Pixel Isolation Structure for Void-Free Image Sensor Trenches
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Solution Overview
Problem
Current image sensors face challenges in achieving sharp images and high yield during manufacturing, particularly due to issues with pixel isolation and conductive pattern formation, which affect image resolution and dark current suppression.
Innovation Solution
The image sensor design incorporates a pixel isolation structure with a conductive pattern and buried dielectric pattern in a deep trench, where the isolation dielectric layer's thickness varies with distance from the trench entrance, and the conductive layer is etched back to form a conductive pattern without voids, enhancing step coverage and uniform bias application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel isolation structure is used, then manufacturing process is simple, but image resolution and dark current suppression are poor
Solution Approach 1:
The pixel isolation structure is divided into multiple functional components: a first isolation layer filling the deep trench, a second isolation layer on top of the first isolation layer, and a conductive pattern embedded within. This segmentation allows each layer to perform its specific function optimally, improving image resolution and dark current suppression while maintaining manufacturing feasibility through standardized layering processes.
Solution Approach 2:
The isolation structure extends vertically into a deep trench with significant depth, utilizing the third dimension to improve pixel isolation effectiveness. The multi-layer construction within the vertical dimension provides enhanced isolation performance without increasing lateral footprint, thereby improving image resolution without proportionally increasing overall device complexity.
2Reliability
If conductive layer is deposited to fill deep trench completely, then trench is fully filled, but voids form in the conductive pattern
Solution Approach 1:
The conductive layer is deposited to partially fill the deep trench rather than completely filling it. The first isolation layer is then formed to fill the remaining space. This partial filling approach prevents void formation during deposition while ensuring complete trench filling when combined with the isolation layer, improving conductive pattern uniformity without excessive manufacturing complexity.
Solution Approach 2:
The first isolation layer acts as an intermediary material between the substrate and the conductive pattern. It fills the deep trench and provides a foundation that supports the conductive layer, preventing void formation while ensuring complete filling of the trench structure. This intermediary layer mediates between the conflicting requirements of complete filling and void-free conductive patterns.
3Manufacturing precision
If isolation dielectric layer has uniform thickness, then manufacturing is easier, but step coverage and bias application uniformity are poor
Solution Approach 1:
The isolation dielectric layer is designed with non-uniform thickness, where the first isolation layer has greater thickness at the bottom of the deep trench and tapers toward the top. This local variation in thickness provides optimal step coverage on the trench sidewalls and ensures uniform bias application across the conductive pattern, while still being manufacturable through controlled deposition processes.
Data Source
AI summary
An image sensor comprises a substrate having first and second surfaces opposite to each other, a fixed charge layer in contact with the second surface, an interlayer dielectric layer covering the first surface, a device isolation part adjacent to the first surface in the substrate, and a pixel isolation part in the substrate. The pixel isolation part includes a conductive pattern, a buried dielectric pattern, and an isolation dielectric pattern that is simultaneously in contact with the fixed charge layer and the interlayer dielectric layer. The isolation dielectric layer has a first thickness at a level between the buried dielectric pattern and the conductive pattern. The isolation dielectric layer has a second thickness at a level of a bottom surface of the fixed charge layer. The second thickness is different from the first thickness.