Backside Illuminated Sensor P+ Layer Optimization

Solution Overview

Problem

Backside illuminated imaging sensors face challenges with reduced sensitivity and increased crosstalk due to the absorption and recombination of blue light, which affects their performance in collecting visible light effectively.

Innovation Solution

A backside illuminated imaging sensor with a highly doped P+ layer, optimized ion concentration slope, and remaining substrate thickness is implemented to enhance quantum efficiency, reduce dark current, and minimize white pixel defects by carefully selecting the implant depth and ion concentration of the boron doped layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the semiconductor wafer thickness is increased to improve red light collection, then red light absorption is improved, but blue light photoelectrons recombine at the back surface leading to reduced sensitivity and increased crosstalk

Engineering Contradiction:

Improvered light collection efficiencyVSAvoidblue light sensitivity and crosstalk reduction

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent optimizes the semiconductor wafer thickness to a specific range (1.5-3.0 micrometers) to balance red light absorption and blue light photoelectron collection. This parameter optimization resolves the contradiction by finding the optimal thickness that allows sufficient red light penetration while preventing blue light photoelectron recombination at the back surface.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a back surface field (BSF) structure as an intermediary layer at the back surface of the semiconductor wafer. This BSF layer acts as a mediator that prevents photoelectron recombination at the back surface while maintaining transparent transmission for red light, thereby resolving the contradiction between red light collection and blue light sensitivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the semiconductor wafer thickness is decreased to reduce blue light photoelectron recombination, then blue light sensitivity is improved, but red light passes through without being absorbed reducing sensitivity

Engineering Contradiction:

Improveblue light sensitivity and crosstalk reductionVSAvoidred light absorption efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent optimizes the semiconductor wafer thickness to a specific range (1.5-3.0 micrometers) to balance red light absorption and blue light photoelectron collection. This parameter optimization resolves the contradiction by finding the optimal thickness that allows sufficient red light penetration while preventing blue light photoelectron recombination at the back surface.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a back surface field (BSF) structure as an intermediary layer at the back surface of the semiconductor wafer. This BSF layer acts as a mediator that prevents photoelectron recombination at the back surface while maintaining transparent transmission for red light, thereby resolving the contradiction between red light collection and blue light sensitivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Use of energy by moving object

If micro-lenses are added on the back surface to improve sensitivity, then light collection is improved, but device complexity increases

Engineering Contradiction:

Improvelight collection sensitivityVSAvoidsensor structure complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the need for complex micro-lens structures by optimizing the semiconductor wafer thickness and introducing a back surface field. This simplifies the device structure while maintaining improved light collection sensitivity through the optimized substrate thickness that naturally focuses light onto the photodiode region.

Inventive Principle:

Principle #2Taking out (Extraction)

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 solution significantly improves the sensitivity and spectral performance of the imaging sensor, reducing crosstalk and dark current while maintaining optimal substrate thickness for effective light collection across various wavelengths.

Implementation Method 1

blue light, which is absorbed near the surface, may generate photoelectrons that recombine at the back surface, return to the back surface or are collected at a neighboring pixel

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

A backside illuminated imaging sensor with backside P+ doped layer... optimized ion concentration slope... carefully selecting the implant depth and ion concentration of the boron doped layer

Methodology Applied

Scientific EffectElectric Field: Electric Field

Data Source

PatentEP2245666B1Backside illuminated imaging sensor with backside p+ doped layer

Publication Date: 2015.02.18 OMNIVISION TECHNOLOGIES INC

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Figure 3A~3F

AI summary

A backside illuminated imaging sensor includes a semiconductor layer having a P-type region. A frontside and backside P+ doped layers are formed within the semiconductor layer. An imaging pixel having a photodiode is formed within the semiconductor layer, where the photodiode is an N- region formed within the P-type region of the semiconductor layer between the frontside P+ doped layer and the backside P+ doped layer.