CMOS Image Sensor Contact Etch Stop Isolation

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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, especially in sensors with advanced fabrication technologies like borderless contacts, which exacerbate ghost artifacts.

Innovation Solution

Implementing a contact etch stop layer with isolation regions in CMOS image sensors to eliminate stress paths between photodiode regions and metal contacts, reducing the memory effect by isolating the metal contacts and the contact etch stop layer material from the photodiodes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If borderless contacts are used to maximize metal interconnect density, then metal interconnect density is improved, but memory effect and ghost artifacts are exacerbated

Engineering Contradiction:

Improvemetal interconnect densityVSAvoidmemory effect and ghost artifacts

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The contact etch stop layer is segmented into isolated regions rather than forming a continuous layer. These isolated contact etch stop regions are positioned beneath metal contacts but are spatially separated from photodiode regions, thereby maintaining metal interconnect density while eliminating stress paths that cause memory effect

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The contact etch stop layer material is removed from regions between metal contacts and photodiodes, extracting the harmful continuous stress path while preserving the necessary contact etch stop function beneath metal contacts. This selective removal eliminates charge trapping sites in the stress path region

Inventive Principle:

Principle #2Taking out (Extraction)

2Manufacturing precision

If advanced fabrication technologies are employed to maximize metal interconnect density, then manufacturing precision is improved, but ghost artifacts and memory effect increase

Engineering Contradiction:

Improvemetal interconnect densityVSAvoidghost artifacts

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The contact etch stop layer is divided into isolated regions that are precisely positioned using advanced fabrication techniques. This segmentation maintains the precision benefits of advanced fabrication while eliminating the continuous stress path that causes ghost artifacts

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS9287308B2Image sensor having metal contact coupled through a contact etch stop layer with an isolation region

Publication Date: 2016.03.15 OMNIVISION TECHNOLOGIES INC

AI summary

An image sensor pixel includes one or more photodiodes disposed in a semiconductor layer. Pixel circuitry is disposed in the semiconductor layer coupled to the one or more photodiodes. A passivation layer is disposed proximate to the semiconductor layer over the pixel circuitry and the one or more photodiodes. A contact etch stop layer is disposed over the passivation layer. One or more metal contacts are coupled to the pixel circuitry through the contact etch stop layer. One or more isolation regions are defined in the contact etch stop layer that isolate contact etch stop layer material through which the one or more metal contacts are coupled are coupled to the pixel circuitry from the one or more photodiodes.