Backside Illuminated Global Shutter Pixels Shielding Parasitic Light
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Solution Overview
Problem
Backside illuminated global shutter image sensors face challenges in shielding storage diodes from parasitic light, leading to inefficiencies and image artifacts like vertical shading and moving object smear, as conventional solutions are not applicable due to the illumination configuration.
Innovation Solution
Incorporating shielding structures such as opaque layers and deep trench isolation structures between photodiodes in the backside illuminated image sensors to prevent light from reaching the storage diodes, including configurations like backside deep trench isolation, frontside deep trench isolation, and metal-filled trenches, which effectively reflect or absorb incident light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frontside illuminated pixels with shielding layers in dielectric stack are used to shield storage diodes from parasitic light, then storage diode shielding is improved, but pixel performance is limited compared to backside illuminated pixels
Solution Approach 1:
The patent inverts the conventional frontside illumination approach by implementing backside illumination. Instead of placing photodiodes at the front surface with shielding layers above storage diodes, the photodiodes are positioned at the back surface of the substrate, allowing light to enter from the backside. This inversion eliminates the need for complex dielectric stack shielding while achieving superior parasitic light rejection and overall pixel performance.
Solution Approach 2:
The patent transitions from two-dimensional planar shielding layers in the dielectric stack to three-dimensional deep trench isolation structures that extend vertically through the substrate. This dimensional change creates effective light blocking paths without interfering with the optical path to photodiodes, solving the contradiction between shielding effectiveness and pixel performance.
2Reliability
If backside illuminated pixels are used to improve performance, then pixel efficiency is enhanced, but storage diodes become vulnerable to parasitic light scattering and diffraction
Solution Approach 1:
The patent introduces deep trench isolation structures filled with opaque material as intermediary elements between the storage diodes and incident light. These trenches act as mediators that block parasitic light paths without interfering with the functional operation of backside illuminated photodiodes, thereby protecting storage diodes while maintaining high pixel efficiency.
Solution Approach 2:
The patent extracts and removes the problematic parasitic light paths by creating deep trenches that physically separate and isolate storage diodes from incoming light. This extraction of harmful light paths allows backside illuminated pixels to maintain high efficiency while preventing parasitic light exposure to storage diodes.
3Object-affected harmful factors
If conventional global shutter pixels with dielectric stack shielding are used, then storage diodes are protected from parasitic light, but manufacturing complexity increases due to additional shielding layers
Solution Approach 1:
The patent extracts and removes the complex dielectric stack shielding structure by transitioning to backside illumination with deep trench isolation. This extraction eliminates multiple metal routing lines and vias that were previously needed for shielding, significantly reducing manufacturing complexity while maintaining effective parasitic light protection.
Solution Approach 2:
By inverting to backside illumination, the patent eliminates the need for complex frontside dielectric stack shielding. The inversion simplifies the overall structure by removing multiple shielding layers, metal routing lines, and vias, thereby reducing device complexity while achieving superior parasitic light shielding through the backside illumination geometry itself.
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 proposed shielding structures significantly enhance the efficiency of backside illuminated global shutter image sensors by minimizing light interference, reducing image artifacts, and improving overall performance compared to frontside illuminated pixels.
Implementation Method 1
an opaque layer formed in a trench between first and second backside deep trench isolation structures... effectively reflect or absorb incident light
Implementation Method 2
shielding structures formed in the substrate over the charge storage region... effectively reflect or absorb incident light
Data Source
AI summary
Global shutter imaging pixels may include a charge storage region that receives charge from a respective photodiode. Global shutter imaging pixels may be formed as frontside illuminated imaging pixels or backside illuminated imaging pixels. Shielding charge storage regions from incident light may be important for image sensor performance. To shield charge storage regions in backside illuminated global shutter imaging pixels, shielding structures may be included over the charge storage region. The shielding structures may include backside trench isolation structures, a metal layer formed in a backside trench between backside trench isolation structures, and frontside deep trench isolation structures. The metal layer may have angled portions that reflect light towards the photodiodes.