Low-Refractivity Polymer Grid for BSI Sensor Crosstalk Reduction
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Solution Overview
Problem
Existing semiconductor image sensors, particularly Backside Illumination (BSI) CMOS image sensors, face challenges in maximizing quantum efficiency (QE) and reducing light crosstalk due to refractive index mismatches between different layers and materials, which affect image quality.
Innovation Solution
A low-refractivity polymer grid structure is formed on the backside of a semiconductor substrate with color filters having higher refractivity, enabling total reflection of light and reducing crosstalk by aligning grid structures vertically and using materials with similar thermal expansion coefficients to minimize delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional grid structures with higher refractivity materials are used, then light reflection is enhanced, but refractive index mismatch between layers increases causing delamination and manufacturing defects
Solution Approach 1:
The patent changes the refractive index parameter of the grid structure material from conventional high refractivity materials to low refractivity materials with a refractive index of 1.3 or less. This parameter change reduces the refractive index mismatch between the grid structure and surrounding layers, thereby reducing delamination while maintaining adequate light reflection through the low-refractivity material's optical properties
Solution Approach 2:
The patent employs composite material structures where the grid structure is formed from low-refractivity materials (such as specific polymers or dielectric materials) that are optically matched with adjacent layers. This composite approach allows optimization of both optical performance and mechanical adhesion by selecting materials with compatible refractive indices and thermal expansion coefficients
2Ease of manufacture
If materials with different thermal expansion coefficients are used for grid structure and color filters, then manufacturing flexibility is improved, but delamination occurs due to thermal stress
Solution Approach 1:
The patent specifies selecting low-refractivity materials with refractive indices of 1.3 or less and explicitly requires matching thermal expansion coefficients between the grid structure material and color filter material. This parameter specification ensures that both optical performance and thermal stability are achieved, preventing delamination during manufacturing and operation while maintaining manufacturing flexibility
3Use of energy by moving object
If refractive index mismatch is increased to enhance light reflection, then quantum efficiency improves, but crosstalk between adjacent pixels increases
Solution Approach 1:
The patent changes the refractive index parameter to 1.3 or less for the grid structure material, which optimizes the refractive index contrast with color filters to enhance light reflection and quantum efficiency. Simultaneously, this parameter change reduces excessive refractive index mismatch that would cause harmful light crosstalk between adjacent pixels, achieving a balance between QE enhancement and crosstalk reduction
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
The solution enhances quantum efficiency by optimizing light reflection and reduces crosstalk, thereby improving image sensor performance and quality.
Implementation Method 1
enabling total reflection of light and reducing crosstalk
Data Source
AI summary
A method includes forming image sensors in a semiconductor substrate, thinning the semiconductor substrate from a backside of the semiconductor substrate, forming a dielectric layer on the backside of the semiconductor substrate, and forming a polymer grid on the backside of the semiconductor substrate. The polymer grid has a first refractivity value. The method further includes forming color filters in the polymer grid, wherein the color filters has a second refractivity value higher than the first refractivity value, and forming micro-lenses on the color filters.