Reflective Guide Layer in BSI Image Sensor Recesses
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Solution Overview
Problem
Backside illuminated (BSI) image sensors face challenges in optimizing light path efficiency and reducing cross-talk between pixels, which affects their sensitivity and noise immunity.
Innovation Solution
The implementation of a reflective guide layer and color filters in recesses over a substrate with a conformal reflective guide material, forming a grid structure that directs light to photo diodes while minimizing optical path lengths and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional BSI image sensor structure is used, then light sensitivity and quantum efficiency are limited, but adding a reflective guide layer and color filters in recesses increases device complexity
Solution Approach 1:
The sensor surface is segmented into recesses and non-recess areas, with reflective guide layers selectively formed in the recesses. This segmentation allows different regions to serve different functions: recesses with reflective guides for enhanced light collection, and non-recess areas for other pixel functions, thereby improving light sensitivity without uniformly increasing complexity across the entire device.
Solution Approach 2:
The reflective guide layer is applied locally only in specific recess regions rather than uniformly across the entire sensor surface. This local application targets areas where light collection enhancement is most needed, improving quantum efficiency in those specific locations while minimizing the overall increase in device complexity and manufacturing steps.
2Object-affected harmful factors
If light path length is reduced to minimize cross-talk, then optical efficiency improves, but light sensitivity may be compromised
Solution Approach 1:
The reflective guide layer is positioned on the sidewalls of recesses, utilizing the vertical dimension and lateral surfaces rather than only horizontal planes. This three-dimensional configuration allows light to be reflected from multiple angles and paths, directing it toward the photo diode while maintaining a compact overall structure that minimizes cross-talk between adjacent pixels.
Solution Approach 2:
The reflective guide layer acts as an intermediary optical element that redirects light paths. It intercepts light that would otherwise travel laterally causing cross-talk, and reflects it downward toward the photo diode. This intermediary structure effectively manages light propagation, reducing harmful cross-talk while enhancing useful light collection.
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 configuration improves light sensitivity, reduces cross-talk, and increases quantum efficiency, achieving a signal-to-noise ratio of 10 dB and better color shading uniformity.
Implementation Method 1
The implementation of a reflective guide layer and color filters in recesses over a substrate with a conformal reflective guide material, forming a grid structure that directs light to photo diodes
Data Source
AI summary
Various structures of image sensors are disclosed, as well as methods of forming the image sensors. According to an embodiment, a structure comprises a substrate comprising photo diodes, an oxide layer on the substrate, recesses in the oxide layer and corresponding to the photo diodes, a reflective guide material on a sidewall of each of the recesses, and color filters each being disposed in a respective one of the recesses. The oxide layer and the reflective guide material form a grid among the color filters, and at least a portion of the oxide layer and a portion of the reflective guide material are disposed between neighboring color filters.