Transparent Substrate Micro Lens Image Sensor Fabrication
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Solution Overview
Problem
Front-side illuminated image sensors face inefficiencies due to light obstruction by metal layers, and backside illuminated sensors are more complex and costly to manufacture, while current solutions for improving front-side sensors are limited by surface roughness and manufacturing costs.
Innovation Solution
A method involving a transparent substrate with recessed micro lenses and a color filter formed on an independent substrate, which is then engaged with the image sensing device, allowing for deeper embedding and improved optical performance without increasing manufacturing complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a front-side illuminated image sensor is used, then the manufacturing process is simpler and cost is lower, but the quantum efficiency is reduced due to light obstruction by metal layers
Solution Approach 1:
The patent divides the color filter structure into multiple segments: a first color filter layer embedded in the substrate, and a second color filter layer formed on the first color filter layer. This segmentation allows the light to pass through the first layer to reach the sensor array while the second layer provides additional color filtering, thereby improving quantum efficiency without requiring a complete switch to backside illumination architecture
Solution Approach 2:
The patent extends the color filter structure in the vertical dimension by embedding the first color filter layer within the substrate at different depths, and stacking the second color filter layer on top. This multi-layer vertical arrangement enables effective light filtering while maintaining front-side illumination geometry, resolving the contradiction between manufacturing simplicity and optical performance
2Reliability
If a backside illuminated image sensor is used, then the quantum efficiency is improved by eliminating metal layer obstruction, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent performs preliminary embedding of the first color filter layer into the substrate before forming the second color filter layer and completing the sensor assembly. This preliminary action allows the color filtering function to be established early in the manufacturing process, improving quantum efficiency without requiring the complex substrate thinning and handle wafer removal procedures associated with backside illumination sensors
Solution Approach 2:
The patent creates a simplified copy of the backside illumination optical performance by using a multi-layer color filter structure on the front side that achieves similar light filtering effectiveness. This copying approach replicates the optical benefits of backside illumination while maintaining the manufacturing simplicity of front-side illumination architecture
3Reliability
If the color filter embedding depth is increased to improve optical performance, then the quantum efficiency improves, but the surface roughness and unevenness increase adversely affecting subsequent process and yield
Solution Approach 1:
The patent segments the color filter functionality across multiple layers with different embedding depths. The first color filter layer is embedded at a controlled depth within the substrate, while the second color filter layer is formed on the surface. This segmentation allows each layer to contribute to color filtering without requiring excessive embedding depth, thereby maintaining surface planarity and avoiding the roughness problems associated with deep embedding
Solution Approach 2:
The patent uses a partial embedding approach where the first color filter layer is embedded to a moderate depth that provides sufficient optical filtering effect, rather than embedding it completely or excessively deep. This partial action achieves the necessary quantum efficiency improvement while maintaining surface quality for subsequent manufacturing processes
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 enhances quantum efficiency and reduces manufacturing costs for front-side illuminated image sensors, achieving performance comparable to backside illuminated sensors while simplifying the packaging process and addressing surface roughness issues.
Implementation Method 1
a transparent substrate with recessed micro lenses
Data Source
AI summary
A method for fabricating an image sensor, wherein the method comprises steps as follows: Firstly, a transparent substrate is formed on a working substrate. Pluralities of micro lens are formed in the transparent substrate, wherein the lenses have a refraction ratio differing from that of the transparent substrate. Subsequently, a color filter is formed on the lenses. Afterward, the color filter is engaged with an image sensing device by flipping around the working substrate.