Off-Axis Illumination Profile for Reduced-Pitch Mark Position Measurement

Solution Overview

Problem

Current lithographic apparatuses face challenges in accurately measuring the positions of marks on substrates with reduced pitch grating lines, which is essential for precise overlay control as feature sizes decrease, while maintaining compatibility with existing mark types and infrastructure without compromising throughput.

Innovation Solution

A position measurement method and apparatus using off-axis illumination with a self-referencing interferometer, where radiation from source regions confined to the peripheral portion of the objective lens's pupil is used to form a spot on the mark, allowing for accurate detection of position variations and calculation of mark positions, compatible with both reduced and conventional pitch marks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the pitch of grating lines in alignment marks is reduced to improve measurement precision for smaller features, then measurement precision improves, but device complexity and infrastructure requirements increase

Engineering Contradiction:

Improveposition measurement precisionVSAvoidsensor and infrastructure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The alignment sensor is designed to measure both reduced-pitch marks and conventional-pitch marks using the same optical system and detector. By configuring the illumination to use peripheral pupil regions, the sensor achieves diffraction patterns suitable for reduced-pitch marks while maintaining compatibility with existing conventional marks, eliminating the need for separate measurement systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The illumination configuration is changed to use source regions confined to the peripheral portion of the pupil, specifically at least two diametrically opposed off-axis source regions. This parameter change in the illumination geometry enables the system to achieve the necessary diffraction patterns for reduced-pitch marks without requiring a complete redesign of the measurement apparatus.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a new sensor design is implemented to measure reduced pitch marks, then measurement precision improves, but ease of operation and compatibility with existing marks deteriorate

Engineering Contradiction:

Improveposition measurement precisionVSAvoidcompatibility with existing mark types

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The alignment sensor is designed to measure both reduced-pitch marks and conventional-pitch marks using the same optical system and detector. By configuring the illumination to use peripheral pupil regions, the sensor achieves diffraction patterns suitable for reduced-pitch marks while maintaining compatibility with existing conventional marks, eliminating the need for separate measurement systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of operation

If conventional illumination methods are used, then ease of operation is maintained, but measurement precision for reduced pitch marks deteriorates

Engineering Contradiction:

Improveoperational simplicityVSAvoidposition measurement precision

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The illumination configuration is changed to use source regions confined to the peripheral portion of the pupil, specifically at least two diametrically opposed off-axis source regions. This parameter change in the illumination geometry enables the system to achieve the necessary diffraction patterns for reduced-pitch marks without requiring a complete redesign of the measurement apparatus.

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

Enables accurate position measurement of marks with a wide range of pitches from 1 μm to 20 μm without altering existing detector designs, improving measurement precision and compatibility with various mark types while maintaining throughput.

Implementation Method 1

receiving radiation diffracted by the mark via the same objective lens

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

processing the diffracted radiation in a self-referencing interferometer

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS9970747B2Position measurement with illumination profile having two diametrically opposed off-axis radiation

Publication Date: 2018.05.15 ASML NETHERLANDS BV

AI summary

An apparatus (AS) measures positions of marks (202) on a lithographic substrate (W). An illumination arrangement (940, 962, 964) provides off-axis radiation from at least first and second regions. The first and second source regions are diametrically opposite one another with respect to an optical axis (O) and are limited in angular extent. The regions may be small spots selected according to a direction of periodicity of a mark being measured, or larger segments. Radiation at a selected pair of source regions can be generated by supplying radiation at a single source feed position to a self-referencing interferometer. A modified half wave plate is positioned downstream of the interferometer, which can be used in the position measuring apparatus. The modified half wave plate has its fast axis in one part arranged at 45° to the fast axis in another part diametrically opposite.