Curved Image Sensor Spacer Profile for Edge Resolution
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Solution Overview
Problem
Chemical mechanical polishing (CMP) in image sensor fabrication is less precise and can induce defects such as pitting and scratches on semiconductor wafers, limiting the optimization of pixel circuitry and optical performance.
Innovation Solution
A curved image sensor design is implemented, where a spacer layer with a concave cross-sectional profile is used, with harder dye-edge structures resisting CMP, allowing for controlled thinning and planarization, thereby minimizing optical defects and enhancing edge resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical polishing (CMP) is used to thin and planarize the wafer, then the wafer can be thinned and surfaces can be planarized, but defects such as pitting and scratches are induced on the wafer surface
Solution Approach 1:
The patent applies this principle by using the CMP-induced dishing effect beneficially. The spacer layer is intentionally designed to be consumed during CMP, creating a concave profile that positions the photodiodes at the optimal focal plane. The harmful CMP roughness is mitigated by subsequent planarization steps, while the beneficial dishing profile is retained for optical focusing.
Solution Approach 2:
The patent changes the physical parameters of the spacer layer by selecting materials with different CMP removal rates. The spacer layer uses materials (oxides, nitrides, polymers) that are selectively removed at controlled rates during CMP, enabling precise thickness control and profile formation. This parameter control allows the spacer to self-adjust the photodiode positioning without requiring additional lithography steps.
2Ease of manufacture
If the sensor is made flat, then manufacturing is simpler, but edge resolution is degraded due to mismatch with curved optical lens focal plane
Solution Approach 1:
The patent introduces curvature into the sensor structure by forming a concave profile in the spacer layer. This curvature matches the spherical focal plane of the optical lens, ensuring that photodiodes across the entire sensor array (including edges) are positioned at the correct focal distance. The curved profile is achieved through controlled CMP consumption of the spacer material, combining manufacturing simplicity with optical precision.
3Ease of manufacture
If photodiodes are positioned at uniform depth in a flat sensor, then manufacturing is easier, but optical focusing is degraded at sensor edges
Solution Approach 1:
The patent applies local quality by creating a non-uniform spacer layer thickness profile. The spacer thickness varies across the sensor array, being thicker at the edges and thinner at the center, which compensates for the curved focal plane of the lens. This local variation in spacer thickness positions each photodiode at its optimal focal depth, with edge photodiodes requiring greater spacing than center photodiodes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The curved image sensor design improves edge resolution and minimizes optical defects by aligning the curvature of the sensor with the optical lens, ensuring focused image light is efficiently passed through the photodiodes, addressing the limitations of traditional flat sensor designs.
Implementation Method 1
Chemical mechanical polishing (CMP) is integral to semiconductor device fabrication. It can be used to thin wafers, remove excess deposition flux, and planarize surfaces. Since CMP may be less precise than other fabrication techniques and is generally rougher on the semiconductor wafers, CMP may induce defects into electronic devices if not properly controlled.
Implementation Method 2
A curved image sensor design is implemented, where a spacer layer with a concave cross-sectional profile is used, with harder dye-edge structures resisting CMP, allowing for controlled thinning and planarization
Implementation Method 3
The curved image sensor design improves edge resolution and minimizes optical defects by aligning the curvature of the sensor with the optical lens, ensuring focused image light is efficiently passed through the photodiodes
Data Source
AI summary
An image sensor includes a plurality of photodiodes arranged in an array and disposed in a semiconductor material with pinning wells disposed between individual photodiodes in the plurality of photodiodes. The image sensor also includes a microlens layer. The microlens layer is disposed proximate to the semiconductor material and is optically aligned with the plurality of photodiodes. A spacer layer disposed between the semiconductor material and the microlens layer. The spacer layer has a concave cross-sectional profile across the array, and the microlens layer is conformal with the concave cross-sectional profile of the spacer layer.