BSI Image Sensor Backside HA Structure for Low Reflectance
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Solution Overview
Problem
Backside illumination (BSI) image sensor chips face issues with non-optically generated signals such as leakage and dark currents, which require calibration, and existing methods do not effectively reduce reflectance and optical cross-talk, impacting quantum efficiency.
Innovation Solution
A high absorption (HA) structure is formed on the backside of the BSI image sensor to reduce reflectance and improve absorption of incident electromagnetic radiation, combined with optimized process steps that include a metal grid and anti-reflective coatings to enhance optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metal shield is formed on the backside to block light for black reference image sensors, then non-optically generated signals can be calibrated, but reflectance reduction and optical cross-talk minimization are insufficient
Solution Approach 1:
The patent applies composite materials by combining multiple layers including anti-reflective coatings (such as silicon oxide, silicon nitride, or silicon oxynitride), metal grids (aluminum, copper, or tungsten), and high absorption structures on the backside of the semiconductor substrate. This multi-layer composite structure simultaneously achieves light blocking for calibration while providing reflectance reduction and optical cross-talk minimization, resolving the contradiction between calibration accuracy and optical performance.
Solution Approach 2:
The patent implements local quality by applying different structures to different regions: the black reference image sensor region receives a metal shield and anti-reflective coating for light blocking, while the active pixel regions receive high absorption structures and metal grids optimized for reducing reflectance and optical cross-talk. This localized differentiation allows each region to have optimal properties for its specific function, achieving both calibration accuracy and optical performance.
2Ease of manufacture
If the backside surface is left flat and unprocessed, then manufacturing is simpler, but reflectance is high and quantum efficiency is reduced
Solution Approach 1:
The patent applies segmentation by dividing the backside surface into multiple functional zones: regions with high absorption structures (such as protrusions or trenches), regions with anti-reflective coatings, and regions with metal grids. This segmentation allows each zone to contribute specifically to light absorption while maintaining a systematic manufacturing process that, although more complex than a flat surface, follows a structured approach to achieving high quantum efficiency.
Solution Approach 2:
The patent implements parameter changes by modifying the physical and optical parameters of the backside surface through anti-reflective coatings (changing refractive index and surface properties), metal grid patterns (changing electrical and optical parameters), and high absorption structures (changing surface geometry). These parameter modifications significantly reduce reflectance and enhance light absorption, improving quantum efficiency while maintaining manufacturability through established semiconductor processing techniques.
3Device complexity
If optical cross-talk is not minimized, then device structure can be simpler, but signal accuracy between adjacent pixels deteriorates
Solution Approach 1:
The patent employs intermediaries by introducing metal grids and isolation structures between adjacent active pixels and between active pixels and black reference sensors. These intermediary structures act as optical and electrical barriers that prevent cross-talk while maintaining a relatively simple overall device architecture. The metal grids serve dual functions as intermediaries for both optical isolation and electrical connectivity, achieving signal accuracy without excessive structural complexity.
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 HA structure significantly reduces reflectance, improves quantum efficiency, and minimizes optical cross-talk, leading to enhanced performance in both visible and near-infrared regimes.
Implementation Method 1
A high absorption (HA) structure is formed on the backside of the BSI image sensor to reduce reflectance and improve absorption of incident electromagnetic radiation
Implementation Method 2
combined with optimized process steps that include a metal grid and anti-reflective coatings to enhance optical performance
Data Source
AI summary
A backside illumination (BSI) image sensor and a method of forming the same are provided. A device includes a substrate and a plurality of photosensitive regions in the substrate. The substrate has a first side and a second side opposite to the first side. The device further includes an interconnect structure on the first side of the substrate, and a plurality of recesses on the second side of the substrate. The plurality of recesses extend into a semiconductor material of the substrate.