Chromeless Phase Shift Mask with Etch Stop Layer

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Solution Overview

Problem

Conventional chromeless phase shift masks face limitations in improving imaging quality and protecting the transparent substrate from damage during the manufacturing and usage processes, especially for sub-wavelength patterning where critical-dimension variations and high mask error factors are prevalent.

Innovation Solution

A chromeless phase shift mask structure incorporating an etch stop layer on a transparent substrate and a tunable transparent material layer with adjustable transmittance, designed to provide a 180° phase shift and enhanced imaging resolution, while the etch stop layer protects the substrate from damage during processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional chromeless phase shift mask is used, then the mask structure is simple, but the imaging quality is limited and the substrate lacks protection from damage

Engineering Contradiction:

Improvesubstrate protectionVSAvoidmask structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The mask structure is segmented into multiple functional layers: a transparent substrate, an etch stop layer for protection, and a tunable transparent material layer for phase shift control. This segmentation allows each layer to perform its specific function independently, improving substrate protection while maintaining imaging quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An etch stop layer is introduced as an intermediary protective layer between the transparent substrate and the tunable transparent material layer. This intermediary layer protects the substrate from damage during etching and processing while allowing optical transmission to proceed effectively.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the transparent material layer has fixed transmittance, then the manufacturing process is simple, but the freedom to improve imaging quality is limited

Engineering Contradiction:

Improvetransmittance tuning freedomVSAvoidmaterial composition

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The transmittance parameter of the transparent material layer is made tunable by varying the composition ratio of silicon oxide and silicon nitride. This allows continuous adjustment of transmittance to optimize imaging quality for different lithography conditions while maintaining a relatively simple two-material system.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The transparent material layer is formed as a composite of silicon oxide and silicon nitride materials. This composite structure enables independent control of optical properties (transmittance) and etch resistance, providing versatility in transmittance tuning while maintaining manufacturing feasibility.

Inventive Principle:

Principle #40Composite materials

3Strength

If no etch stop layer is used, then the mask structure is simpler, but the transparent substrate is vulnerable to damage during processing

Engineering Contradiction:

Improvesubstrate resistance to damageVSAvoidlayer structure

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

An etch stop layer is deposited beforehand on the transparent substrate to provide protective cushioning during subsequent etching processes. This layer prevents direct contact between etchants and the substrate, protecting the substrate from damage while enabling the formation of the tunable transparent material layer.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The etch stop layer acts as a disposable protective layer that is consumed during the etching process. It provides necessary protection during manufacturing but can be selectively removed or remains as a thin protective film, sacrificing a small amount of material to protect the valuable transparent substrate.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution enhances imaging quality and reduces substrate damage, leading to improved lithography performance with reduced best focus variation and increased freedom in transmittance tuning, thereby addressing the limitations of conventional masks.

Implementation Method 1

a circuit feature is defined in a transparent mask with phase shift between adjacent transparent regions such that destructive interference generates a dark feature

Methodology Applied

Scientific EffectPhase shift: Phase Change

Implementation Method 2

phase shift between adjacent transparent regions such that destructive interference generates a dark feature when imaged to a semiconductor substrate

Methodology Applied

Scientific EffectDestructive interference: Interference

Implementation Method 3

the etch stop layer protects the substrate from damage during processing

Methodology Applied

Scientific EffectPhysical barrier protection:

Data Source

PatentUS11022874B2Chromeless phase shift mask structure and process

Publication Date: 2021.06.01 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The present disclosure provides a mask. The mask includes a substrate; an etch stop layer disposed on the substrate, wherein the etch stop layer includes at least one of ruthenium oxide, tungsten nitride, and titanium nitride and is doped with at least one of phosphorous (P), calcium (Ca), and sodium (Na); and a material layer disposed on the etch stop layer and patterned to have an opening, wherein the etch stop layer completely covers a portion of the substrate within the opening.