Photomask Sub-Resolution Assist Features for Isolated Pattern Process Window

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Solution Overview

Problem

In advanced semiconductor processes, sub-resolution assist features (SRAF) on photomasks often remain on the substrate, affecting the performance of semiconductor devices and reducing the process window in isolated feature regions.

Innovation Solution

A photomask design featuring main patterns with two types of sub-resolution patterns, where the first sub-resolution patterns are perpendicular to the illumination polar axis and the second sub-resolution patterns are parallel, both with a 180-degree phase difference, ensuring they are not imaged onto the photoresist layer, thereby increasing the process window without residue.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If sub-resolution assist features (SRAF) are added to the photomask to increase the process window in isolated regions, then the process window is improved, but the SRAF patterns remain on the substrate and affect device performance

Engineering Contradiction:

Improveprocess windowVSAvoidSRAF residue on substrate

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The sub-resolution assist features are divided into two distinct types: first SRAF patterns extending perpendicular to the illumination polar axis and second SRAF patterns extending parallel to the illumination polar axis. This segmentation allows each type to serve specific functions in enhancing the process window while preventing residue formation on the substrate.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the photomask are assigned different SRAF pattern configurations. The first SRAF patterns are positioned at specific locations relative to isolated features, while the second SRAF patterns are placed in complementary regions. Each pattern type has optimized dimensions and spacing tailored to its local function, enabling selective enhancement without unwanted imaging.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If conventional photomask patterns are used, then the manufacturing process is simple, but the process window in isolated feature regions is reduced

Engineering Contradiction:

Improvephotomask fabrication simplicityVSAvoidprocess window in isolated regions

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The photomask is pre-configured with specifically designed first and second sub-resolution assist feature patterns before the lithography process. These patterns are strategically positioned and dimensioned to proactively enhance the process window for isolated features during exposure, eliminating the need for process adjustments and maintaining manufacturing simplicity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The SRAF patterns are designed with carefully controlled parameters including width, spacing, and phase relationships. The first and second SRAF patterns have specific dimensional parameters that optimize their ability to enhance the process window while remaining below the imaging threshold. Phase differences between the two pattern types are controlled to achieve constructive interference for process window enhancement.

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

This configuration enhances the process window for semiconductor devices by preventing unnecessary imaging of sub-resolution patterns on the substrate, improving the performance and reducing residues in isolated feature regions.

Implementation Method 1

a photomask pattern to the photoresist layer on the wafer

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

a difference between a phase of the first sub-resolution patterns and a phase of the second sub-resolution patterns is 180 degrees

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS20250020993A1Photomask and manufacturing method of semiconductor device

Publication Date: 2025.01.16 POWERCHIP SEMICON MFG CORP

AI summary

A photomask includes a plurality of main patterns, a plurality of first sub-resolution assist feature patterns and a plurality of second sub-resolution assist feature patterns. The first sub-resolution assist feature patterns are located aside the main patterns. The second sub-resolution assist feature patterns are disposed between and connected to adjacent two of the first sub-resolution assist feature patterns.