Recessed Bond Pad Structure for Flat FSI Image Sensor Topography
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Solution Overview
Problem
Conventional bond pads in CMOS image sensors, formed directly on copper interconnect layers within low-k dielectric layers, are structurally weak and prone to deformation or cracking, and the use of passivation layers to enhance structural support results in topography issues that negatively impact image sensor performance by causing photoresist non-uniformity and depth of focus problems during color filter formation.
Innovation Solution
A bond pad is arranged within a recess in a passivation structure over the dielectric structure, with protrusions extending through openings to contact the underlying metal interconnect layers, mitigating stress on the interconnect layers and maintaining a flat surface topography that does not interfere with color filter formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If passivation layers are added to enhance structural support for bond pads, then the structural strength is improved, but topography uniformity deteriorates causing photoresist non-uniformity and depth of focus problems
Solution Approach 1:
The bond pad structure is segmented into multiple functional layers: a recessed region in the passivation layer, a bond pad material layer filling the recess, and protrusions extending through openings. This segmentation allows the bond pad to have both structural support (from the recess and passivation layer) and flat topography (from the surface layer), resolving the contradiction between strength and uniformity
Solution Approach 2:
Different regions of the bond pad structure have different properties: the recessed region provides structural support and stress relief, while the surface layer maintains flat topography for uniform photoresist coating. The protrusions through openings provide localized electrical connection points. This local differentiation of properties resolves the contradiction between needing structural strength and maintaining topography uniformity
2Device complexity
If bond pads are formed directly on copper interconnect layers within low-k dielectric layers, then device complexity is reduced, but reliability deteriorates due to deformation and cracking
Solution Approach 1:
The bond pad structure acts as an intermediary between the copper interconnect layers and the external bonding process. The recessed configuration and protrusions through openings provide a buffered interface that protects the underlying copper interconnects from direct mechanical stress during bonding, preventing deformation and cracking while maintaining electrical connection
Solution Approach 2:
The recessed structure of the bond pad, with its sidewalls and protected configuration, provides beforehand cushioning against mechanical stress during the bonding process. This pre-configured protective structure absorbs and distributes stress before it can reach the vulnerable copper interconnect layers, preventing damage in advance
Data Source
AI summary
The present disclosure relates to a semiconductor structure. The semiconductor structure includes a dielectric layer having a first dielectric surface and a second dielectric surface opposite to the first dielectric surface. The dielectric layer defines a recess in the first dielectric surface, and the recess includes a sidewall of the dielectric layer. A first conductive layer contacts a bottom surface of the dielectric layer. The sidewall of the dielectric layer is directly over the first conductive layer. A second conductive layer contacts the first conductive layer and the dielectric layer. The second conductive layer vertically extends from the first conductive layer to above the dielectric layer. A third conductive layer contacts the second conductive layer. The third conductive layer is laterally separated from a sidewall of the second conductive layer that faces the third conductive layer by a non-zero distance.