Image Sensor Microlens Striation Suppression via Trench Planarization
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Solution Overview
Problem
In image sensor manufacturing, the current methods for forming microlenses result in striation due to a planar offset between the scribe line and the pixel region, leading to non-uniform microlens thickness and reduced sensitivity, especially at the edges of the pixel region.
Innovation Solution
The formation of a trench in the interlayer dielectric above the pixel region, followed by a color filter and a planarization layer, ensures that the microlens is formed with the top surface of the interlayer dielectric and the underside of the microlens at the same height, reducing the height difference and inhibiting striation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photolithography process using special photoresist for microlenses is performed, then microlenses can be formed, but striation occurs due to planar offset between scribe line and pixel region
Solution Approach 1:
A planarization layer is formed in advance before forming the microlens to pre-compensate for the height difference between the scribe line and pixel region. This preliminary action ensures that the photoresist can be uniformly applied across the entire surface without being affected by the underlying topography, thereby preventing striation during the photolithography process.
Solution Approach 2:
The planarization layer acts as an intermediary between the uneven substrate (with scribe line offset) and the photoresist layer. It provides a flat intermediate surface that allows uniform photoresist coating and subsequent uniform microlens formation, while still allowing the microlens to focus light correctly onto the pixel region below.
2Ease of manufacture
If height difference at border between scribe line and pixel region exists, then planar offset occurs, but microlens thickness becomes non-uniform
Solution Approach 1:
The planarization layer is formed before the microlens to pre-compensate for height differences, enabling uniform photoresist application and consistent microlens thickness across the entire pixel region including areas near the scribe line border.
Solution Approach 2:
The planarization layer is selectively formed only in the pixel region where uniformity is needed, while leaving the scribe line area unchanged. This localized approach maintains ease of manufacture by not requiring global substrate modification, while achieving uniform microlens thickness where required.
3Reliability
If microlens thickness varies in pixel region, then focal points become different, but sensitivity decreases especially at edge
Solution Approach 1:
By forming the planarization layer before the microlens, the invention ensures uniform photoresist thickness and consequently uniform microlens thickness across the entire pixel region. This uniformity ensures that all microlenses have the same focal point, preventing cross-talk between adjacent pixels and reducing noise, especially at the edges where the scribe line offset would otherwise cause variations.
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
This approach suppresses striation and enhances the sensitivity of the microlenses by maintaining uniformity and reducing noise, thereby improving the overall performance of the image sensor.
Implementation Method 1
The formation of a trench in the interlayer dielectric above the pixel region, followed by a color filter and a planarization layer, ensures that the microlens is formed with the top surface of the interlayer dielectric and the underside of the microlens at the same height, reducing the height difference and inhibiting striation
Data Source
AI summary
An image sensor and a method for manufacturing the same are provided. The image sensor comprises a pixel region defined on a substrate, an interlayer dielectric on the substrate and comprising a trench above the pixel region, a color filter within the trench, and a microlens on the color filter.