Backside Image Sensor Trench Layout for Reduced Pad Step Height
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Solution Overview
Problem
Existing image sensors face challenges in reducing the step difference between the pixel array region and the pad area, which affects image quality and yield.
Innovation Solution
The image sensor design includes a substrate with a pixel array region, a light-blocking region, and a pad region, featuring a back surface trench with a conductive pad and vias that extend from the second surface towards the first surface, allowing for improved electrical connectivity and reduced step differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the step difference between the pixel array region and the pad area is reduced, then image quality is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent introduces a back surface trench that extends vertically from the back surface toward the front surface of the substrate. This vertical dimension approach allows the conductive pad and via structures to be positioned at different depths, enabling step difference reduction without requiring complex lateral adjustments or additional processing layers on the front surface.
Solution Approach 2:
The patent implements a nested structure where the back surface via is positioned within the back surface trench, and the conductive pad is positioned within the back surface trench. This nesting arrangement allows multiple functional elements to be compactly integrated in the vertical dimension, reducing the horizontal step difference between regions while maintaining manufacturing feasibility.
2Manufacturing precision
If the step difference between the pixel array region and the pad area is reduced, then image quality is improved, but the manufacturing process becomes more complex
Solution Approach 1:
By utilizing the vertical dimension through the back surface trench structure, the patent achieves step difference reduction without requiring complex multi-step lateral patterning or additional front surface processing. The trench provides a vertical pathway that simplifies the manufacturing sequence compared to traditional planar approaches.
Solution Approach 2:
The patent inverts the traditional approach by implementing the conductive pad and via structures on the back surface of the substrate rather than the front surface. This inversion allows the trench and conductive elements to be formed after the pixel array is complete, enabling step difference reduction without interfering with the pixel fabrication process.
3Reliability
If back surface via structures are added to reduce step difference, then electrical connectivity is improved, but the device complexity increases
Solution Approach 1:
The back surface via is nested within the back surface trench, creating a compact vertical structure. This nesting allows the via to be positioned precisely at the required depth while maintaining a clean, integrated appearance. The trench walls provide natural sidewall support, reducing the need for additional structural reinforcement or complex alignment mechanisms.
Solution Approach 2:
The patent uses the vertical dimension of the back surface trench to achieve precise electrical connectivity control. By adjusting the depth and positioning of the via within the trench, the design can optimize electrical pathways without adding horizontal complexity or requiring additional interconnection layers.
Data Source
AI summary
An image sensor includes a substrate that includes a first surface and a second surface that faces the first surface, where the substrate includes a pixel array region, a light-blocking region that at least partially surrounds the pixel array region, and a pad region that at least partially surrounds the light-blocking region, a back surface trench that is in the pad region and extends from the second surface toward the first surface of the substrate, a back surface conductive pad in the back surface trench, and a first back surface via that is in the back surface trench and in a first hole that is spaced apart from the back surface conductive pad in a horizontal direction, where the first back surface via includes a first conductive pattern on an inner surface of the first hole and a second conductive pattern on the first conductive pattern.