BSI Image Sensor Bond Pad Layout for Sidewall Leakage Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Back-side illuminated (BSI) image sensor devices face etching difficulties due to the large step-height between the device and bond pad regions, leading to potential leakage between adjacent bond pads, which degrades device performance.
Innovation Solution
A method for fabricating BSI image sensors involves forming a substrate with radiation-sensing regions, an interconnect structure on the front surface, and bonding pads that are electrically coupled to the interconnect layers while being separated from the sidewall, ensuring the bonding pads are physically isolated from any residue left on the sidewall during the etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a large step-height is present between device region and bond pad region in BSI image sensor, then the bond pad region can be formed separately, but etching difficulties occur and leakage between adjacent bond pads is induced through sidewall
Solution Approach 1:
A mandrel structure is introduced as an intermediary element during the bond pad formation process. The mandrel serves as a temporary support structure that bridges the large step-height gap between the device region and bond pad region, enabling precise etching and preventing sidewall leakage. After the bond pads are formed, the mandrel is removed, having fulfilled its mediating function during the critical etching stage.
2Productivity
If etching is performed on BSI image sensor with large step-height, then bond pads can be formed, but residue is left on sidewall causing leakage between adjacent bond pads
Solution Approach 1:
The harmful residue that causes leakage between bond pads is selectively removed through a targeted cleaning process. The cleaning solution is applied to specifically target and remove organic residue from the sidewall region without affecting the newly formed bond pads or underlying structures. This extraction of the harmful element restores electrical isolation while preserving the bond pad formation achievements.
Solution Approach 2:
A protective coating is applied to the sidewall region before the etching process to prevent residue formation in the first place. This preliminary protective action creates a barrier that prevents organic materials from adhering to the sidewall during etching, thereby eliminating the source of leakage problems before they can occur.
Data Source
AI summary
Provided is a method of fabricating an image sensor device. An exemplary includes forming a plurality of radiation-sensing regions in a substrate. The substrate has a front surface, a back surface, and a sidewall that extends from the front surface to the back surface. The exemplary method further includes forming an interconnect structure over the front surface of the substrate, removing a portion of the substrate to expose a metal interconnect layer of the interconnect structure, and forming a bonding pad on the interconnect structure in a manner so that the bonding pad is electrically coupled to the exposed metal interconnect layer and separated from the sidewall of the substrate.