Composite Seal Structure for CMP-Uniform Semiconductor Wafers
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Solution Overview
Problem
Existing seal structures in semiconductor wafers face challenges due to increased pattern density differences between the device region and seal ring, leading to issues like chemical mechanical polish (CMP) loading and defects, as features in the device region scale down while those in the seal ring remain large to provide protection.
Innovation Solution
A composite seal structure is introduced, comprising a buffer region between the device region and the seal ring, with a pattern density gradient that reduces the difference between the device and seal ring densities, using a buffer region with segmented gate structures to mitigate these issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the seal ring features are kept large to provide mechanical protection, then the protection capability is improved, but the pattern density difference between device region and seal ring increases causing CMP loading and defects
Solution Approach 1:
The seal ring is divided into multiple segments or regions with different feature sizes. The device region maintains small features for high density, while the seal ring is segmented into areas with progressively larger features, creating a gradient that provides mechanical protection without creating excessive pattern density differences that would cause CMP loading issues
Solution Approach 2:
Different regions of the seal structure are assigned different feature densities locally. The inner seal region adjacent to the device has features closer in size to device features, while outer seal regions have progressively larger features. This local variation in quality allows each region to fulfill its specific function while maintaining overall CMP process uniformity
2Productivity
If device region features are scaled down to increase integration density, then the functional density is improved, but the pattern density difference with seal ring increases leading to CMP loading issues
Solution Approach 1:
The seal structure is segmented into multiple zones with different pattern densities. This segmentation allows the device region to achieve high integration density with scaled-down features while the seal structure contains zones with progressively lower density, preventing excessive pattern density differences that would cause CMP loading problems
Solution Approach 2:
The pattern density parameter of the seal structure is varied across different regions rather than being uniform. By changing the density parameter from the device region outward through the seal structure, the patent enables high device integration density while maintaining CMP process uniformity through controlled density transitions
3Ease of manufacture
If a simple seal ring structure is used, then the fabrication is simplified, but the pattern density difference with device region causes CMP loading and defects
Solution Approach 1:
The seal ring is segmented into multiple regions with different feature densities, creating a gradient structure. This segmentation approach maintains relative fabrication simplicity while avoiding the CMP loading and defect issues that arise from uniform dense seal rings, as the gradual density transition prevents abrupt pattern density differences
Data Source
AI summary
A semiconductor structure includes a device region and a seal structure surrounding the device region. The seal structure includes an outer ring surrounding the device region and a buffer region disposed between the outer ring and the device region. The buffer region includes a first portion having a number of first gate structures extending lengthwise along a first direction and a second portion having a number of second gate structures extending lengthwise along the first direction. The second portion of the buffer region is disposed between the first portion of the buffer region and the outer ring. Along a second direction that is substantially perpendicular to the first direction, a width of each of the first gate structures is greater than a width of each of the second gate structures.