Embedded Microlens Fabrication for Image Sensors

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Solution Overview

Problem

Conventional microlens fabrication processes for semiconductor devices are limited by low temperature processing, requiring separate material and lithography processing, and non-standard packaging due to air gaps, which restricts device performance and scalability, especially in high-temperature applications and image resolution.

Innovation Solution

The method involves forming embedded microlenses with a truncated plano-convex shape using a dielectric film and isotropic etching, followed by deposition of high refractive index lens material, which eliminates the need for thermal curing and allows for integration in silicon wafer back-end-of-line processing, reducing the distance between the microlens and photo-sensing region for improved light focusing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional microlens fabrication process is used with separate material and lithography processing, then microlens can be formed on top of color filters, but the process complexity increases and requires non-standard packaging methods

Engineering Contradiction:

Improvemicrolens fabrication processVSAvoidprocessing steps

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent combines the microlens formation process with the color filter formation process into a single integrated process. The microlens material is deposited over the color filters in the same processing step, eliminating the need for separate material deposition and lithography steps. This merging of processes reduces overall complexity while maintaining the ability to form microlenses on top of color filters.

Inventive Principle:

Principle #5Merging (Combining)

2Ease of manufacture

If microlenses are formed at low temperature (about 200°C), then the process is simpler, but the microlenses cannot be used in high-temperature soldering applications

Engineering Contradiction:

Improveprocessing temperatureVSAvoidapplication temperature range

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent changes the material composition parameters of the microlens layer to enable high-temperature stability. By formulating the microlens material with heat-resistant components and adjusting the curing characteristics, the microlens can withstand high-temperature soldering processes (typically above 200°C) while maintaining its optical properties and structural integrity.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If air gap is introduced for facilitating proper focusing, then light focusing is improved, but non-standard packaging methods are required

Engineering Contradiction:

Improvelight focusing accuracyVSAvoidpackaging requirements

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts the air gap requirement from the packaging design by integrating the microlens formation directly into the color filter structure. The microlens material is deposited conformally over the color filters, creating the necessary optical path differences without requiring separate air gap structures or non-standard packaging approaches. This eliminates the need for specialized packaging while maintaining proper light focusing.

Inventive Principle:

Principle #2Taking out (Extraction)

4Manufacturing precision

If pixel size is decreased for achieving better image resolution, then image resolution improves, but the ability to make microlenses properly is limited

Engineering Contradiction:

Improveimage resolutionVSAvoidmicrolens fabrication

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent creates a universal microlens formation process that works across multiple pixel size generations. By using a conformal deposition approach and scalable material formulation, the same basic process can be applied to different pixel dimensions without requiring process redesign. This multi-functional approach allows the microlens fabrication to adapt to varying pixel sizes while maintaining proper microlens formation and optical performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 simplifies the microlens fabrication process, enhances image sensor performance by reducing oblique light issues, and allows for a wide range of lens materials suitable for high-temperature applications, increasing cost-effectiveness and scalability without the need for additional planarization steps.

Implementation Method 1

The method etches the dielectric film to form a cavity under the mask layer by introducing an isotropic etchant through the opening

Methodology Applied

Scientific EffectIsotropic etching:

Implementation Method 2

The second index of refraction is higher than the first index of refraction

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS8319303B2Method and system of embedded microlens

Publication Date: 2012.11.27 SEMICON MFG INT (SHANGHAI) CORP

AI summary

An image sensor includes an array of photo-sensing regions formed in a semiconductor substrate, a dielectric layer over the array of photo-sensing regions, and an array of microlenses formed in the dielectric layer. Each of the microlenses is center-aligned over one of the photo-sensing regions and has a truncated plano-convex shape. The microlenses have an index of refraction that is higher than the dielectric layer's refraction index. Each of the microlenses has a smooth circular top, a flat circular bottom, and a curved circumferential side convex towards the semiconductor substrate.