BSI Image Sensor Pad Structure With Rounded Recess Corners
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Solution Overview
Problem
Existing methods for forming pad structures in back side illuminated (BSI) image sensor devices often result in deep recesses that can lead to voids in dielectric layers, causing interconnection issues such as increased contact resistance and electromigration due to acid or etchant penetration.
Innovation Solution
A spacer layer with a tapered profile is formed around the corners of the recess where the pad structure is created, effectively rounding off the recess profile and preventing void formation when depositing a dielectric layer, resulting in more reliable pad and interconnect structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If deep recesses are formed for pad structures in BSI image sensor devices, then pad structure formation is enabled, but voids form in dielectric layers causing interconnection issues
Solution Approach 1:
The patent applies curvature by rounding the corners of the recess through a multi-step process: first forming a spacer layer around the recess corners, then selectively removing portions of the spacer layer to create rounded corners. This curvature prevents void formation in the dielectric layer during subsequent deposition processes, thereby maintaining interconnection reliability while still enabling pad structure formation.
2Ease of manufacture
If deep recesses are formed for pad structures, then pad structures can be created, but contact resistance increases due to void formation
Solution Approach 1:
By rounding the recess corners through the spacer layer process, the patent eliminates sharp corners that cause void formation during dielectric deposition. This ensures continuous, void-free dielectric layers over the pad structures, maintaining low and consistent contact resistance while enabling pad structure creation in deep recesses.
3Ease of manufacture
If deep recesses are formed for pad structures, then pad structures can be established, but electromigration occurs due to etchant penetration
Solution Approach 1:
The rounded corners created by the spacer layer process eliminate sharp geometric features that facilitate etchant penetration and acid accumulation. This curvature modification prevents the formation of pathways for harmful substances to reach the pad structures and interconnects, thereby preventing electromigration and maintaining long-term reliability.
Data Source
AI summary
A device is disclosed. The device includes a plurality of pixels disposed over a first surface of a semiconductor layer. The device includes a device layer disposed over the first surface. The device includes metallization layers disposed over the device layer. One of the metallization layers, closer to the first surface than any of other ones of the metallization layers, includes at least one conductive structure. The device includes an oxide layer disposed over a second surface of the semiconductor layer, the second surface being opposite to the first surface, the oxide layer also lining a recess that extends through the semiconductor layer. The device includes a spacer layer disposed between inner sidewalls of the recess and the oxide layer. The device includes a pad structure extending through the oxide layer and the device layer to be in physical contact with the at least one conductive structure.