Reflective EUV Photomask Blank with Ru-Si Capping Layer

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Solution Overview

Problem

Reflective EUV photomasks face challenges with contamination and physical damage due to high energy EUV rays, leading to reduced lifetimes and reflectivity degradation, especially when employing cleaning processes.

Innovation Solution

A reflective photomask blank with a multi-layered reflection layer, a capping layer containing transition metals like ruthenium and silicon, and a passivation layer to prevent oxygen introduction, along with a light absorption layer, is used to enhance durability and prevent oxidation at the interface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If reflective EUV photomasks are used in exposure processes, then pattern transfer capability is improved, but contamination and physical damage occur leading to reduced lifetime

Engineering Contradiction:

Improvepattern transfer capabilityVSAvoidphotomask lifetime

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent employs a multi-layer composite structure consisting of a reflective layer (molybdenum/silicon alternated layers), a capping layer (ruthenium and silicon), and a passivation layer (silicon oxide). This composite material approach protects the reflective layer from EUV-induced contamination and oxidation, thereby extending photomask lifetime while maintaining pattern transfer capability

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The capping layer containing ruthenium and silicon creates a protective barrier that establishes an inert environment for the reflective layer, preventing oxygen and contaminant ingress during the exposure process. This inert protective environment reduces oxidation and contamination, improving photomask reliability

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

2Object-generated harmful factors

If cleaning processes are applied to remove contamination, then reflectivity is temporarily restored, but physical damage and oxidation occur reducing overall durability

Engineering Contradiction:

Improvecontamination removalVSAvoidphotomask durability

Core Design Contradiction:

Object-generated harmful factorsVSStrength

Solution Approach 1:

The passivation layer (silicon oxide) and capping layer are deposited beforehand to cushion and protect the reflective layer from oxidation and physical damage during cleaning processes. This pre-protective barrier allows cleaning to proceed with minimal damage to the underlying reflective structure

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The passivation layer creates a chemically inert barrier that prevents oxygen from reaching the reflective layer during cleaning processes. This inert protection prevents oxidation that would otherwise occur during exposure to cleaning chemicals and atmospheric oxygen

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

3Reliability

If capping layer with transition metal and silicon is used, then oxidation at interface is prevented, but manufacturing complexity increases

Engineering Contradiction:

Improveinterface oxidation preventionVSAvoidlayer structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The capping layer uses specific compositional parameters (ruthenium and silicon content ratios) and thickness parameters to achieve optimal oxidation prevention. By carefully controlling these parameters, the patent achieves effective protection without excessive complexity in the layer structure

Inventive Principle:

Principle #35Parameter changes

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 extends the lifespan of reflective photomasks by preventing oxidation and physical damage, maintaining reflectivity even after repeated exposure and cleaning processes.

Implementation Method 1

a passivation layer disposed on a surface of the capping layer opposite to the multi-layered reflection layer and configured to prevent oxygen atoms from being introduced into an interface between the multi-layered reflection layer and the capping layer

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Implementation Method 2

The EUV lithography process may be performed using a reflective exposure system including reflective EUV photomasks to transfer patterns of each reflective EUV photomask onto a wafer

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

a light absorption layer on the passivation layer

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Data Source

PatentUS9454074B2Reflective photomask blanks and reflective photomasks

Publication Date: 2016.09.27 SAMSUNG ELECTRONICS CO LTD

AI summary

Reflective photomask blanks are provided. The reflective photomask blank includes a multi-layered reflection layer on a photomask substrate, a capping layer directly disposed on a top surface of the multi-layered reflection layer to include transition metal and silicon, a passivation layer disposed on a surface of the capping layer opposite to the multi-layered reflection layer, and a light absorption layer on the passivation layer.