Photomask Cooling Layer for Electron Beam Heat Dissipation

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Solution Overview

Problem

In photolithography, as IC dimensions decrease and density increases, achieving precise pattern transfer with current resolution enhancement techniques like OPC, OAI, DDL, and PSM is challenging due to issues with depth of focus and critical dimension control, particularly with high current density electron beam exposure causing proximity scattering and resist heating effects.

Innovation Solution

A mask blank structure comprising a transparent substrate, an opaque layer, a cooling layer with thermal conductivity of 160≤k≤5000 and effective atomic number of 5≤Zeff≤14, and a resist layer, where the cooling layer is positioned between the opaque and resist layers to control electron scattering and dissipate heat, improving patterning precision and uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high current density electron beam exposure is used to improve productivity, then patterning speed increases, but proximity scattering and resist heating effects worsen, degrading manufacturing precision

Engineering Contradiction:

Improvepatterning speedVSAvoidcritical dimension control

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

A cooling layer comprising a first cooling layer and a second cooling layer is introduced as an intermediary between the resist layer and the substrate. The first cooling layer is in direct contact with the resist layer, while the second cooling layer contacts the substrate. This cooling layer structure acts as a thermal mediator that conducts heat away from the resist layer during high current density electron beam exposure, thereby reducing resist heating effects and improving critical dimension control while maintaining high patterning speed

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the thermal parameters of the mask blank structure by introducing materials with high thermal conductivity (greater than 100 W/mK) in the cooling layer. This parameter change enables efficient heat dissipation from the resist layer during electron beam exposure, allowing high current density operation without the detrimental heating effects that would otherwise degrade critical dimension control

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If resolution enhancement techniques are applied to improve manufacturing precision, then critical dimension control improves, but device complexity increases

Engineering Contradiction:

Improvecritical dimension controlVSAvoidmask blank structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The cooling layer is selectively positioned only in regions where heat dissipation is critical - specifically, the first cooling layer contacts the resist layer in the patterned regions, while the second cooling layer contacts the substrate. This local quality approach provides targeted thermal management where needed without adding unnecessary complexity to the entire mask blank structure

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The mask blank structure is designed as a composite with multiple functional layers: the cooling layer uses materials with high thermal conductivity (greater than 100 W/mK) to conduct heat away, while the substrate provides mechanical support and electrical properties. This composite structure achieves effective heat dissipation for improved critical dimension control while maintaining overall structural integrity

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

The cooling layer enhances critical dimension control and uniformity by reducing electron scattering angles and preventing resist deformation, achieving improved pattern transfer with a 10-50% improvement in critical dimension precision.

Implementation Method 1

a cooling layer disposed on the opaque layer, wherein the cooling layer has a thermal conductivity of 160≤k≤5000

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

controlling electron scattering and dissipating heat

Methodology Applied

Scientific EffectElectron scattering: Scattering

Data Source

PatentUS10459332B2Mask blank and fabrication method thereof, and method of fabricating photomask

Publication Date: 2019.10.29 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of fabricating a photomask includes providing a mask blank; removing a portion of the resist layer to form a patterned resist layer exposing a portion of the cooling layer; patterning the cooling layer by using the patterned resist layer as an etching mask; patterning the opaque layer; and removing the patterned resist layer and the patterned cooling layer. The mask blank includes a light-transmitting substrate and an opaque layer, a cooling layer, and a resist layer sequentially stacked thereon, wherein the cooling layer has a thermal conductivity ranging between 160 and 5000 and an effective atomic number ranging between 5 and 14.