Photomask Assist Feature Layout for Optical Proximity Correction

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Solution Overview

Problem

Sub-wavelength photolithography faces challenges such as image distortion, line-end shortenings, corner rounding, and depth of focus issues due to light scattering and heating problems, particularly in photolithography systems where the dimensions of device structures are shrinking relative to radiation wavelengths.

Innovation Solution

Incorporating assist features, including scattering bars and anti-scattering bars, in non-patterning regions of photo masks to reduce image distortion by blocking or modifying radiation patterns and minimizing heat absorption in lens systems, thereby enhancing image fidelity and resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If photolithography is used with shrinking device dimensions, then device integration density is improved, but image distortion and proximity effects worsen due to light scattering

Engineering Contradiction:

Improvedevice integration densityVSAvoidimage distortion

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

Assist features are introduced as intermediary elements between the main device features and the imaging system. These assist features (scattering bars and anti-scattering bars) mediate the optical interaction by scattering or blocking light to compensate for proximity effects, thereby improving image fidelity without requiring changes to the fundamental photolithography process or the device features themselves

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the optical parameters of the imaging system by introducing features that modify light scattering characteristics. By adjusting the size, position, and material properties of assist features, the optical path and intensity distribution are modified to compensate for distortion caused by sub-wavelength imaging, thereby improving manufacturing precision

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If radiation intensity is increased to improve imaging, then image resolution is improved, but heat absorption and lens heating problems worsen

Engineering Contradiction:

Improveimage resolutionVSAvoidlens heating

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The assist features are strategically placed in specific locations (non-patterning regions) where they can scatter or block radiation locally to improve image resolution in critical areas, while the overall radiation intensity and heat generation across the entire system is managed by limiting the total area of absorbing features

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention converts the harmful effect of light scattering (which causes proximity effects) into a beneficial tool by intentionally introducing assist features that scatter light in controlled ways to compensate for optical distortion, thereby improving image fidelity without requiring excessive radiation intensity that would cause lens heating

Inventive Principle:

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

3Manufacturing precision

If assist features are added to correct optical proximity effects, then manufacturing precision is improved, but photo mask complexity increases

Engineering Contradiction:

Improveoptical proximity correctionVSAvoidphoto mask complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The photo mask is segmented into distinct functional regions: patterning regions containing device features and assist features, and non-patterning regions containing only assist features. This segmentation allows for targeted optical correction in specific areas without unnecessarily complicating the entire mask, as each region can be optimized independently for its specific function

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

The introduction of assist features in non-patterning regions of photo masks effectively reduces image distortion and heat-related issues, improving the resolution and fidelity of photolithography processes, particularly in sub-wavelength applications.

Implementation Method 1

One source of distortion is due to light scattered or otherwise affected by adjacent structures. Distortion in size and shape of the projected image exhibited by this phenomenon is called proximity effect

Methodology Applied

Scientific EffectLight scattering: Scattering

Implementation Method 2

Methodology Applied

Scientific EffectAbsorption of radiation: Absorption (EM radiation)

Implementation Method 3

Methodology Applied

Scientific EffectHeat absorption: Absorption (EM radiation)

Data Source

PatentUS11854808B2Photo mask and lithography method using the same

Publication Date: 2023.12.26 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A photo mask includes a plurality of device features, a first assist feature, and a second assist feature. The device features are in a patterning region of a device region. The first assist feature are in the patterning region and adjacent to the device features. The first assist feature is for correcting an optical proximity effect in a photolithography process. The second assist feature is in a non-patterning region of the device region. The second assist feature is a sub-resolution correction feature, and a first distance between the second assist feature and one of the device features closest to the second assist feature is greater than a second distance between adjacent two of the device features.