CMOS Image Sensor Composite Grid Crosstalk Reduction

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Solution Overview

Problem

Conventional BSI CMOS image sensors suffer from increased thickness due to the presence of a passivation layer, which also worsens optical crosstalk and reduces image quality.

Innovation Solution

A composite grid structure is formed by directly disposing a dielectric grid layer on a metal grid layer, with a conformal passivation layer covering the composite grid structure, reducing thickness and effectively blocking light diffusion to adjacent photoelectric devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a passivation layer is added to protect the metal grid, then the metal grid is protected from corrosion, but the sensor thickness increases and optical crosstalk worsens

Engineering Contradiction:

Improvemetal grid protectionVSAvoidsensor thickness

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent combines the passivation layer and color filter layer into a single integrated structure. The passivation layer is formed as part of the color filter stack, eliminating the need for a separate thick passivation layer while still providing corrosion protection to the metal grid.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent transitions from a planar passivation layer to a three-dimensional color filter structure that provides both protection and optical functionality. The color filters are formed with varying heights and depths, creating a multi-dimensional structure that accomplishes multiple functions simultaneously.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If a passivation layer is added to protect the metal grid, then the metal grid is protected from corrosion, but optical crosstalk increases

Engineering Contradiction:

Improvemetal grid protectionVSAvoidoptical crosstalk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The passivation function is merged with the color filter layer, which has inherent optical properties. The color filter structure provides both corrosion protection and optical isolation, preventing crosstalk between adjacent pixels while protecting the metal grid.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent applies different material compositions and structures at different locations within the color filter layer to optimize both protection and optical performance. The passivation layer is strategically positioned and configured to provide localized protection where needed while maintaining optical isolation.

Inventive Principle:

Principle #3Local quality

3Length of stationary object

If the sensor thickness is reduced, then the camera module can be thinner, but light sensitivity may decrease

Engineering Contradiction:

Improvesensor thicknessVSAvoidlight sensitivity

Core Design Contradiction:

Length of stationary objectVSUse of energy by moving object

Solution Approach 1:

The color filter layer performs multiple functions simultaneously: it provides optical filtering, passivation protection, and light guidance. This multi-functionality allows the sensor to maintain thin dimensions while preserving light sensitivity through optimized optical paths.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent optimizes various parameters including layer thicknesses, refractive indices, and geometric configurations to maximize light sensitivity in a thin structure. By carefully controlling these parameters, the sensor achieves high quantum efficiency despite reduced thickness.

Inventive Principle:

Principle #35Parameter changes

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 enhances quantum efficiency and image quality by shortening light paths and minimizing crosstalk, while maintaining a thinner sensor design.

Implementation Method 1

effectively blocking light diffusion to adjacent photoelectric devices

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 2

absorb light and convert the sensed light into digital data or electrical signals

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS9761622B2CMOS image sensor structure with crosstalk improvement

Publication Date: 2017.09.12 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device includes a substrate, a device layer, a composite grid structure, a passivation layer and color filters. The device layer overlies the substrate. The composite grid structure overlies the device layer. The composite grid structure includes cavities passing through the composite grid structure, and the composite grid structure includes a metal grid layer and a dielectric grid layer stacked on the metal grid layer. The passivation layer conformally covers the composite grid structure. The color filters respectively fill the cavities.