Multi-Layer Phase Shift Film for ArF Stray Light Control

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Solution Overview

Problem

The increasing complexity of illumination systems in semiconductor manufacturing leads to stray light issues due to multiple reflections in transfer masks, causing CD variations and making it difficult to achieve further miniaturization of transfer patterns, especially with ArF excimer laser exposure, where conventional phase shift masks struggle to maintain low back surface reflectance.

Innovation Solution

A phase shift mask blank with a stacked phase shift film structure on a transparent substrate, comprising layers with specific refractive indices, extinction coefficients, and film thicknesses, optimized to transmit ArF excimer laser light with a predetermined transmittance and generate a phase difference while reducing back surface reflectance to 9% or less, thereby suppressing stray light and CD variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a conventional phase shift mask is used with ArF excimer laser exposure, then pattern transmission is achieved, but back surface reflectance increases causing stray light and CD variations

Engineering Contradiction:

ImproveCD variation controlVSAvoidback surface reflectance

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The phase shift film is divided into multiple layers (first phase shift film layer, second phase shift film layer, and third phase shift film layer) with different refractive indices and thicknesses. This segmentation allows each layer to contribute differently to the overall optical performance, achieving low back surface reflectance while maintaining the required phase shift and light transmission characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses a composite multi-layer structure combining materials with different optical properties (different refractive indices and extinction coefficients). This composite approach enables simultaneous optimization of multiple parameters: phase shift generation, light transmission, and back surface reflectance suppression, which cannot be achieved with a single material.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If illumination system complexity increases to improve imaging, then imaging quality enhances, but stray light from multiple reflections increases

Engineering Contradiction:

Improveimaging qualityVSAvoidstray light

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potentially harmful multiple reflection effect into a beneficial one by designing the multi-layer phase shift film structure to create constructive interference for the desired imaging light while the reflections from each interface collectively reduce the back surface reflectance. The controlled reflections within the film stack become part of the solution rather than a problem.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Length of moving object

If wavelength is shortened from KrF to ArF excimer laser for miniaturization, then pattern resolution improves, but back surface reflectance control becomes more difficult

Engineering Contradiction:

Improvepattern sizeVSAvoidmask structure complexity

Core Design Contradiction:

Length of moving objectVSDevice complexity

Solution Approach 1:

The patent optimizes specific parameters of each layer including refractive index (n), extinction coefficient (k), and thickness (d) to achieve the desired optical performance at the shorter ArF wavelength (193 nm). By carefully controlling these parameters, the multi-layer structure achieves low back surface reflectance and appropriate phase shift while maintaining compatibility with the shorter wavelength exposure light.

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 effectively suppresses stray light and CD variations, enabling precise exposure transfer and achieving the desired pattern miniaturization by maintaining low back surface reflectance and ensuring high precision in semiconductor device manufacturing.

Implementation Method 1

the phase shift film has a function to transmit an exposure light of an ArF excimer laser at a predetermined transmittance and a function to generate a predetermined phase difference to the transmitting exposure light of an ArF excimer laser

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 2

refractive indexes n1 and n2 of the first layer and the second layer, respectively, at a wavelength of an exposure light of an ArF excimer laser satisfy a relation of n1<n2

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11442357B2Mask blank, phase-shift mask, and method of manufacturing semiconductor device

Publication Date: 2022.09.13 HOYA CORPORATION

AI summary

Provided is a mask blank, including a phase shift film. The phase shift film has a structure where a first layer and a second layer are stacked in this order from a side of the transparent substrate. The first layer is provided in contact with a surface of the transparent substrate. Refractive indexes n1 and n2 of the first layer and the second layer, respectively, at a wavelength of an exposure light of an ArF excimer laser satisfy the relation n1<n2. Extinction coefficients k1 and k2 of the first layer and the second layer, respectively, at a wavelength of the exposure light satisfy the relation k1<k2. Film thicknesses d1 and d2 of the first layer and the second layer, respectively, satisfy the relation d1<d2.