Metal Indentation for Inter-Metal 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 separation by filling outer regions of wide trenches with a filler layer, which is then etched back to match the central region depth, and shaping the underlying metal layer to create depressions where necessary, thereby maintaining adequate physical separation between metal layers.
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 circuits, but the trenches become deeper in outer regions than in central regions, reducing separation between metal layers
Solution Approach 1:
Depressions are formed in the first metal layer at locations where the wide trench will be subsequently formed. This preliminary action compensates for the anticipated uneven etching that will occur in the wide trench, ensuring that when metal is deposited in the trench, adequate separation from the underlying metal layer is maintained throughout the entire trench width.
Solution Approach 2:
The depressions in the first metal layer are strategically positioned only in specific locations where wide trenches will be formed and where separation is most critical. This localized modification allows the metal layer to have different depths in different regions, compensating for the uneven trench etching and maintaining consistent separation between metal layers.
2Reliability
If wide trenches are etched deeper to accommodate metal lines, then adequate metal coverage is achieved, but breakdown voltage between metal layers is reduced
Solution Approach 1:
By forming depressions in the first metal layer before creating the wide trench, the invention prepares the structure in advance to maintain adequate separation. This preliminary action ensures that when the trench is etched and metal is deposited, the breakdown voltage between metal layers is preserved while still achieving adequate metal line coverage.
3Object-affected harmful factors
If the dielectric layer thickness is increased to maintain separation, then breakdown voltage improves, but device height and complexity increase
Solution Approach 1:
Instead of uniformly increasing the dielectric layer thickness throughout the entire device, the invention locally modifies the first metal layer by forming depressions only in specific areas where wide trenches will be formed. This localized approach maintains adequate separation and breakdown voltage without increasing the overall device height or dielectric thickness.
Data Source
AI summary
A first depression and a second depression are formed in an upper surface of a first metal layer. A dielectric layer is formed over the first metal layer. Subsequently, a wide trench is formed in the dielectric layer, the wide trench extending deeper in a first outer region and in a second outer region than in a central region located between the first outer region and the second outer region, the first outer region overlying the first depression and the second outer region overlying the second depression.