Photon Blocking Layer for BSI Reference Pixel Noise

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Solution Overview

Problem

Back side illuminated (BSI) CMOS image sensors face interference from ambient photons that affect the accuracy of the reference pixel, leading to increased noise and reduced quantum efficiency and well capacity.

Innovation Solution

An extra film or spacer is disposed on the sidewall and edge of the reference pixel to block foreign photons, comprising materials like metal oxides and nitrides, forming a photon blocking layer that reduces dark current by preventing photon penetration into the semiconductor substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the reference pixel is made thinner to improve light sensing, then quantum efficiency is improved, but noise from ambient photons increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidnoise from ambient photons

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The device is divided into distinct functional regions: an image sensing region with photodiodes for light detection and a reference pixel region for noise reference. This segmentation allows the reference pixel to be specifically protected from ambient photons while the image sensing region maintains optimal light sensitivity through appropriate thickness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A photon blocking layer is introduced as an intermediary structure between the ambient environment and the reference pixel. This layer selectively blocks harmful photons from reaching the reference pixel while allowing the image sensing region to function normally, thereby reducing noise without compromising quantum efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the reference pixel region is enlarged to improve noise reference, then accuracy is improved, but interference from ambient environment increases

Engineering Contradiction:

Improveaccuracy of reference pixelVSAvoidinterference from ambient environment

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The device structure separates the reference pixel region from the image sensing region, with the reference pixel positioned in a peripheral area. This spatial segmentation allows the reference pixel to be enlarged for better noise reference capability while being physically isolated from the main light sensing area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The photon blocking layer acts as a protective intermediary that surrounds and shields the enlarged reference pixel region. This allows the reference pixel to be made larger for improved accuracy while the photon blocking layer prevents ambient photons from causing interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If a photon blocking layer is added to reduce dark current, then noise is reduced, but device complexity increases

Engineering Contradiction:

Improvedark currentVSAvoidstructure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The photon blocking layer is applied selectively only to the reference pixel region and peripheral areas, not to the entire device. This localized application reduces dark current and noise in the reference pixel while minimizing the increase in overall device complexity by avoiding unnecessary structures in the image sensing region.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The photon blocking layer is integrated with the existing device architecture using compatible materials and fabrication processes. The layer is formed as part of the device stack, combining multiple functions (noise blocking, structural support) in a single integrated structure rather than adding separate components.

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

The implementation of a photon blocking layer effectively reduces dark current and interference, enhancing the accuracy and performance of BSI image sensors by minimizing foreign photon intrusion.

Implementation Method 1

a photon blocking layer on a sidewall of the backside illumination semiconductor image sensing device. The photon blocking layer is configured to block photons penetrating into the semiconductor substrate

Methodology Applied

Scientific EffectPhoton blocking: Absorption (EM radiation)

Implementation Method 2

a first anti reflective coating on a backside of the semiconductor substrate

Methodology Applied

Scientific EffectAnti-reflection: Anti-Reflective Coating

Data Source

PatentUS10163972B2Image sensing device with photon blocking layer and anti-reflective coating

Publication Date: 2018.12.25 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of forming a semiconductor image sensing device includes: providing a semiconductor substrate; forming a radiation sensitive region and a peripheral region in the semiconductor substrate, wherein the peripheral region surrounds the radiation sensitive region and includes a top surface projected from a backside of the semiconductor substrate and a sidewall coplanar with a sidewall of the semiconductor substrate and perpendicular to the top surface; forming a photon blocking spacer in the peripheral region, wherein the photon blocking spacer covers a portion of the sidewall of the peripheral region; and forming an anti reflective coating adjacent to the photon blocking layer.