EUV Reticle Grating Alignment Detection

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Solution Overview

Problem

The semiconductor industry faces challenges in detecting damages or particles on the burls of an electrostatic chuck in EUV lithography systems, which affect reticle alignment and photoresist layer quality, as existing methods are time-consuming and cannot precisely identify the source of alignment issues.

Innovation Solution

A reticle with a pattern layer featuring plural gratings is used, aligned with the burls, allowing for in-situ detection of burl intactness using optical imaging, reducing the need for development operations and enabling frequent detection during the semiconductor manufacturing process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional detection methods are used to check reticle alignment, then alignment issues can be identified, but the detection process is time-consuming and cannot precisely identify the source of alignment issues

Engineering Contradiction:

Improvealignment issue identification precisionVSAvoiddetection time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The reticle stage is segmented into multiple burls (support structures), and each burl is individually monitored through corresponding gratings. This segmentation allows precise identification of which specific burl causes alignment issues, rather than detecting only general misalignment. The patent divides the detection problem into discrete locations that can be independently analyzed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces conventional mechanical alignment detection methods with an optical detection system. Light beams are directed through the reticle and detected by sensors to create images of the gratings, enabling non-contact, high-precision measurement of burl positions and integrity without mechanical interference or time-consuming procedures.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If frequent detection of burl integrity is performed, then the quality of patterned photoresist layer can be improved, but existing detection methods require development operations that are time-consuming

Engineering Contradiction:

Improvephotoresist layer qualityVSAvoiddetection and development time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary detection of burl integrity using optical imaging before the actual lithography process. By detecting potential alignment issues and burl damages in advance, the system can prevent defects in the photoresist layer without requiring time-consuming development operations after each exposure cycle.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The reticle itself serves as the detection medium through its integrated grating structures. The gratings are built into the reticle design, allowing the reticle to provide its own alignment and integrity information when illuminated, eliminating the need for separate detection equipment or development processes.

Inventive Principle:

Principle #25Self-service

3Loss of information

If conventional reticle alignment checking is performed ex-situ, then alignment residues can be measured, but the method cannot precisely point out which part of the lithography apparatus causes poor alignment

Engineering Contradiction:

Improvealignment issue location informationVSAvoidalignment source identification precision

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system provides immediate feedback about burl integrity and alignment status through optical imaging and sensor detection. The detected image information is processed to identify specific burls with alignment issues, providing actionable feedback that pinpoints the exact location and cause of problems without ambiguous results.

Inventive Principle:

Principle #23Feedback

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 method allows for precise, time-efficient detection of burl integrity, improving the quality of the patterned photoresist layer by identifying and addressing alignment issues directly within the lithography apparatus.

Implementation Method 1

a reticle of an extreme ultraviolet (EUV) lithography system is usually applied to form desired pattern onto a photoresist layer

Methodology Applied

Scientific EffectLight reflection: Reflection

Implementation Method 2

directs a light beam of the light source toward a transmission image sensor (TIS), so as to form an aerial image of the pattern layer

Methodology Applied

Scientific EffectOptical imaging: Lens

Data Source

PatentUS11221562B2Reticle and method of detecting intactness of reticle stage using the same

Publication Date: 2022.01.11 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

In some embodiments, a reticle structure is provided. The reticle structure includes a reticle stage and a reticle mounted on the reticle stage. The reticle stage includes plural first burls and plural second burls, in which the second burls are disposed on a center of the reticle stage and the first burls disposed on an edge of the reticle stage such that the first burls surround the second burls. The reticle includes a base material and a pattern layer overlying the base material. The base material is secured on the first and second burls of the reticle stage. The pattern layer includes plural first gratings, and each of the first burls is vertically aligned with one of the first gratings.