Photomask Blank Dual-Layer Etching Precision

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Solution Overview

Problem

Conventional photomask blank structures fail to achieve highly precise formation of fine photomask patterns due to the burden on the photoresist during etching, particularly with exposure light having short wavelengths, leading to issues like pattern degradation and reduced transfer accuracy.

Innovation Solution

A photomask blank with a light-shielding film comprising a chromium-based first layer and a silicon-containing second layer, where the second layer is etched using fluorine-based dry etching, allowing the first layer to be patterned with reduced photoresist burden and maintaining high precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single-layer chromium-based light-shielding film is used, then the light-shielding performance is sufficient, but the etching process causes excessive burden on the photoresist leading to pattern degradation

Engineering Contradiction:

Improvelight-shielding performanceVSAvoidpattern transfer accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The light-shielding film is divided into two distinct layers: a chromium-based first layer for light-shielding and a silicon-containing second layer for etching. This segmentation allows each layer to perform its specific function optimally without interfering with the photoresist, thereby maintaining pattern transfer accuracy while ensuring adequate light-shielding performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The silicon-containing second layer acts as an intermediary between the chromium-based first layer and the photoresist. This intermediate layer can be etched selectively without damaging the photoresist, serving as a protective barrier that enables precise pattern transfer while allowing the chromium layer to provide necessary light-shielding properties.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If the photoresist thickness is reduced to minimize aspect ratio, then the pattern precision is improved, but the etching resistance decreases making the photoresist more susceptible to damage

Engineering Contradiction:

Improvepattern precisionVSAvoidetching resistance

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The silicon-containing second layer serves as a protective intermediary that shields the thin photoresist from direct exposure to harsh etching conditions. This allows the photoresist to be made thinner for better pattern precision while the intermediate layer provides the necessary etching resistance, effectively decoupling the trade-off between thickness and resistance.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The chromium-based first layer acts as a protective copy or replica that preserves the pattern information while the silicon-containing second layer handles the actual etching process. This separation allows the photoresist to maintain thinness for precision while the chromium layer provides structural support and protection during etching.

Inventive Principle:

Principle #26Copying

3Device complexity

If conventional single-layer light-shielding film is used, then the structure is simple, but the photoresist burden during etching cannot be reduced

Engineering Contradiction:

Improvefilm structure complexityVSAvoidphotoresist processing ease

Core Design Contradiction:

Device complexityVSEase of manufacture

Solution Approach 1:

The light-shielding film structure is segmented into two functional layers with distinct roles: the chromium-based first layer provides light-shielding properties while the silicon-containing second layer is optimized for etching. This segmentation, while increasing structural complexity, dramatically improves ease of manufacture by reducing photoresist burden and enabling more reliable pattern transfer.

Inventive Principle:

Principle #1Segmentation

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

This approach reduces the burden on the photoresist, enabling the formation of fine photomask patterns with high precision and accuracy, overcoming the limitations of conventional photomask blank structures.

Implementation Method 1

the second light-shieldable film comprises a layer primarily composed of a silicon-containing compound that is capable of being etched by fluorine-based dry etching

Methodology Applied

Scientific EffectFluorine-based dry etching:

Implementation Method 2

the first light-shieldable film comprises a layer primarily composed of chromium (Cr) that is not substantially etched by fluorine-based dry etching

Methodology Applied

Scientific EffectChemical resistance to fluorine-based etching:

Data Source

PatentUS7625676B2Photomask blank, photomask and fabrication method thereof

Publication Date: 2009.12.01 SHIN ETSU CHEMICAL CO LTD

AI summary

A light-shieldable film is formed on one principal plane of an optically transparent substrate, and the light-shieldable film has a first light-shieldable film and a second light-shieldable film overlying the first light-shieldable film. The first light-shieldable film is a film that is not substantially etched by fluorine-based (F-based) dry etching and is primarily composed of chromium oxide, chromium nitride, chromium oxynitride or the like. The second light-shieldable film is a film that is primarily composed of a silicon-containing compound that can be etched by F-based dry etching, such as silicon oxide, silicon nitride, silicon oxynitride, silicon/transition-metal oxide, silicon/transition-metal nitride or silicon/transition-metal oxynitride.