BSI Image Sensor Surface Grooves for Higher Quantum Efficiency

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Solution Overview

Problem

Backside illuminated (BSI) image sensors face reduced quantum efficiency due to light reflection from the planarized silicon surface, which diminishes the absorption of incident light in the radiation-sensing region.

Innovation Solution

The implementation of a modified surface topography with a periodic groove pattern increases the effective surface area for light absorption without increasing device dimensions. This surface modification also provides an equivalent gradient refractive index (GRIN) material, reducing reflections and enhancing light input efficiency. Additionally, a backside deep trench isolation (BDTI) structure with increased depth is embedded in a thick silicon layer to improve device isolation and reduce crosstalk.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a planarized silicon surface is used in BSI image sensors, then device manufacturing is simplified, but light reflection increases and quantum efficiency decreases

Engineering Contradiction:

Improvesurface planarization processVSAvoidquantum efficiency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies curvature by replacing the planar silicon surface with a microlens array structure having a curved, dome-shaped surface. Each microlens is formed with a specific radius of curvature to focus incident light onto the underlying photodiode, thereby reducing reflection and improving light absorption while maintaining manufacturing feasibility through standard semiconductor processing techniques

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the surface geometry parameter from flat to curved by forming microlenses with controlled radii (e.g., 0.5-2.0 micrometers). This parameter change transforms the optical properties of the surface, reducing Fresnel reflection and increasing light coupling efficiency into the photodetector, thus improving quantum efficiency without complicating the manufacturing process

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the silicon layer thickness is increased to improve light absorption, then quantum efficiency improves, but device dimensions increase

Engineering Contradiction:

Improvelight absorption efficiencyVSAvoidsilicon layer thickness

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The microlens curvature concentrates incident light rays onto a smaller focal area on the photodiode, effectively increasing the light absorption probability in a thinner silicon layer. The curved surface acts as an optical concentrator, allowing adequate light absorption without increasing the overall device thickness

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent addresses the light absorption problem by transitioning from a one-dimensional solution (increasing thickness) to a two-dimensional solution (adding surface curvature through microlenses). The microlens array provides optical focusing in the vertical dimension while maintaining a compact overall device structure

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If a periodic groove pattern is etched on the silicon surface to reduce reflection, then quantum efficiency improves, but manufacturing complexity increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidsurface structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a curved microlens surface that can be formed using standard semiconductor fabrication techniques such as spin-coating photoresist and reflow processing. This curved surface structure reduces reflection through geometric optics principles while maintaining compatibility with existing manufacturing processes, avoiding the need for complex groove patterning

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 modified surface topography and BDTI structure significantly improve the quantum efficiency of BSI image sensors by increasing light absorption and reducing reflections, while also enhancing device isolation and reducing crosstalk.

Implementation Method 1

increases the effective surface area for light absorption

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 2

provides an equivalent gradient refractive index (GRIN) material, reducing reflections

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

improve device isolation and reduce crosstalk

Methodology Applied

Scientific EffectElectrical isolation: Physical Containment

Data Source

PatentUS12324258B2Image sensor with improved quantum efficiency surface structure

Publication Date: 2025.06.03 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The present disclosure relates to a semiconductor image sensor with improved quantum efficiency. The semiconductor image sensor can include a semiconductor layer having a first surface and a second surface opposite of the first surface. An interconnect structure is disposed on the first surface of the semiconductor layer, and radiation-sensing regions are formed in the semiconductor layer. The radiation-sensing regions are configured to sense radiation that enters the semiconductor layer from the second surface and groove structures are formed on the second surface of the semiconductor layer.