Composite Hard Mask Via Etching for Deep 3D Memory Openings
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Solution Overview
Problem
Existing methods for forming three-dimensional memory devices struggle with efficiently creating deep via openings, which is crucial for the formation of vertical NAND strings and other advanced memory structures.
Innovation Solution
The method involves forming an alternating stack of material layers, applying a hard mask layer, patterning a photoresist layer, and performing anisotropic etch processes to transfer cavity patterns through the stack, utilizing a combination of a cladding liner and the hard mask layer as an etch mask to extend via openings through the source-level semiconductor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-layer hard mask methods are used for via formation, then the process is simple, but the precision and depth control of deep via openings deteriorate
Solution Approach 1:
The hard mask structure is segmented into multiple layers (first hard mask layer and second hard mask layer) with different etch selectivities. The first hard mask layer has higher etch selectivity than the second hard mask layer, allowing precise control of via openings at different depths through selective etching processes.
Solution Approach 2:
Different regions of the mask structure have different etch selectivity properties. The first hard mask layer is designed with higher etch selectivity to protect underlying structures during initial etching, while the second hard mask layer has lower etch selectivity for subsequent etching stages, enabling localized precision control at different via depths.
2Productivity
If deep via openings are formed through alternating stacks, then vertical NAND strings can be constructed, but the etching process becomes complex and time-consuming
Solution Approach 1:
The alternating stack of material layers and sacrificial layers is prepared in advance before via etching. The sacrificial layers are positioned at specific depths to be removed during etching, creating the desired via pattern without requiring complex real-time process control.
Solution Approach 2:
The etching process utilizes changes in etch selectivity parameters between different material layers. By controlling the etch selectivity ratios between the hard mask layers and the alternating stack materials, the process achieves precise via formation through multiple etching steps with varying conditions.
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 enables the precise formation of deep via openings, facilitating the construction of complex three-dimensional memory structures with improved efficiency and accuracy.
Implementation Method 1
forming via openings through the alternating stack by performing an anisotropic etch process that transfers a pattern of the cavities in the hard mask layer through the alternating stack
Implementation Method 2
forming a cladding liner on sidewalls of the cavities in the hard mask layer and on a top surface of the hard mask layer
Data Source
AI summary
A source-level semiconductor layer and an alternating stack of first material layers and second material layers is formed above a substrate. A hard mask layer is formed over the alternating stack, and is subsequently patterned to provide a pattern of cavities therethrough. Via openings are formed through the alternating stack by performing an anisotropic etch process. A cladding liner is formed on sidewalls of the cavities in the hard mask layer and on a top surface of the hard mask layer. The via openings are vertically extended at least through the source-level semiconductor layer by performing a second anisotropic etch process employing a combination of the cladding liner and the hard mask layer as an etch mask.