Vertical NAND Source Line Layout to Prevent Pillar Disconnect
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Solution Overview
Problem
Existing manufacturing methods for vertical NAND flash memory face challenges such as high source line resistance and dopant diffusion issues, particularly when forming diffused source lines parallel to word lines, which can lead to source line bounce and disconnect the cell pillar body from the substrate.
Innovation Solution
A method is developed where diffused source lines are formed first, followed by cell stacking layers and cell pillars are aligned to these source lines, ensuring they run perpendicular to word lines and are electrically connected to the ion-implanted well, thus reducing resistance and preventing dopant diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffused source lines are formed parallel to word lines in existing manufacturing methods, then the manufacturing process is simplified, but source line resistance increases and dopant diffusion issues occur
Solution Approach 1:
The patent inverts the conventional approach by forming source lines perpendicular to word lines instead of parallel, and by forming cell pillars after source lines rather than before. This inversion resolves the technical contradiction by eliminating dopant diffusion issues and source line bounce while maintaining manufacturing feasibility through the use of alignment marks for precise positioning.
2Manufacturing precision
If cell pillars are formed before source lines in existing methods, then alignment is easier, but source line bounce occurs and electrical connectivity is lost
Solution Approach 1:
The patent applies preliminary action by forming source lines first with proper doping before forming cell pillars. This sequence ensures that the source lines are already in place and properly doped, preventing source line bounce and maintaining electrical connectivity. Alignment marks are used to ensure precise positioning of pillars relative to the pre-formed source lines.
3Ease of manufacture
If source lines are formed with conventional doping methods, then manufacturing is straightforward, but high resistance and dopant diffusion occur
Solution Approach 1:
The patent changes the parameter of source line orientation from parallel to perpendicular relative to word lines. This parameter change fundamentally alters the doping behavior, preventing dopant diffusion into adjacent structures while maintaining straightforward manufacturing processes. The perpendicular orientation combined with alignment marks achieves precise dopant placement control.
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 reduces source line resistance and maintains electrical connectivity between the cell pillars and the substrate, enhancing the reliability and efficiency of vertical NAND flash memory devices.
Implementation Method 1
forming source lines in a cell area of a substrate having an ion-implanted well
Data Source
AI summary
Disclosed is a method of manufacturing flash memory with a vertical cell stack structure. The method includes forming source lines in a cell area of a substrate having an ion-implanted well and forming an alignment mark relative to the source lines. The alignment mark is formed in the substrate outside the cell area of the substrate. After formation of the source lines, cell stacking layers are formed. After forming the cell stacking layers, cell pillars in the cell stacking layers are formed at locations relative to the previously formed source lines using the alignment mark to correctly locate the cell pillars.