Negatively Charged Layer Reduces Image Memory Effect

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Solution Overview

Problem

CMOS image sensors experience a 'memory effect' due to retained electrical signatures from high brightness images, leading to noise and blur in subsequent acquisitions, particularly exacerbated by advanced fabrication technologies like borderless contacts.

Innovation Solution

Incorporating a negatively charged layer between the contact etch stop layer and the pinning layer of the photodiode in CMOS image sensors to mask unwanted positive charges induced by strong light, reducing ghost artifacts and memory effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If advanced fabrication technologies with borderless contacts are used to maximize metal interconnect density, then productivity and device integration are improved, but memory effect and ghost artifacts are exacerbated

Engineering Contradiction:

Improvemetal interconnect densityVSAvoidmemory effect

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

A negatively charged layer is introduced as an intermediary between the contact etch stop layer and the pinning layer. This intermediate layer acts as a mediator that cancels out the harmful positive charges generated by borderless contacts during fabrication, thereby eliminating memory effects while preserving the high-density interconnect structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention converts the harmful positive charges generated by borderless contacts into a beneficial effect by introducing a negatively charged layer. The negative charges neutralize the unwanted positive charges, transforming the fabrication-induced defect into a controlled charge compensation mechanism that improves image quality

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If borderless contacts are implemented to increase metal interconnect density, then device complexity is reduced and manufacturing is simplified, but positive charges are induced in the contact etch stop layer causing ghost artifacts

Engineering Contradiction:

Improvecontact structure complexityVSAvoidpositive charges in contact etch stop layer

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The negatively charged layer serves as an intermediary that sits between the simplified borderless contact structure and the underlying layers. It compensates for the positive charges induced by the borderless contact fabrication process, allowing the use of simpler contact structures without suffering from charge-related artifacts

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the electrical parameter (charge state) of the contact etch stop layer interface by introducing fixed negative charges. This parameter change counteracts the unwanted positive charge accumulation, thereby eliminating the root cause of ghost artifacts while maintaining the borderless contact geometry

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If high brightness images are repeatedly exposed to the sensor, then signal strength is improved, but retained electrical signatures create noise and reduce signal-to-noise ratio in subsequent images

Engineering Contradiction:

Improvesignal strengthVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The negatively charged layer provides preliminary anti-action by pre-compensating for the positive charges that will be generated during high-brightness image exposure. This preemptive charge compensation prevents the formation of ghost artifacts before they can degrade subsequent image quality, allowing repeated high-signal exposures without accumulating noise

Inventive Principle:

Principle #9Preliminary anti-action

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 negatively charged layer effectively cancels out positive charges in the contact etch stop layer, significantly reducing or eliminating memory effects, thereby improving signal-to-noise ratio and image clarity.

Implementation Method 1

Incorporating a negatively charged layer between the contact etch stop layer and the pinning layer of the photodiode in CMOS image sensors to mask unwanted positive charges induced by strong light

Methodology Applied

Scientific EffectElectrostatic charge masking: Electrostatic Induction

Data Source

PatentUS9147776B2Negatively charged layer to reduce image memory effect

Publication Date: 2015.09.29 OMNIVISION TECHNOLOGIES INC

AI summary

An image sensor pixel includes a photodiode region having a first polarity doping type disposed in a semiconductor layer. A pinning surface layer having a second polarity doping type is disposed over the photodiode region in the semiconductor layer. The second polarity is opposite from the first polarity. A first polarity charge layer is disposed proximate to the pinning surface layer over the photodiode region. A contact etch stop layer is disposed over the photodiode region proximate to the first polarity charge layer. The first polarity charge layer is disposed between the pinning surface layer and the contact etch stop layer such that first polarity charge layer cancels out charge having a second polarity that is induced in the contact etch stop layer. A passivation layer is also disposed over the photodiode region between the pinning surface layer and the first polarity charge layer.