Triple-Dielectric ARC Structure for Higher Image Sensor Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors face challenges with reflection of incident radiation away from underlying image sensor elements due to insufficient bending of light by the anti-reflective coating (ARC) structure, leading to decreased quantum efficiency and increased cross-talk, which affects overall performance.
Innovation Solution
The ARC structure is enhanced by using a combination of three dielectric layers with specific refractive indices, where the second index is greater than the first and the third is less than the first, effectively directing incident light towards the image sensor element and reducing reflection and cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer anti-reflective coating is used, then the device complexity is reduced, but the quantum efficiency decreases due to insufficient light bending and increased reflection
Solution Approach 1:
The anti-reflective coating is divided into three separate dielectric layers with different refractive indices instead of using a single-layer coating. This segmentation allows each layer to contribute differently to light bending, achieving superior quantum efficiency through cumulative refraction effects while maintaining manageable structural complexity.
Solution Approach 2:
The patent employs a composite structure consisting of three dielectric layers with progressively lower refractive indices (first layer: highest index, second layer: intermediate index, third layer: lowest index). This composite material approach enables optimized light management by combining materials with complementary optical properties to achieve enhanced light bending and reduced reflection.
2Ease of manufacture
If the ARC structure uses materials with similar refractive indices, then the ease of manufacture is improved, but the light bending capability decreases leading to increased cross-talk
Solution Approach 1:
Each dielectric layer is assigned a specific refractive index tailored to its position in the stack, creating local optical quality variations. The first layer has the highest refractive index for initial light capture, the second layer has an intermediate index for continued bending, and the third layer has the lowest index for final direction control. This localized optimization of material properties maximizes light bending capability while preventing cross-talk.
3Productivity
If the ARC structure is simplified to reduce device complexity, then the manufacturing cost decreases, but the quantum efficiency and performance are compromised
Solution Approach 1:
The patent optimizes specific parameters including the refractive index values of each dielectric layer, their respective thicknesses, and their stacking sequence. By carefully controlling these parameters, the three-layer structure achieves enhanced quantum efficiency and reduced cross-talk while remaining compatible with standard semiconductor manufacturing processes, thus maintaining manufacturing productivity.
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 increases the quantum efficiency of the pixel sensor by ensuring incident light is directed towards the image sensor element, thereby enhancing the overall performance by mitigating reflection and cross-talk.
Implementation Method 1
The first dielectric layer has a first index of refraction that is greater than a second index of refraction of the second dielectric layer such that a difference between the first and second indices of refraction is relatively small (e.g., less than about 0.6), and incident light that passes from the second dielectric layer to the first dielectric layer is bent towards a line that is normal to an upper surface of the first dielectric layer
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a pixel sensor. The pixel sensor includes a substrate having a front-side opposite a back-side. An image sensor element comprises an active layer disposed within the substrate, where the active layer comprises germanium. An anti-reflective coating (ARC) structure overlies the back-side of the substrate. The ARC structure includes a first dielectric layer overlying the back-side of the substrate, a second dielectric layer overlying the first dielectric layer, and a third dielectric layer overlying the second dielectric layer. A first index of refraction of the first dielectric layer is less than a second index of refraction of the second dielectric layer, and a third index of refraction of the third dielectric layer is less than the first index of refraction.