CMOS Image Sensor LTO Layer Removal and Microlens Protection

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Solution Overview

Problem

The existing manufacturing methods for CMOS image sensors face issues such as peeling and crack phenomena of the low temperature oxide (LTO) layer, which can damage microlenses and increase the optical path length to the photodiode, and also lead to particle attachment during the wafer sawing process.

Innovation Solution

The method involves forming an image sensor without an LTO layer, using a titanium tungsten layer as an adhesive layer and a gold bump to connect the pad, and thinly depositing an LTO layer over the microlenses to prevent damage and particle attachment, with the LTO layer being selectively removed using a fluoric acid-based vapor etching process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an LTO layer is formed over the microlenses to protect them during manufacturing, then microlens damage is prevented, but the LTO layer causes peeling and crack phenomena that damage the microlenses

Engineering Contradiction:

Improvemicrolens protectionVSAvoidpeeling and crack phenomena

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent removes the LTO layer completely from the manufacturing process. Instead of forming an LTO layer over the microlenses, the invention uses alternative protective measures such as forming a protective film over the color filter and using a specific sequence of forming the microlenses after other layers are in place, thereby eliminating the peeling and crack issues while still protecting the microlenses

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent forms a protective film over the color filter before forming the microlenses. This preliminary protective layer is in place before the microlenses are created, providing protection during subsequent manufacturing steps without causing the peeling and crack problems that occur when LTO is formed after the microlenses

Inventive Principle:

Principle #10Preliminary action

2Reliability

If an LTO layer is formed over the microlenses, then protection during manufacturing is provided, but the optical path length to the photodiode increases

Engineering Contradiction:

Improvemicrolens protectionVSAvoidoptical path length

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent eliminates the LTO layer entirely from the structure. By not forming the LTO layer over the microlenses, the optical path from the microlens to the photodiode remains short and direct, improving optical performance while still providing necessary protection through alternative methods such as the protective film formed over the color filter

Inventive Principle:

Principle #2Taking out (Extraction)

3Productivity

If wafer sawing is performed without protective measures, then manufacturing efficiency is maintained, but particle attachment occurs on the microlenses

Engineering Contradiction:

Improvemanufacturing efficiencyVSAvoidparticle attachment

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent forms a protective film over the color filter and structures before the wafer sawing process. This preliminary protective layer prevents particle attachment during sawing while allowing the process to proceed efficiently. The protective film acts as a barrier that can be removed or integrated into the final structure without compromising manufacturing productivity

Inventive Principle:

Principle #10Preliminary 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

This approach prevents peeling and crack phenomena, minimizes optical path length, and avoids microlens damage and particle attachment, enabling more efficient manufacturing of CMOS image sensors with improved performance.

Implementation Method 1

the LTO layer being selectively removed using a fluoric acid-based vapor etching process

Methodology Applied

Scientific EffectChemical etching: Chemical Vapour Deposition

Data Source

PatentUS8222069B2Image sensor and manufacturing method for same

Publication Date: 2012.07.17 INTELLECTUAL VENTURES II LLC

AI summary

An image sensor including a first region where a pad is to be formed, and a second region where a light-receiving element is to be formed. A pad is formed over a substrate of the first region. A passivation layer is formed over the substrate of the first and second regions to expose a portion of the pad. A color filter is formed over the passivation layer of the second region. A microlens is formed over the color filter. A bump is formed over the pad. A protective layer is formed between the bump and the pad to expose the portion of the pad.