Deep Trench Isolation Layout for CMOS Image Sensor Crosstalk

Solution Overview

Problem

CMOS image sensors face challenges in balancing lateral photon crosstalk and quantum efficiency, with metal BDTI structures reducing cross-talk but degrading quantum efficiency, and oxide BDTI structures improving quantum efficiency but increasing cross-talk.

Innovation Solution

A CMOS image sensor design incorporating a boundary deep trench isolation (BDTI) structure made of metal or polysilicon and a pixel deep trench isolation (PDTI) structure made of oxide, which reduces lateral photon crosstalk while maintaining high quantum efficiency by optimizing trench widths and depths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If metal BDTI structure is used, then lateral photon crosstalk is reduced, but quantum efficiency is degraded

Engineering Contradiction:

Improvelateral photon crosstalkVSAvoidquantum efficiency

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The isolation structure is divided into two distinct segments: BDTI (boundary deep trench isolation) made of metal for crosstalk reduction, and PDTI (pixel deep trench isolation) made of oxide for quantum efficiency maintenance. This segmentation allows each part to perform its specific function optimally without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different materials are assigned to different locations based on their specific functional requirements. Metal is used at the boundaries where crosstalk reduction is critical, while oxide is used within pixel regions where quantum efficiency is paramount. This local differentiation resolves the contradiction by optimizing material placement.

Inventive Principle:

Principle #3Local quality

2Reliability

If oxide BDTI structure is used, then quantum efficiency is improved, but lateral photon crosstalk increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidlateral photon crosstalk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The isolation structure is divided into two distinct segments: BDTI (boundary deep trench isolation) made of metal for crosstalk reduction, and PDTI (pixel deep trench isolation) made of oxide for quantum efficiency maintenance. This segmentation allows each part to perform its specific function optimally without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different materials are assigned to different locations based on their specific functional requirements. Metal is used at the boundaries where crosstalk reduction is critical, while oxide is used within pixel regions where quantum efficiency is paramount. This local differentiation resolves the contradiction by optimizing material placement.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If both BDTI and PDTI structures are made of the same material, then manufacturing is simplified, but cross-talk reduction and quantum efficiency cannot be optimized simultaneously

Engineering Contradiction:

Improvematerial uniformityVSAvoidcross-talk reduction and quantum efficiency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs a composite isolation structure combining two different materials: metal for BDTI and oxide for PDTI. This composite approach allows the system to achieve both crosstalk reduction and quantum efficiency optimization simultaneously, overcoming the limitations of using a single uniform material.

Inventive Principle:

Principle #40Composite materials

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 design achieves a good balance of reduced cross-talk and improved quantum efficiency, as demonstrated by higher quantum efficiency and lower cross-talk percentages compared to configurations with both structures made of the same material.

Implementation Method 1

A pixel region is surrounded by a boundary deep trench isolation (BDTI) structure laterally formed of metal or polysilicon and including a first set of BDTI segments extending in a first direction and a second set of BDTI segments extending in a second direction perpendicular to the first direction. Within the pixel region, a pixel deep trench isolation (PDTI) structure is formed of oxide and includes a first PDTI segment extending in the first direction and a second PDTI segment extending in the second direction.

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20240379714A1Deep trench isolation for cross-talk reduction

Publication Date: 2024.11.14 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Some embodiments relate to a CMOS image sensor disposed on a substrate. A plurality of pixel regions comprising a plurality of photodiodes, respectively, are configured to receive radiation that enters a back-side of the substrate. A boundary deep trench isolation (BDTI) structure is disposed at boundary regions of the pixel regions, and includes a first set of BDTI segments extending in a first direction and a second set of BDTI segments extending in a second direction perpendicular to the first direction to laterally surround the photodiode. The BDTI structure comprises a first material. A pixel deep trench isolation (PDTI) structure is disposed within the BDTI structure and overlies the photodiode. The PDTI structure comprises a second material that differs from the first material, and includes a first PDTI segment extending in the first direction such that the first PDTI segment is surrounded by the BDTI structure.