Acidic Immersion Fluid for Lithography Resolution

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Solution Overview

Problem

Conventional photolithographic systems face limitations in resolution enhancement due to physical and technical constraints, particularly with the numerical aperture (NA), and immersion lithography requires a high-index fluid that must be chemically compatible and control pH to prevent contamination of photoresists and dissolution of optical lens materials.

Innovation Solution

An immersion fluid with a pH less than 7 is used in immersion lithographic systems to reduce hydroxyl ion concentration and prevent lens material dissolution, ensuring chemical compatibility and improved resolution by maintaining the integrity of photo-generated catalysts and optical components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If water is used as immersion fluid to increase numerical aperture, then resolution is improved, but photoresist is contaminated by hydroxyl ions and lens material dissolves

Engineering Contradiction:

ImproveresolutionVSAvoidphotoresist contamination and lens material dissolution

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the chemical parameters of the immersion fluid by controlling the pH to be less than 7 (acidic condition), which fundamentally alters the chemical interactions between the fluid and the photoresist/lens materials, preventing hydroxyl ion contamination and lens dissolution while maintaining the high index of refraction needed for improved resolution

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful effect of water (which causes contamination and dissolution) into a beneficial acidic environment by controlling pH, where the acidity actually protects the photoresist from base contamination and prevents lens material dissolution, while still allowing the high index of refraction to improve resolution

Inventive Principle:

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

2Manufacturing precision

If high-index fluid is used to increase numerical aperture, then resolution is improved, but chemical compatibility with photoresist and optical elements becomes difficult to achieve

Engineering Contradiction:

ImproveresolutionVSAvoidchemical compatibility

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the chemical parameters by specifying pH < 7, which fundamentally alters the chemical compatibility profile of the high-index fluid, allowing it to be chemically compatible with both photoresist and optical elements while maintaining the high index of refraction needed for improved resolution

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 use of an immersion fluid with a pH less than 7 enhances the resolution of photolithographic systems by suppressing acid catalyst depletion and reducing lens material dissolution, resulting in better resist profiles and maintaining equipment functionality.

Implementation Method 1

an immersion fluid with a pH less than 7 contacts at least a portion of the optical surface

Methodology Applied

Scientific EffectpH control:

Implementation Method 2

Photoresists, particularly chemically amplified photoresists, may be contaminated by hydroxyl ions (OH−) present in the immersion fluid or water

Methodology Applied

Scientific EffectHydroxyl ion suppression:

Implementation Method 3

the numerical aperture NA is given by the NA=n sin θ... a substrate to be patterned is immersed in a high-index fluid or an immersion medium, such that the space between the final optical element or lens and the substrate is filled with a high-index fluid (n>1)

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS7700267B2Immersion fluid for immersion lithography, and method of performing immersion lithography

Publication Date: 2010.04.20 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An immersion lithographic system 10 comprises an optical surface 51, an immersion fluid 60 with a pH less than 7 contacting at least a portion of the optical surface, and a semiconductor structure 80 having a topmost photoresist layer 70 wherein a portion of the photoresist is in contact with the immersion fluid. Further, a method for illuminating a semiconductor structure 80 having a topmost photoresist layer 70 comprising the steps of: introducing an immersion fluid 60 into a space between an optical surface 51 and the photoresist layer wherein the immersion fluid has a pH of less than 7, and directing light preferably with a wavelength of less than 450 nm through the immersion fluid and onto the photoresist.