Multi-variable Source Mask Optimization for High NA Lithography

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Solution Overview

Problem

Current lithographic projection systems face challenges in optimizing image quality across different positions of the mask design layout due to through slit pupil variation, which affects imaging precision and consistency, especially in high numerical aperture systems.

Innovation Solution

A multi-variable source mask optimization function is determined using tunable design variables for the illumination source, projection optics, and mask design layout, accounting for imaging variation across multiple positions, and iteratively adjusted until a termination condition related to image quality or pupil shape is satisfied.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If high numerical aperture is used to improve resolution, then imaging precision is improved, but imaging consistency across different positions deteriorates due to through slit pupil variation

Engineering Contradiction:

Improveimaging precisionVSAvoidimaging consistency

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The patent changes the parameters of the illumination source (sigma values, pupil shape, illumination angles) to optimize imaging performance. By adjusting these parameters, the system achieves high numerical aperture for improved resolution while compensating for through slit pupil variation to maintain imaging consistency across different positions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs dynamic optimization by iteratively adjusting design variables and evaluating imaging performance across multiple positions. The system dynamically adapts the illumination and mask parameters to account for position-dependent pupil variations, ensuring consistent imaging quality throughout the field.

Inventive Principle:

Principle #15Dynamics

2Device complexity

If source mask optimization is performed without considering through slit pupil variation, then optimization complexity is reduced, but image quality across multiple positions deteriorates

Engineering Contradiction:

Improveoptimization complexityVSAvoidimage quality

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent segments the optimization process by evaluating imaging performance at multiple discrete positions across the slit (different stripes) and incorporating these position-specific evaluations into the overall optimization function. This segmentation allows the system to account for through slit pupil variation without requiring a completely complex optimization framework.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent creates a universal optimization function that simultaneously considers imaging quality across multiple positions and pupil shape constraints. This multi-functional optimization approach ensures that the derived illumination and mask parameters produce consistent image quality throughout the field while satisfying various performance criteria.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Stability of the object's composition

If iterative adjustment of design variables is performed to optimize image quality, then imaging consistency is improved, but computation time increases

Engineering Contradiction:

Improveimaging consistencyVSAvoidcomputation time

Core Design Contradiction:

Stability of the object's compositionVSLoss of time

Solution Approach 1:

The patent implements feedback by iteratively evaluating the optimization function at multiple positions, comparing the results against target image quality criteria, and adjusting design variables accordingly. This feedback loop continues until convergence is achieved, ensuring imaging consistency while providing a systematic approach to optimization.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary evaluations of imaging performance at multiple positions before finalizing the optimization. By pre-assessing the impact of design variable changes across different positions, the system can make more informed adjustments and potentially reduce the number of iterations required to achieve convergence.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11815808B2Method for high numerical aperture thru-slit source mask optimization

Publication Date: 2023.11.14 ASML NETHERLANDS BV

AI summary

A method for source mask optimization with a lithographic projection apparatus. The method includes determining a multi-variable source mask optimization function using a plurality of tunable design variables for an illumination system of the lithographic projection apparatus, a projection optics of the lithographic projection apparatus to image a mask design layout onto a substrate, and the mask design layout. The multi-variable source mask optimization function may account for imaging variation across different positions in an exposure slit corresponding to different stripes of the mask design layout exposed by a same slit position of the exposure apparatus. The method includes iteratively adjusting the plurality of tunable design variables in the multi-variable source mask optimization function until a termination condition is satisfied.