devices use non-selective etch processes, which are unable to simultaneously etch features of varying critical dimensions (CDs) and high aspect ratios (HARs) without over etching underlayers, leading to poor product yield and increased manufacturing costs.
Innovation Solution
A cyclic selective etching process is employed, which involves alternating between two selective etch steps within each cycle. This process etches through a layer stack comprising alternating silicon oxide and silicon nitride layers, allowing for the simultaneous formation of features with different CDs and HARs by controlling the etch front and optimizing etch times based on the feature with the slowest etch rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-selective etch processes are used to etch through the layer stack, then the etching process is simple and fast, but over etching of underlayers occurs leading to poor product yield
Solution Approach 1:
The etching process is segmented into multiple discrete steps, each targeting a specific layer (oxide or nitride). The patterned hard mask layer contains different patterns for different features, and each etching step selectively removes one material type while preserving the other, preventing over etching of underlayers while maintaining high productivity
Solution Approach 2:
The etching process uses periodic alternation between oxide-selective etching and nitride-selective etching steps. This periodic action allows the etch front to progress through alternating layers systematically, enabling simultaneous formation of features with different CDs and HARs while controlling etch selectivity to prevent underlayer damage
2Manufacturing precision
If multiple discrete etch steps are used to etch features of different CDs and HARs, then etch selectivity is improved, but the total etch time increases
Solution Approach 1:
Multiple etching operations are merged into a single integrated process. The patterned hard mask layer with multiple patterns allows simultaneous etching of features with different CDs and HARs in one process sequence, rather than requiring separate etch steps for each feature type, thus reducing total etch time while maintaining selectivity
Solution Approach 2:
The hard mask layer is preliminarily patterned with multiple patterns before the etching process begins. This preliminary patterning allows the etch front to be controlled from the start, enabling simultaneous formation of different features in a single etch cycle sequence, reducing the need for multiple sequential etching operations
3Manufacturing precision
If the etch process is optimized for features with slow etch rate, then manufacturing precision is improved, but the total etch time increases
Solution Approach 1:
Different etching conditions and parameters are applied locally to different features based on their specific requirements. Features with slow etch rates receive optimized etching parameters during their specific etching step, while other features continue to be processed appropriately, allowing precision optimization without proportionally increasing total etch time for all features
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 cyclic etching process effectively reduces over etching of underlayers, enables simultaneous etching of features with different CDs and HARs, and decreases the total etch time, thereby improving product yield and reducing manufacturing costs.
Implementation Method 1
performing a second cyclic process to etch through the 2n alternating oxide and nitride layers of the layer stack and expose the underlayer, each cycle of the second cyclic process including a first etch step to selectively etch the oxide layer and a second etch step to selectively etch the nitride layer
Data Source
AI summary
A method of forming a device, the method includes loading a substrate into an etch chamber, the substrate including an underlayer and a pair of a first layer and a second layer, the pair being stacked to form a layer stack. The method further includes forming a patterned hard mask layer over the layer stack, the patterned hard mask layer including a pattern for forming a first set of features and a second set of features. And the method further includes performing a cyclic etching process to etch through the layer stack, each cycle of the cyclic etching process including a first etch step to selectively etch the first layer and a second etch step to selectively etch the second layer, and where the cyclic etching process forms the first and second set of features, the first having a different etch rate than the second set of features.