Image Sensor Deep Trench Isolation for Striation-Free Color Filter

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Solution Overview

Problem

Conventional CMOS image sensor manufacturing processes suffer from striation issues due to the color filter array being formed on a dielectric layer after an opening is created, leading to non-uniform thickness and adverse effects on pixel performance.

Innovation Solution

The method involves forming a bonding pad on the back side of the substrate with parts of the substrate between the bonding pad and the first metal layer, preventing the color filter layer from being stored in openings during spin coating, and using deep trench isolation to shield the bonding pad and connecting elements, thus avoiding striation and improving pixel performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If an opening is formed to expose the metal trace for bonding pad formation, then the bonding pad can be formed to connect other components, but the color filter layer is stored up in the opening during spin coating, causing non-uniform thickness and striation

Engineering Contradiction:

Improvebonding pad formationVSAvoidcolor filter layer uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The deep trench isolation structure is formed preliminarily before bonding pad formation to prevent the color filter layer from being stored in openings during subsequent spin coating processes. This preliminary structural preparation eliminates the root cause of striation while maintaining bonding pad functionality.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The substrate is segmented into distinct regions: the sensor array region with photodiodes, the peripheral region with bonding pads, and the deep trench isolation structures separating these regions. This segmentation allows independent optimization of each region's function while preventing interference between them.

Inventive Principle:

Principle #1Segmentation

2Productivity

If the color filter array is formed on the dielectric layer through spin coating after the opening is completed, then the manufacturing process can proceed, but the color filter layer thickness becomes non-uniform due to storage and spinning out from the opening

Engineering Contradiction:

Improvemanufacturing process continuityVSAvoidcolor filter layer thickness uniformity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The problematic opening structure is extracted and replaced with a deep trench isolation structure that extends through the substrate. This extraction removes the source of color filter layer distortion while maintaining the necessary electrical connections through the substrate.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The deep trench isolation structure acts as an intermediary element between the bonding pad region and the sensor array region. It provides mechanical support and electrical isolation, preventing the color filter layer from being disturbed during spin coating while allowing the manufacturing process to continue smoothly.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the bonding pad is formed with an opening to expose the metal trace, then electrical connection can be established, but striation occurs that adversely affects pixel performance

Engineering Contradiction:

Improveelectrical connectionVSAvoidstriation affecting pixel performance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The connection structure is extended into the depth dimension by forming deep trench isolation structures that penetrate through the substrate. This dimensional extension provides both electrical connection pathways and physical barriers that prevent surface-level striation from affecting pixel performance.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Different regions of the substrate are given different local qualities: the bonding pad region has conductive properties for electrical connection, while the deep trench isolation regions provide insulating properties to prevent current leakage and striation formation. This localized differentiation resolves the contradiction between connection reliability and pixel performance.

Inventive Principle:

Principle #3Local quality

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 prevents striation and enhances the uniformity of the color filter layer, leading to improved pixel performance and saturation in CMOS image sensors by eliminating the formation of recesses during spin coating.

Implementation Method 1

the color filter array 36 is formed on the dielectric layer 12 through a spin coating process

Methodology Applied

Scientific EffectSpin coating: Spin Coating

Data Source

PatentUS8779344B2Image sensor including a deep trench isolation (DTI)that does not contact a connecting element physically

Publication Date: 2014.07.15 UNITED MICROELECTRONICS CORP

AI summary

An image sensor includes a substrate with a front side and a back side, the substrate having a sensor array region and a peripheral region defined thereon, a plurality of sensor device disposed in the sensor array region, a first metal layer disposed on the front sides within the peripheral region, a bonding pad disposed on the backside within the peripheral region, and at least a connecting element penetrating the substrate and substantially connect to the first metal layer and the bonding pad, wherein parts of the substrate is between the bonding pad and the first metal layer.