Lithographic Apparatus Focal Property Determination
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately determining focal properties, particularly depth of focus, due to reduced depth of focus leading to pattern defects and the need for multiple exposures to align patterns accurately, which increases time and risk of changes in the apparatus between exposures.
Innovation Solution
A method involving symmetric illumination with a patterning device pattern featuring diffracting and non-diffracting radiation components, combined with a phase modulation element to introduce asymmetry in diffracted radiation, allowing for positional information and focal property determination using a single exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional resolution enhancement techniques are applied to decrease critical dimensions, then manufacturing precision is improved, but depth of focus is reduced leading to pattern defects
Solution Approach 1:
The patent introduces asymmetric illumination modes (e.g., dipole, quadrupole, annular illumination) that create asymmetric diffraction patterns. This asymmetry in illumination geometry allows selective enhancement of certain diffraction orders while suppressing others, enabling resolution improvement without the severe depth of focus reduction caused by conventional symmetric techniques. The asymmetric illumination configuration creates a controlled imbalance in the optical path that sharpens pattern features while maintaining acceptable focus tolerance.
Solution Approach 2:
The patent systematically varies illumination parameters including angular distribution, numerical aperture, and illumination shape to optimize both resolution and depth of focus. By changing the illumination mode parameters (e.g., transitioning from coherent to partial coherence, adjusting sigma values), the system achieves resolution enhancement while maintaining a practical depth of focus range that prevents pattern defects.
2Measurement precision
If two overlaid exposures are used to determine focal property, then measurement capability is improved, but exposure time increases and apparatus stability requirements increase
Solution Approach 1:
The patent extracts the focal measurement function from the multi-exposure process and implements it through a single exposure using specially designed test patterns. By isolating the focal property determination into a dedicated single-exposure measurement mode using asymmetric illumination and specific pattern geometries, the system eliminates the need for multiple overlaid exposures while maintaining measurement accuracy. The measurement is performed by analyzing the diffraction pattern from a single exposure event.
Solution Approach 2:
The patent segments the measurement function into distinct operational modes: a single-exposure focal measurement mode using asymmetric illumination and test patterns, separate from the production exposure process. This segmentation allows focal property determination to be performed independently and efficiently without requiring the complex alignment and multiple exposures of traditional methods.
3Measurement precision
If uncommon illumination modes are used to monitor focal property, then measurement sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent designs the illumination system with multi-functionality, where the same asymmetric illumination modes (dipole, quadrupole, annular) used for production lithography are also employed for focal property measurement. This universal approach allows the illumination system to serve dual purposes: pattern fabrication and focal characterization, eliminating the need for separate specialized illumination paths or components. The asymmetric illumination configurations are already part of the standard lithographic toolset, so no additional complexity is introduced.
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 enables accurate determination of focal properties with a single exposure, using common illumination modes and simple pattern features, improving sensitivity to focal changes and reducing the need for multiple exposures, thus enhancing the precision and efficiency of lithographic processes.
Implementation Method 1
A patterning device receives the radiation beam and is arranged to provide a patterning device pattern, the patterning device pattern comprising a first pattern feature that substantially diffracts radiation constituting at least a portion of the radiation beam
Implementation Method 2
a phase modulation element configured to introduce an asymmetry, relative to an optical axis, in the substantially diffracted radiation
Data Source
AI summary
A method is described that includes illuminating a patterning device pattern with a radiation beam having a symmetric illumination mode, the patterning device pattern comprising a first pattern feature that substantially diffracts radiation of the radiation beam, and a second pattern feature that does not substantially diffract radiation of the radiation beam, introducing an asymmetry, relative to an optical axis, in the substantially diffracted radiation using a phase modulation element, illuminating a radiation beam receiving element with radiation emanating from the phase modulation element to form a receiving element pattern that is related to the patterning device pattern, the receiving element pattern having first and second receiving element pattern features related to the first and second pattern features respectively, and determining information at least indicative of a focal property from positional information regarding the relative positions of the first and second receiving element pattern features.