Exposure Method Aberration-Weighted Light Source Optimization
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Solution Overview
Problem
Existing exposure methods in semiconductor fabrication face challenges in accurately transferring mask patterns due to residual and fluctuating aberrations in projection optical systems, which affect the edge positions of optical images, and previous techniques fail to account for these aberrations or ensure consistent image performance across different exposure apparatuses.
Innovation Solution
A method that determines a light intensity distribution on the pupil plane of the illumination optical system by generating element light sources and calculating optical images for various aberration states, applying weights to these sources to optimize edge position alignment with target positions, and combining them to form an effective light source for improved image transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional effective light source optimization technique is used, then the margin of exposure and focus position is maximized, but the technique does not account for aberrations in the projection optical system, leading to impractical application
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optical images for multiple aberration states before actual exposure. The system prepares a comprehensive database of predicted optical images corresponding to different aberration conditions, which are then referenced during exposure to determine the effective light source that remains optimal across varying aberration levels.
Solution Approach 2:
The patent employs parameter changes by varying the aberration state parameters in the prediction model to generate multiple optical images under different aberration conditions. By changing the aberration parameters (such as coma, spherical aberration, astigmatism) and recalculating the optical images, the system identifies a light source configuration that maintains performance across the range of expected aberration variations.
2Manufacturing precision
If the projection optical system has residual aberrations, then the aberration correction capability is limited, but the optical image fluctuates synchronously with aberration changes
Solution Approach 1:
The patent implements feedback by using the pre-calculated optical images corresponding to different aberration states as a reference database. During actual exposure, the system references this pre-computed data to determine which effective light source configuration will compensate for the current or expected aberration conditions, thereby stabilizing the optical image despite aberration fluctuations.
Solution Approach 2:
The system performs preliminary calculation of optical images for various aberration states before exposure begins. This advance preparation creates a lookup table of expected optical behaviors under different aberration conditions, enabling rapid selection of the appropriate effective light source without real-time recalibration when aberrations change.
3Reliability
If a light source is optimized for specific aberration response, then the response characteristics to that aberration are minimized, but control of edge positions and guarantee of image performance against unknown aberrations is not ensured
Solution Approach 1:
The patent applies universality by developing an effective light source optimization method that simultaneously addresses multiple aberration types and conditions. The system calculates optical images for various aberration states (coma, spherical aberration, astigmatism, etc.) and determines a light source configuration that performs well across all these conditions, making the solution universally applicable to different aberration scenarios rather than optimized for a single aberration type.
Data Source
AI summary
The present invention provides an exposure method including the steps of generating a plurality of element light sources formed on a pupil plane of an illumination optical system, setting a plurality of aberration states which are expected to exist in a projection optical system, calculating, for each of all combinations of the plurality of aberration states and the plurality of element light sources, an optical image of a pattern of a mask, which is formed in an evaluation area when one aberration state among the plurality of aberration states is produced in the projection optical system, and the pattern of the mask is illuminated with one element light source among the plurality of element light sources, determining, based on the calculated optical images, as a light intensity distribution to be formed on the pupil plane, a light source obtained by combining the plurality of element light sources applied with weights.