Aperture Plate Aberration Detection in Lithographic Scatterometers
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Solution Overview
Problem
Scatterometers, used in lithographic processes for monitoring optical systems, are highly non-linear and require accurate setup of optical components to measure aberrations effectively, but conventional methods like interferometry are time-consuming and difficult to perform during ongoing apparatus use.
Innovation Solution
A method involving an aperture plate with transmissive portions is positioned in the illumination optical system, and the relative positions of bright spots corresponding to these apertures are measured in a conjugate plane in the projection optical system to detect and correct aberrations in the scatterometer's optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometry methods are used to measure aberrations in the scatterometer optical system, then measurement accuracy is improved, but measurement time increases significantly and apparatus downtime increases
Solution Approach 1:
The patent extracts the aberration measurement function from the main scatterometer inspection process by introducing a separate aperture plate with multiple apertures. This allows aberration measurement to be performed independently using a simplified optical path, separating the measurement function from the main inspection function and enabling faster, dedicated aberration characterization without full interferometry setup
Solution Approach 2:
The patent creates a simplified copy of the optical path for aberration measurement purposes. Instead of using the complete complex interferometry setup, a copied and simplified measurement path is established using the aperture plate and detector, which replicates the essential aberration measurement capability with reduced complexity and faster execution time
2Measurement precision
If the scatterometer optical system is frequently calibrated to maintain measurement accuracy, then measurement precision is improved, but device throughput decreases due to calibration downtime
Solution Approach 1:
The patent performs preliminary aberration characterization by measuring aberrations using the aperture plate before actual substrate inspection begins. This preliminary measurement establishes baseline aberration data that can be used to pre-correct or compensate for aberrations during subsequent high-speed substrate inspection, reducing the need for frequent interruptions
Solution Approach 2:
The patent implements periodic aberration measurement at scheduled intervals rather than continuously, using the rapid aperture plate method to characterize aberrations at defined checkpoints. This periodic approach maintains measurement precision while minimizing disruption to substrate throughput, as the fast measurement method requires minimal apparatus downtime
3Measurement precision
If complex interferometry setups are used for aberration measurement, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential aberration measurement capability from the complex interferometry system by using a simplified aperture plate setup. This extraction removes unnecessary complexity while retaining the core function of aberration detection, using only the minimal optical components needed for the specific measurement task
Solution Approach 2:
The patent uses a simple, inexpensive aperture plate with multiple apertures as the measurement tool instead of complex, expensive interferometry equipment. The aperture plate is a simple mechanical component that can be easily manufactured and replaced, providing adequate aberration measurement capability without the complexity and cost of full interferometry systems
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 approach allows for rapid and effective detection of aberrations, enabling periodic calibration and diagnostic monitoring without significant downtime, ensuring accurate measurements and maintaining device throughput.
Implementation Method 1
positioning an aperture plate in a first plane in the illumination optical system... measuring, in a second plane, relative positions of a plurality of bright spots corresponding to the transmissive portions of the aperture plate, the second plane being located in the projection optical system and being conjugate with the first plane
Implementation Method 2
one or more properties of the scattered or reflected beam are measured. By comparing one or more properties of the beam before and after it has been reflected or scattered by the substrate, one or more properties of the substrate may be determined
Implementation Method 3
one or more properties of the scattered or reflected beam are measured. By comparing one or more properties of the beam before and after it has been reflected or scattered by the substrate
Data Source
AI summary
In a scatterometer, an aperture plate comprising an array of transmissive apertures is inserted into a plane in the illumination optical system that is conjugate with the pupil plane of the projection optical system. Aberrations in the optical systems can be measured by measuring the relative positions of bright spots in the pupil plane.