Floating Diffusion Doping Layout for CMOS Leakage and Blooming

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Solution Overview

Problem

Conventional image sensor manufacturing processes for CMOS image sensors require multiple photomasks and intermediary steps, leading to increased costs, time, and a higher likelihood of defects due to the formation of intermediary structures, which can affect the performance metrics such as floating diffusion leakage and blooming.

Innovation Solution

The use of a shared photomask to form a floating diffusion region with a central portion and a peripheral portion having different doping concentrations, allowing for precise control of dopant concentration and reduced likelihood of defects through angled ion implantation, thereby adjusting leakage and blooming characteristics without the need for intermediary structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If multiple photomasks are used for forming floating diffusion regions, then manufacturing precision can be maintained, but fabrication costs increase and defects increase

Engineering Contradiction:

Improvefloating diffusion region formation precisionVSAvoidfabrication cost and complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent combines multiple photomask functions into a single shared photomask. The photomask includes a first opening for the central portion and a second opening for the peripheral portion, allowing both regions to be patterned simultaneously in one lithography step, thereby eliminating the need for multiple separate photomasks and reducing fabrication complexity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The floating diffusion region is segmented into a central portion and a peripheral portion with different dopant concentrations. The shared photomask provides separate openings (first opening and second opening) that enable independent patterning control of each segment, allowing precise formation of both regions through a single photomask

Inventive Principle:

Principle #1Segmentation

2Ease of operation

If conventional photomask methods are used, then process simplicity is maintained, but control over dopant concentration and blooming characteristics is insufficient

Engineering Contradiction:

Improveprocess simplicityVSAvoiddopant concentration control

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The patent implements local quality by creating different dopant concentrations in different regions of the floating diffusion structure. The central portion receives a first dopant concentration while the peripheral portion receives a second dopant concentration, allowing localized optimization of electrical characteristics such as leakage control and blooming prevention

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If a single photomask is used for both central and peripheral portions, then fabrication costs reduce, but manufacturing precision may be compromised

Engineering Contradiction:

Improvefabrication cost reductionVSAvoidpattern formation precision

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The shared photomask is segmented with distinct first and second openings positioned at different locations. The first opening aligns with the central portion while the second opening aligns with the peripheral portion, enabling precise independent patterning of each region through a single photomask without compromising manufacturing precision

Inventive Principle:

Principle #1Segmentation

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

This approach reduces manufacturing costs and defects while enhancing the performance metrics of CMOS image sensors by allowing precise control over the floating diffusion region, improving leakage and blooming characteristics.

Implementation Method 1

implanting first dopants to form a central portion of the floating diffusion region

Methodology Applied

Scientific EffectIon Implantation: Ion Implantation

Data Source

PatentUS20240194719A1Floating diffusion region formed via shared photomask and methods thereof

Publication Date: 2024.06.13 OMNIVISION TECHNOLOGIES INC

AI summary

An image sensor including a plurality of photodiodes disposed within a semiconductor substrate proximate to a first side of the semiconductor substrate, a first transfer gate and a second transfer gate that are each disposed proximate to the first side of the semiconductor substrate and coupled to a respective one of the plurality of photodiodes, and a floating diffusion region coupled to the first transfer gate and the second transfer gate is described. The first transfer gate is laterally separated from the second transfer gate by a separation distance. The floating diffusion region extends laterally within the semiconductor substrate a distance greater than the separation distance between the first transfer gate and the second transfer gate. The floating diffusion region includes a central portion surrounded by a peripheral portion. A first dopant concentration of the central portion is greater than a second dopant concentration of the peripheral portion.