Self-Aligned Deep Trench Isolation for Image Sensors

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Solution Overview

Problem

Existing back side illuminated (BSI) and front side illuminated (FSI) image sensor devices face issues with cross-talk and blooming due to insufficient isolation between neighboring pixels, which is exacerbated as transistor size shrinks, and conventional deep trench isolation (DTI) features are not sufficient to address these issues without compromising optical performance.

Innovation Solution

The method involves forming image sensor devices with self-aligned deep trench isolation (DTI) features, using a spacer layer as an etch-block along the sidewalls of shallow trench isolation (STI) features, allowing for a reduced critical dimension of both STI and DTI features, thereby enhancing optical performance without the need for an overlap margin.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional deep trench isolation (DTI) features are used to isolate neighboring pixels, then cross-talk and blooming issues are reduced, but the critical dimension increases which compromises optical performance

Engineering Contradiction:

Improveisolation between pixelsVSAvoidcritical dimension

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The isolation structure is divided into two segments: shallow trench isolation (STI) features formed first, followed by deep trench isolation (DTI) features formed using the STI features as alignment references. This segmentation allows each feature to be optimized independently while maintaining proper alignment

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The shallow trench isolation features are formed in advance before the deep trench isolation features. These preliminary STI features serve as alignment references that enable subsequent self-aligned formation of DTI features, eliminating the need for overlap margins

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If the critical dimension of STI and DTI features is reduced to improve optical performance, then quantum efficiency and dynamic range improve, but isolation between pixels becomes insufficient leading to cross-talk and blooming

Engineering Contradiction:

Improvecritical dimensionVSAvoidisolation between pixels

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The isolation approach transitions from relying solely on lateral critical dimension to utilizing vertical depth differentiation. DTI features extend deeper into the substrate than STI features, providing enhanced isolation in the vertical dimension while maintaining reduced lateral dimensions for optimal optical performance

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The shallow trench isolation features serve as intermediary structures that provide both optical optimization (through reduced critical dimension) and alignment reference functions. These intermediary STI features enable the formation of deeper DTI features without requiring increased lateral dimensions

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10170517B2Method for forming image sensor device

Publication Date: 2019.01.01 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method for forming an image sensor device on a substrate is disclosed. The method includes (a) recessing a portion of the substrate thereby forming a first shallow trench; (b) forming a spacer layer surrounding at least part of a sidewall of the first shallow trench; and (c) forming a first deep trench that extends below the first shallow trench by further recessing the substrate while using the spacer layer as a mask.