Metal Line Trench Modification for Breakdown Voltage
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Solution Overview
Problem
In NAND flash memories, inadequate separation between metal layers due to uneven etching of wide trenches can lead to reduced breakdown voltage and increased coupling between layers, causing operational issues.
Innovation Solution
The solution involves modifying the etch process to ensure even trench depth by using a filler layer that fills outer regions of wide trenches and etching back to match the central region depth, and shaping the underlying metal layer with depressions to maintain adequate separation, thereby reducing the depth difference and ensuring consistent breakdown voltage across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wide trenches are etched in the dielectric layer, then metal lines can be formed to connect NAND strings, but the trenches become deeper in outer regions than in central regions, reducing separation between metal layers
Solution Approach 1:
A filler layer is deposited in the wide trench before forming the second metal layer. This preliminary action compensates for the uneven trench depth by filling the deeper outer regions, ensuring that the metal layer will have adequate separation from the first metal layer across the entire substrate area.
Solution Approach 2:
The filler layer acts as an intermediary material between the first and second metal layers. It is selectively deposited in the wide trench to compensate for depth variations, thereby mediating the separation distance between the two metal layers and ensuring consistent breakdown voltage.
2Reliability
If wide trenches are etched to connect metal lines, then electrical connectivity is achieved, but inadequate separation between metal layers results, reducing breakdown voltage
Solution Approach 1:
The filler layer is selectively deposited only in the wide trench regions where inadequate separation occurs, rather than uniformly across the entire substrate. This local quality approach addresses the specific problem area while maintaining the electrical connectivity function of the wide trenches.
Solution Approach 2:
The filler layer is deposited in advance, before the second metal layer is formed. This preliminary action ensures that the separation issue is addressed before the metal layer is created, preventing harmful coupling between layers while maintaining necessary electrical connectivity.
3Productivity
If the trench depth varies between outer and central regions, then etching is simpler, but the breakdown voltage becomes inconsistent across the substrate
Solution Approach 1:
The filler layer changes the physical parameters of the trench region by filling the deeper outer areas. This parameter change compensates for the etching depth variations, ensuring that the final separation distance between metal layers is consistent across the substrate, thereby maintaining uniform breakdown voltage.
Solution Approach 2:
The filler layer is deposited preliminarily to compensate for etching depth variations. This preliminary action allows the etching process to remain simple and efficient while still achieving consistent breakdown voltage through the subsequent filler deposition that levels the trench bottom.
Data Source
AI summary
A wide trench having a width W1 and narrow trenches having a width W2 that is less than W1 are formed in a dielectric layer, the wide trench extending deeper in outer regions than in a central region. A trench modification step changes the width of the wide trench and reduces a depth difference between the outer regions and the central region of the wide trench.