Split Channel NAND Structure for Multi-Site Cell Separation
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Solution Overview
Problem
The challenge in semiconductor memory devices is to increase cell density while maintaining reliable performance and operational efficiency, particularly in NAND flash memory, where high string current and carrier mobility are crucial for differentiating ON and OFF cells, and process innovation is needed to achieve this without increasing manufacturing costs.
Innovation Solution
A method is employed to form a split storage structure by alternately stacking oxide and nitride layers, etching asymmetric holes, and using TEOS gap-fill to create recessed pockets for channel separation, ensuring sufficient storage area and avoiding oxidation-induced dimensional changes, allowing for multi-site cell configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cell density is increased by shrinking device dimensions, then storage capacity per unit space improves, but string current and carrier mobility deteriorate
Solution Approach 1:
The channel layer is divided into multiple segments along the string direction using separation layers, creating multiple independent channel regions. This segmentation allows each segment to maintain sufficient length for carrier transport while achieving higher overall cell density through vertical stacking and lateral multiplication.
Solution Approach 2:
The invention transitions from two-dimensional planar scaling to three-dimensional vertical stacking by introducing separation layers that enable multi-layer channel structures. This dimensional change allows cell density to increase vertically while maintaining horizontal channel dimensions necessary for adequate string current.
2Quantity of substance
If channel layer is divided to increase cell density, then storage capacity improves, but charge storage area and cell integrity deteriorate
Solution Approach 1:
Separation layers are formed before the channel layer deposition, pre-defining the channel segmentation boundaries. This preliminary action ensures that charge storage areas are properly configured from the outset, maintaining manufacturing precision while enabling channel division for increased cell density.
Solution Approach 2:
Different regions of the structure are assigned different functions: separation layers provide electrical isolation, channel layers provide carrier transport, and charge trap layers provide storage. This local quality differentiation allows each component to be optimized independently, maintaining charge storage area integrity while enabling channel segmentation.
3Shape
If oxidation process is used to divide channel layer, then channel separation is achieved, but dimensional changes and operational reliability deteriorate
Solution Approach 1:
Separation layers made of materials such as silicon oxide or silicon nitride are introduced as intermediaries between adjacent channel regions. These intermediary layers provide electrical isolation and physical separation without requiring oxidation-induced dimensional changes, thereby maintaining manufacturing precision while achieving channel segmentation.
Solution Approach 2:
The invention changes the material parameter of the separation structure from oxidized channel regions to deposited dielectric layers. This parameter change allows precise control of separation layer thickness and properties through deposition processes, avoiding the dimensional instability associated with oxidation while achieving the desired channel separation.
Data Source
AI summary
A method for forming a split storage structure and an associated semiconductor memory device. The method forms oxide layers and nitride layers alternately stacked on a substrate, etches a hole through the oxide layers and the nitride layers, the hole having shorter axis sides and longer axis sides, etches the nitride layers to form recessed pockets between the oxide layers adjacent the longer axis sides, forms blocking layers and storage layers to fill the recessed pockets, forms a tunnel layer and a channel layer to cover walls of the storage layers inside the hole; provides an incomplete gap-filling layer in the hole, removes a part of the channel layer which is not covered by the gap-filling layer to form a split channel layer; completely removes the nitride layers to form recesses between the oxide layers; and forms conductive layers in the recesses where the nitride layers were completely removed.