Segmented Conductive EUV Mask Backside for Registration Correction

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Solution Overview

Problem

In extreme ultraviolet (EUV) lithography, correcting registration errors on reflection type photo masks is challenging due to the conductive layer covering the backside surface, which prevents laser irradiation used for error correction in conventional methods.

Innovation Solution

A blank mask design with a conductive layer exposed on the backside surface, either in trenches or as a checkerboard/mesh pattern, allowing laser irradiation for error correction, and including a laminated reflection layer and absorption layer on the front side, with optional capping and buffer layers, to facilitate accurate registration correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conductive layer covers the entire backside surface of the mask substrate, then the mask can be securely fixed on the electrostatic chuck, but laser irradiation for registration error correction becomes impossible

Engineering Contradiction:

Improvemask fixation stabilityVSAvoidregistration error correction capability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The conductive layer is segmented into a patterned structure (mesh, grid, or isolated regions) rather than forming a continuous film. This segmentation allows laser beams to pass through the gaps between conductive regions to irradiate the mask substrate for registration error correction, while still providing sufficient conductive areas to maintain electrostatic fixation stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the mask substrate are assigned different properties: areas with conductive layer material provide fixation functionality, while gaps or transparent regions provide laser transmission pathways. This local differentiation allows simultaneous achievement of both fixation stability and correction capability.

Inventive Principle:

Principle #3Local quality

2Ease of operation

If the conductive layer is made transparent to allow laser irradiation, then registration error correction becomes possible, but the electrostatic fixation capability may be reduced

Engineering Contradiction:

Improveregistration error correction capabilityVSAvoidmask fixation stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The conductive layer is divided into discrete patterned regions that are transparent or have reduced conductivity in certain areas, allowing laser penetration while maintaining sufficient conductive material distribution to ensure stable electrostatic fixation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The conductivity and transparency parameters of the conductive layer are optimized by controlling material composition, thickness, and pattern geometry. This allows tuning the layer to provide both adequate electrostatic fixation and sufficient laser transmission for registration correction.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a laminated reflection layer structure is used for EUV lithography, then EUV ray reflection efficiency is improved, but the mask structure complexity increases

Engineering Contradiction:

ImproveEUV ray reflection efficiencyVSAvoidmask structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The mask employs a laminated structure combining multiple materials (e.g., silicon oxide, molybdenum, silicon nitride) with different optical properties. This composite structure achieves high EUV reflection efficiency through constructive interference of reflected waves from multiple interfaces, while the layer thicknesses are optimized to maintain structural integrity without excessive complexity.

Inventive Principle:

Principle #40Composite materials

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

Enables reliable correction of registration errors in EUV lithography by allowing targeted laser irradiation through the conductive layer, improving overlay accuracy and mask registration precision.

Implementation Method 1

a reflection layer disposed on the first surface of the substrate to reflect extreme ultraviolet (EUV) rays

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

an absorption layer disposed on the reflection layer opposite to the substrate to absorb extreme ultraviolet (EUV) rays

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 3

the mask registration errors may be corrected by irradiating a laser onto a back side surface of a photo mask to deform a mask substrate

Methodology Applied

Scientific EffectLaser heating: Laser

Data Source

PatentUS8906582B2Blank masks for extreme ultra violet lithography, methods of fabricating the same, and methods of correcting registration errors thereof

Publication Date: 2014.12.09 MIMIRIP LLC

AI summary

Blank masks for extreme ultraviolet (EUV) photolithography are provided. The blank mask includes a substrate having a first surface and a second surface which are opposite to each other, a reflection layer disposed on the first surface of the substrate to reflect extreme ultraviolet (EUV) rays, an absorption layer disposed on the reflection layer opposite to the substrate to absorb extreme ultraviolet (EUV) rays, and a conductive layer disposed on the second surface of the substrate to expose portions of the substrate. Related methods are also provided.