CMOS Image Sensor Trench Fabrication for Light Path Reduction
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Solution Overview
Problem
Conventional methods for fabricating CMOS image sensors result in increased light path to photodiodes and peeling issues with color filters, affecting sensor performance.
Innovation Solution
A method involving a patterned photomask for forming trenches in the passivation layer, depositing color filters within these trenches, and using the same photomask to create microlenses on a planarizing layer, reducing light path and preventing filter peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If color filters are formed directly on the surface of the passivation layer, then the fabrication process is simplified, but the light path to photodiodes increases and color filter peeling occurs
Solution Approach 1:
The invention divides the passivation layer into multiple regions by forming trenches, creating separate zones for color filters and microlenses. This segmentation allows color filters to be positioned in trenches rather than on the flat surface, preventing peeling while maintaining fabrication efficiency through patterned photomask alignment.
Solution Approach 2:
The invention transitions from a two-dimensional surface arrangement to a three-dimensional structure by forming trenches in the passivation layer. Color filters are placed within these trenches, creating vertical separation that reduces the light path to photodiodes and prevents peeling, while microlenses are formed on the planarized surface above.
2Ease of manufacture
If color filters are formed on the passivation layer surface, then fabrication is easier, but light path to photodiodes increases
Solution Approach 1:
By segmenting the passivation layer into trenches, the invention creates a stepped structure that positions color filters closer to the photodiodes. This segmentation reduces the vertical distance light must travel through the passivation layer, thereby shortening the light path while maintaining ease of fabrication through patterned alignment.
Solution Approach 2:
The invention uses vertical dimensionality by forming trenches to position color filters at different heights relative to the passivation layer surface. This three-dimensional arrangement reduces the effective light path length through the passivation layer compared to a flat surface configuration.
3Ease of manufacture
If color filters are formed on the passivation layer, then fabrication is simpler, but peeling of color filters occurs
Solution Approach 1:
The invention segments the passivation layer by forming trenches, creating physical anchors for color filters. This segmentation provides mechanical interlocking that prevents peeling, while the trench structure maintains fabrication simplicity through patterned photomask alignment and planarized surface formation.
Solution Approach 2:
By transitioning from a two-dimensional surface placement to a three-dimensional trench structure, the invention creates vertical walls that provide adhesion surfaces for color filters. This dimensional change enhances adhesion stability through increased contact area and mechanical interlocking, while maintaining fabrication simplicity.
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 reduces light path to photodiodes and prevents color filter peeling, enhancing image sensor performance by aligning microlenses with color filters and allowing for efficient light separation.
Implementation Method 1
using a patterned photomask to perform a first pattern transfer process for forming a plurality of trenches corresponding to each photodiode in the passivation layer
Implementation Method 2
using the patterned photomask to perform a second pattern transfer process for forming a plurality of microlenses corresponding to each color filter on the planarizing layer
Implementation Method 3
forming a plurality of microlenses corresponding to each color filter on the planarizing layer... reducing light path to photodiodes
Implementation Method 4
The CMOS image sensor separates (i.e., classifies) incident light into a combination of light of different wavelengths... a monochromatic color filter array (CFA) must be set above every optical sensor element
Data Source
AI summary
A method for fabricating image sensor is disclosed. The method includes the steps of: providing a substrate, wherein the substrate comprises a plurality of photodiodes; forming at least one dielectric layer and a passivation layer on surface of the substrate; using a patterned photomask to perform a first pattern transfer process for forming a plurality of trenches corresponding to each photodiode in the passivation layer; forming a plurality of color filters in the trenches; covering a planarizing layer on the color filters; and using the patterned photomask to perform a second pattern transfer process for forming a plurality of microlenses corresponding to each color filter on the planarizing layer.