Image Sensor Cu-to-Cu Bonding Pad Structure for Leakage Control
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Solution Overview
Problem
Current image sensors face challenges in improving electrical properties and fabrication efficiency, particularly in the design and bonding of circuit and image sensor chips, which affect the overall performance and production process.
Innovation Solution
The proposed solution involves a specific configuration of bonding pads with unique structural features, including a first bonding pad with a negative slope sidewall and a second bonding pad with a stepped structure, which are directly bonded without a via part, allowing for a Cu-to-Cu bonding structure that prevents hillock formation and leakage current, thereby simplifying the fabrication process and enhancing electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bonding pad structures are used, then the fabrication process is simpler, but electrical properties deteriorate due to hillock formation and leakage current
Solution Approach 1:
The bonding pad structure employs asymmetric sidewall slopes where the first sidewall has a negative slope and the second sidewall has a positive slope. This asymmetric configuration prevents hillock formation during bonding while maintaining electrical integrity, resolving the contradiction between reliability improvement and structural complexity
Solution Approach 2:
The patent introduces a stepped structure in the second bonding pad that creates multiple horizontal levels. This dimensional change from a simple planar structure to a multi-level stepped structure prevents leakage current paths while managing the complexity through controlled geometric modification
2Reliability
If multiple interlayer dielectric layers and via parts are used, then electrical connections are more robust, but fabrication efficiency decreases
Solution Approach 1:
The patent extracts and eliminates the via part from the bonding structure, achieving direct Cu-to-Cu bonding between bonding pads. This removal of the intermediate via structure simplifies the fabrication process and improves productivity while maintaining reliable electrical connections through direct metal-to-metal contact
Solution Approach 2:
The bonding pad structure merges the functions of multiple interlayer dielectric layers into a simplified configuration where the first and second interlayer dielectric layers are consolidated. This merging reduces the total number of layers and processing steps while preserving the necessary electrical isolation and connection reliability
Data Source
AI summary
An image sensor comprising a circuit chip and an image sensor chip on the circuit chip. The image sensor chip includes a first substrate extending in a first direction and a second direction, a first interlayer dielectric layer between the first substrate and the circuit chip, and a first bonding pad in the first interlayer dielectric layer and having a first width in a first direction. The circuit chip includes a second substrate, a second interlayer dielectric layer and a third interlayer dielectric layer that are sequentially stacked on the second substrate, and a second bonding pad in the second and third interlayer dielectric layers and having a second width in the first direction. The first and second bonding pads are in contact with each other. A change in the second width along a third direction is greater than a change in the first width along the third direction, the third direction intersects the first and second directions.