Buried Color Filter Array With Thin Spacers for Photodiode Isolation
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Solution Overview
Problem
Standard photolithography methods for forming side walls in color filter arrays consume significant space, compromising the occupancy density and isolation of photodiodes in image sensors.
Innovation Solution
The use of a sacrificial replacement layer and thin spacers with a low refractive index, formed through processes like chemical vapor deposition and dry etching, to create a fully buried color filter array that improves photodiode isolation without occupying excessive area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard photolithography methods are used to form side walls between color filters, then color filter isolation is achieved, but occupancy density deteriorates due to substantial space consumption by side walls
Solution Approach 1:
The patent changes the physical parameters of the spacer material by selecting materials with low refractive indices (e.g., air, fluorinated polymers, silicon oxide with specific refractive indices). This parameter change allows the spacers to reflect rather than absorb light, maintaining isolation functionality while reducing the required spacer thickness and footprint area, thereby improving occupancy density without compromising color filter isolation
Solution Approach 2:
The patent applies different material properties to different parts of the spacer structure. The spacers are designed with specific local optical properties (low refractive index) at their interfaces with color filters to optimize light reflection, while maintaining structural integrity through appropriate material selection and thickness control. This local optimization allows minimal space occupation while achieving effective light isolation between adjacent color filters
2Reliability
If thicker spacers are used to improve light isolation between color filters, then color filter isolation is enhanced, but occupancy density worsens due to increased area consumption
Solution Approach 1:
The patent fundamentally changes the optical parameter of the spacer material by selecting materials with low refractive indices. This parameter change transforms the light interaction mechanism from absorption (in high refractive index materials) to reflection (in low refractive index materials), enabling effective light isolation with much thinner spacer structures, thereby reducing occupancy density while maintaining or enhancing light isolation performance
Solution Approach 2:
The patent substitutes the traditional mechanical/isolation-based approach (relying on physical thickness for light blocking) with an optical approach (using refractive index differences for light reflection). This substitution allows the spacers to achieve light isolation functionality through optical properties rather than purely mechanical dimensions, enabling thinner structures that occupy less area while maintaining effective isolation between color filters
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 color filter isolation and density, allowing more photons to reach photodiodes while maintaining high occupancy density, thus improving the angular response and quantum efficiency of image sensors.
Implementation Method 1
The sacrificial replacement layer may be made of a material that is selectively removable by a chemical etch process
Implementation Method 2
The use of a sacrificial replacement layer and thin spacers with a low refractive index, formed through processes like chemical vapor deposition
Implementation Method 3
formed through processes like chemical vapor deposition and dry etching
Implementation Method 4
using thin spacers that reflect photons rather than absorbing them, thus preventing light corruption
Data Source
AI summary
An image sensor includes a substrate. An array of photodiodes is disposed in the substrate. A plurality of spacers is arranged in a spacer pattern. At least one spacer of the plurality of spacers has an aspect ratio of 18:1 or greater. A buffer layer is disposed between the substrate and the spacer pattern. An array of color filters is disposed in the spacer pattern.