Backside Refraction Layer With Random Protrusions for Image Sensors

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Solution Overview

Problem

Backside illuminated CMOS image sensors face challenges in maximizing quantum efficiency due to the cost and complexity of manufacturing periodic refractive structures, which are necessary for effective photon absorption.

Innovation Solution

An anisotropic etch process is used to create a randomly refractive surface on the optical path within the image sensor, employing an etch chemistry that differentiates the etch rate between the masking material and the optically transparent material, resulting in a surface with random protrusions that enhance photon absorption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If periodic refractive structures are used to maximize quantum efficiency, then photon absorption is improved, but manufacturing cost and complexity increase

Engineering Contradiction:

Improvequantum efficiencyVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces symmetric periodic refractive structures with asymmetric random protrusions on the backside surface. These random protrusions have varying heights and lateral dimensions, creating asymmetric light scattering paths that effectively increase photon absorption probability without requiring precise periodic patterning, thereby reducing manufacturing complexity while maintaining quantum efficiency

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Instead of creating periodic structures through complex lithographic patterning on the backside, the patent inverts the approach by using anisotropic etching to create random protrusions. This inversion of the structure creation method simplifies the manufacturing process while achieving the same optical function of enhancing photon absorption through refractive effects

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If periodic refractive structures are used to maximize quantum efficiency, then photon absorption is improved, but manufacturing cost increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent employs a disposable masking layer that is easily applied and removed, replacing expensive lithographic patterning processes. The masking layer with random patterns is used during anisotropic etching to create the refractive structures, then discarded, significantly reducing manufacturing cost while maintaining the ability to create effective random protrusions for photon absorption

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent substitutes complex mechanical lithographic patterning systems with a simpler chemical etching process. By using anisotropic etching chemistry that selectively removes material based on crystal orientation, the patent creates random protrusions without requiring expensive lithography equipment, thereby reducing manufacturing cost while achieving the desired refractive structures

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 approach increases the quantum efficiency of the image sensor by randomly refracting photons, improving light absorption without the need for costly lithographic patterning of periodic structures.

Implementation Method 1

An other aspect provides a method of anisotropically etching a masking material layer to form a randomly refractive surface including random protrusions

Methodology Applied

Scientific EffectAnisotropic etching:

Implementation Method 2

an optically transparent layer having a second refractive index that is different from the first refractive index, thereby providing a refractive interface with the non-planar distal surface portions that refracts incident light in random directions

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS20240379704A1Backside refraction layer for backside illuminated image sensor and methods of forming the same

Publication Date: 2024.11.14 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Photosensors may be formed on a front side of a semiconductor substrate. An optical refraction layer having a first refractive index may be formed on a backside of the semiconductor substrate. A grid structure including openings is formed over the optical refraction layer. A masking material layer is formed over the grid structure and the optical refraction layer. The masking material layer may be anisotropically etched using an anisotropic etch process that collaterally etches a material of the optical refraction layer and forms non-planar distal surface portions including random protrusions on physically exposed portions of the optical refraction layer. An optically transparent layer having a second refractive index that is different from the first refractive index may be formed on the non-planar distal surface portions of the optical refraction layer. A refractive interface refracts incident light in random directions, and improves quantum efficiency of the photosensors.