Three-Layer Stacked Image Sensor for Pad Alignment and Noise Shielding
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Solution Overview
Problem
Existing image sensors with stacked structures face challenges in minimizing misalignment between through electrodes and pads, and in reducing coupling noise between adjacent pads, which affects their performance and reliability.
Innovation Solution
A three-layered stacked image sensor design is implemented, featuring an upper chip with pixels, an intermediate chip with transistors, and a lower chip with image sensor processors, where the chips are bonded using copper-copper bonding and hybrid bonding techniques, with a through electrode having an inverted trapezoidal structure to minimize misalignment and a shielding conductive layer to reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional stacked structure is used, then integration is achieved, but misalignment between through electrode and pad occurs
Solution Approach 1:
The inverted trapezoidal structure of the through electrode is formed in advance during the manufacturing process, creating a wider upper surface that anticipates and compensates for potential alignment deviations during the bonding process, thereby improving alignment precision without adding complex alignment mechanisms
Solution Approach 2:
The geometry of the through electrode is changed from a conventional cylindrical or rectangular cross-section to an inverted trapezoidal cross-section, where the upper surface area is larger than the lower surface area. This parameter change in shape allows for better alignment tolerance and precision during chip stacking
2Area of stationary object
If pads are placed close together for high integration, then area is reduced, but coupling noise between adjacent pads increases
Solution Approach 1:
A shielding conductive layer is introduced as an intermediary element between adjacent pads. This shielding layer acts as a mediator that blocks or reduces the coupling noise between closely spaced pads, allowing the pads to be placed closer together for high integration without suffering from noise interference
Solution Approach 2:
The shielding conductive layer is positioned to preemptively counteract the coupling noise before it can affect the signal integrity between adjacent pads, thereby preventing noise issues before they occur in high-density pad configurations
3Length of moving object
If through electrode cross-section is reduced for miniaturization, then size is decreased, but misalignment sensitivity increases
Solution Approach 1:
The through electrode employs an asymmetric inverted trapezoidal cross-section where the upper surface area is deliberately made larger than the lower surface area. This asymmetric design allows the electrode to maintain a compact lower profile for miniaturization while providing a larger upper surface that is less sensitive to alignment deviations during bonding
Data Source
AI summary
The inventive concepts provide a three-layered stacked image sensor in which misalignment between a through electrode and a pad is reduced and coupling noise between adjacent pads is reduced, and methods of manufacturing the same. The three-layered stacked image sensor includes an upper chip including pixels arranged in a two-dimensional array structure and a first wiring layer, each of pixels including a photodiode, a transfer gate, and a floating diffusion region, an intermediate chip including a source follower gate, a select gate, and a reset gate corresponding to each of pixels, a first silicon layer, and a second wiring layer, and a lower chip including an image sensor processor, a third wiring layer, and a second silicon layer, a cross-section of an upper portion of a through electrode extending from the second wiring layer through the first silicon layer having an inverted trapezoidal structure.