Dual-Layer Micro-Lens CMOS Image Sensor Focusing
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Solution Overview
Problem
The existing manufacturing method for CMOS image sensors is plagued by unstable patterning conditions of photosensitive resist patterns, which degrade the focusing efficiency of light and reduce the operational performance of the image sensor.
Innovation Solution
The method involves forming first micro-lenses in trenches on a planarization layer over photodiodes and wrapping them with second micro-lenses, made of different materials with varying refractive indices, to enhance the focusing capability by improving the curvature and structure of the micro-lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer micro-lens structure is used, then the manufacturing process is simple, but the focusing efficiency of light is insufficient
Solution Approach 1:
The micro-lens is divided into two distinct layers: a first micro-lens layer formed directly over the photodiode, and a second micro-lens layer formed over the first layer. This segmentation allows each layer to be optimized for specific functions, with the first layer providing base focusing and the second layer enhancing the focusing efficiency, thereby resolving the contradiction between manufacturing simplicity and focusing performance.
Solution Approach 2:
The dual-layer micro-lens structure employs different materials for each layer, where the first micro-lens layer uses a photosensitive resist material and the second micro-lens layer uses a different material with optimized optical properties. This composite approach enables tailored refractive indices and curvatures for each layer, maximizing light focusing efficiency while maintaining manufacturability through established deposition and patterning techniques.
2Manufacturing precision
If the micro-lens curvature is increased to improve focusing, then light focusing efficiency improves, but the patterning stability of photosensitive resist deteriorates
Solution Approach 1:
By segmenting the micro-lens into two layers with different materials and curvatures, the patent distributes the focusing function across layers. The first layer provides a stable, moderately curved base structure formed by standard photosensitive resist patterning, while the second layer adds the necessary additional curvature for high focusing efficiency. This segmentation prevents the photosensitive resist from needing to form excessively high curvatures that would compromise patterning stability.
Solution Approach 2:
The first micro-lens layer acts as an intermediary between the photodiode and the second micro-lens layer. It provides a stable foundation with moderate curvature that does not stress the photosensitive resist patterning process, while still contributing to the overall focusing function. This intermediary layer enables the second layer to achieve the required high curvature for optimal focusing without compromising the stability of the underlying structure.
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 configuration increases the focusing efficiency of light, allowing more light to be focused onto photodiodes, resulting in improved image sensor performance and vivid color acquisition, while simplifying the reworking process and reducing manufacturing costs.
Implementation Method 1
The micro-lenses are located over the photodiodes to refract the paths of incident light rays, thereby allowing a greater amount of light to reach the photodiodes.
Implementation Method 2
The micro-lenses refract light rays running parallel to an optical axis of the micro-lens to a predetermined focal point on the optical axis.
Data Source
AI summary
Disclosed are a CMOS image sensor capable of improving the focusing capability of light and a method for manufacturing the same. The CMOS image sensor includes a plurality of first micro-lenses formed in the upper part of the planarization layer, each of the first micro-lenses arranged over a corresponding photodiode, and a plurality of second micro-lenses formed on the planarization layer, each of the plurality of second micro-lenses wrapping a corresponding first micro-lens respectively.