BSI Image Sensor Micro-Pillar Structure for Higher Quantum Efficiency
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Solution Overview
Problem
Backside illuminated (BSI) solid-state image sensors face challenges in maintaining performance as they shrink in size, leading to reduced quantum efficiency and increased dark current and noise due to reflection of incident light and integrated circuitry complexity.
Innovation Solution
A novel BSI image sensor structure featuring micro pillars with a gradually decreasing refractive index and recesses with specific shapes, such as diamond-shaped bottoms, is introduced to reduce light reflection and enhance diffraction, combined with a method of fabricating these features using photolithography and wet etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If BSI image sensor is shrunk to smaller pixel pitch, then device size is reduced, but quantum efficiency deteriorates and dark current increases
Solution Approach 1:
The patent applies curvature by forming micro-pillars with rounded tops and diamond-shaped recesses with curved {111} crystallographic planes on the light-receiving surface. This curved micro-structure increases the optical path length of incident light through multiple internal reflections, enhancing light absorption and quantum efficiency in the miniaturized BSI sensor without increasing device size.
Solution Approach 2:
The patent introduces a vertical dimension by creating three-dimensional micro-pillar structures with recesses extending into the semiconductor layer. This vertical micro-structure manipulates light propagation in the depth direction, increasing the effective light path length and improving quantum efficiency despite reduced pixel pitch in the planar dimensions.
2Volume of moving object
If BSI image sensor is shrunk to smaller pixel pitch, then device size is reduced, but dark current increases
Solution Approach 1:
The curved micro-pillar structures with diamond-shaped recesses featuring {111} crystallographic planes create optimized light paths that enhance photoelectron generation while the specific geometry helps suppress dark current by reducing surface recombination effects in the miniaturized structure.
3Reliability
If moth-eye structure is used to prevent light reflection, then sensitivity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the structural parameters by forming micro-pillars with specific height ratios (H/D = 0.5-2.0) and diamond-shaped recesses with {111} crystallographic planes, which can be achieved through standard photolithography and selective etching processes. This approach maintains manufacturing simplicity while achieving superior light trapping compared to conventional moth-eye structures.
Solution Approach 2:
The patent creates a composite micro-structure combining micro-pillars made of semiconductor material with diamond-shaped recesses filled with different materials or having different crystallographic orientations. This composite structure optimizes both light trapping performance and manufacturability through selective etching processes.
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 significantly improves quantum efficiency by reducing light reflection and increasing the diffraction of incident light, thereby enhancing the performance of BSI image sensors by increasing light path and suppressing dark current.
Implementation Method 1
a refractive index of the micro pillar gradually decreases from bottom to top and is smaller than a refractive index of the semiconductor material layer
Implementation Method 2
the micro pillar is provided with a refractive index gradually decreases from bottom to top... which may further reduce the reflection of incident light
Implementation Method 3
Each pixel includes a transistor, a capacitor and a photo-diode, wherein electrical energy is induced in the photo-diode upon exposure to the light. Each pixel generates electrons proportional to an amount of light falling on the pixel.
Data Source
AI summary
A method of fabricating a solid-state image sensor, including steps of forming a second type doped semiconductor layer and a semiconductor material layer sequentially on a first type doped semiconductor substrate to constitute a photoelectric conversion portion, forming a multilayer structure on the semiconductor material layer, wherein a refractive index of the multilayer structure gradually decreases from a bottom layer to a top layer of the multilayer structure and is smaller than a refractive index of the semiconductor material layer, and performing a photolithography process to the multiplayer structure and the photoelectric conversion portion to form multiple micro pillars, wherein the micro pillars protrude from the semiconductor material layer and are isolated by recesses extending into the photoelectric conversion portion.