Aberration Evaluation for Projection Optical Systems
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Solution Overview
Problem
Conventional methods fail to effectively correct decentering aberrations in projection optical systems when using multi-layer reticles, as they become asymmetrically heated during exposure, leading to difficulties in predicting and correcting asymmetrical aberrations.
Innovation Solution
An evaluation method is introduced that determines whether the illuminated region is symmetrical or asymmetrical, using specific prediction coefficients to evaluate and correct aberrations, incorporating both symmetrical and asymmetrical prediction formulas to account for the asymmetrical heating caused by multi-layer reticles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a multi-layer reticle is used to reduce the number of masks and lower cost, then manufacturing cost is reduced, but the illuminated region becomes asymmetrical causing decentering aberration that cannot be corrected by conventional methods
Solution Approach 1:
The patent applies asymmetry by introducing a decentering amount to the illuminating optical system that matches the asymmetry of the illuminated region. When the illuminated region is asymmetrical, the illuminating optical system is intentionally decentered by a corresponding amount, transforming the asymmetrical heating problem into a correctable symmetrical aberration in the projection optical system.
Solution Approach 2:
The patent changes the parameter of the illuminating optical system's center position (decentering amount) based on the shape of the illuminated region. By dynamically adjusting the decentering amount according to whether the illuminated region is symmetrical or asymmetrical, the system adapts to different reticle configurations and corrects the resulting aberrations.
2Manufacturing precision
If conventional aberration correction methods are used, then symmetrical aberrations can be corrected, but asymmetrical decentering aberrations caused by asymmetrical illumination cannot be evaluated or corrected
Solution Approach 1:
The patent creates a universal aberration evaluation method that handles both symmetrical and asymmetrical cases. The evaluation unit determines the shape of the illuminated region and selects the appropriate prediction formula accordingly, making the system versatile enough to handle different reticle types and illumination configurations.
Solution Approach 2:
The patent performs preliminary determination of the illuminated region's shape before conducting aberration evaluation. By预先 (in advance) identifying whether the region is symmetrical or asymmetrical, the system can select the appropriate prediction formula and decentering amount, enabling accurate correction before exposure begins.
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 accurate evaluation and correction of aberrations, improving the precision and yield of semiconductor devices by accounting for asymmetrical aberrations that were previously difficult to predict and correct.
Implementation Method 1
imaging characteristics change in accordance with a projection optical system absorbing exposure energy
Implementation Method 2
the projection optical system becomes heated asymmetrically in relation to the optical axis, and a decentering aberration occurs
Data Source
AI summary
An evaluation method for evaluating an aberration of a projection optical system in an exposure apparatus is provided. A first prediction coefficient of a first prediction formula for an aberration that is symmetrical with respect to an optical axis of the projection optical system is obtained, and a second prediction coefficient of a second prediction formula for an aberration that is asymmetrical with respect to the optical axis of the projection optical system is obtained. The aberration of the projection optical system is evaluated using the first prediction coefficient in a case where the shape of the illuminated region is determined as symmetrical with respect to the optical axis, and the aberration of the projection optical system is evaluated using the first and the second prediction coefficients in a case where the shape of the illuminated region is asymmetrical with respect to the optical axis.