Alignment Mark Structure for MRAM CMP Protection

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Solution Overview

Problem

In the production of semiconductor components, alignment marks are often obscured by opaque materials like magnetic layers in MRAM devices, making precise alignment challenging, and are also vulnerable to damage during chemical mechanical polishing (CMP) processes.

Innovation Solution

A novel alignment mark structure is created with a trench embedded in a dielectric layer, filled with a metal layer and covered by multiple material layers (silicon nitride, silicon oxide, tantalum-containing, aluminum-containing, or low-k dielectric) with specific reflectance properties, allowing for precise alignment and protection from CMP.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If opaque magnetic layers are used in MRAM devices, then data storage capability is improved, but alignment mark visibility deteriorates

Engineering Contradiction:

Improvedata storage capabilityVSAvoidalignment mark visibility

Core Design Contradiction:

Quantity of substanceVSDifficulty of detecting and measuring

Solution Approach 1:

The alignment mark structure is segmented into multiple functional layers: a reflective metal layer at the bottom for optical contrast, a dielectric layer in the middle for protection and isolation, and a top material layer for CMP protection. This segmentation allows the alignment mark to maintain visibility through opaque magnetic layers while protecting against manufacturing processes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dielectric layer is introduced as an intermediary between the metal alignment mark and the opaque magnetic layers. This dielectric layer allows optical signals to pass through while providing physical protection, serving as a mediator that resolves the conflict between visibility and protection requirements.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If alignment marks are placed on wafer surface, then alignment function is improved, but vulnerability to CMP damage increases

Engineering Contradiction:

Improvealignment functionVSAvoidCMP damage vulnerability

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The alignment mark structure incorporates a protective dielectric layer and top material layer before the CMP process is applied to the wafer. These layers act as a cushion that protects the underlying metal alignment mark from CMP damage, allowing the alignment function to be preserved while withstanding the harmful CMP process.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The alignment mark is constructed as a composite structure combining metal (for reflectivity and alignment function), dielectric material (for protection and isolation), and top coat material (for CMP resistance). This composite material approach allows simultaneous achievement of alignment functionality and CMP protection.

Inventive Principle:

Principle #40Composite materials

3Illumination intensity

If metal layers are used for alignment marks, then optical contrast is improved, but protection from CMP processes deteriorates

Engineering Contradiction:

Improveoptical contrastVSAvoidCMP process resistance

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The alignment mark structure segments the metal layer from the CMP process by introducing dielectric and top material layers. The metal layer maintains optical contrast while the overlying protective layers absorb CMP damage, resolving the contradiction between metal's optical benefits and CMP vulnerability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Dielectric and top material layers are introduced as intermediaries between the metal alignment mark and the CMP process. These intermediary layers allow the metal to maintain high optical contrast while being protected from CMP damage, mediating between optical performance and manufacturing robustness.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The alignment mark structure provides enhanced optical contrast, enabling precise alignment of opaque materials and withstanding CMP processes, thereby improving the accuracy and reliability of semiconductor manufacturing.

Implementation Method 1

a reflectance of the first material layer is larger than a reflectance of the second material layer, the reflectance of the second material layer is larger than a reflectance of the third material layer

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11145602B2Alignment mark structure and method of fabricating the same

Publication Date: 2021.10.12 UNITED MICROELECTRONICS CORP

AI summary

An alignment mark structure includes a dielectric layer. A trench is embedded in the dielectric layer. An alignment mark fills up the trench, wherein the alignment mark includes a metal layer covering the trench. A first material layer covers and contacts the metal layer. A second material layer covers and contacts the first material layer. A third material layer covers and contacts the second material layer. The first material layer, the second material layer, and the third material layer independently includes silicon nitride, silicon oxide, tantalum-containing material, aluminum-containing material, titanium-containing material, or a low-k dielectric having a dielectric constant smaller than 2.7, and a reflectance of the first material layer is larger than a reflectance of the second material layer, the reflectance of the second material layer is larger than a reflectance of the third material layer.