HHG Source Tunable Spectrum for Metrology Accuracy
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Solution Overview
Problem
Current metrology techniques in lithographic processes face challenges in accurately measuring small product structures due to limitations in wavelength resolution and the size of metrology targets, leading to indirect and potentially inaccurate measurements, especially with the increasing complexity of product structures and layers.
Innovation Solution
A high harmonic generation (HHG) radiation source is configured to control its output emission spectrum by adjusting controllable characteristics of the driving laser pulse, such as bandwidth and central wavelength, to produce discrete harmonic peaks, enhancing spectral resolution and sensitivity for improved measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If visible or near-IR light is used for metrology, then the measurement system can operate with available light sources, but the grating pitch must be much coarser than actual product structures, leading to indirect and potentially inaccurate measurements
Solution Approach 1:
The patent changes the fundamental parameter of light wavelength from visible/near-IR to extreme ultraviolet (EUV) range by using high harmonic generation. This allows the metrology wavelength to match the product structure scale, enabling direct and accurate measurements while maintaining source availability through HHG technology
2Measurement precision
If the wavelength of radiation is decreased to improve measurement performance on smaller structures, then the radiation can resolve smaller structures, but the spectral resolution requirement increases and the system complexity increases
Solution Approach 1:
The patent extracts only the necessary spectral components by selecting specific harmonic orders from the HHG source. This allows using shorter wavelengths for better resolution while maintaining manageable spectral resolution requirements by focusing on discrete harmonic peaks rather than the entire spectrum
Solution Approach 2:
The patent makes the HHG source tunable by adjusting driving laser parameters (pulse duration, intensity, wavelength), allowing dynamic optimization of the emission spectrum to match specific measurement requirements, thereby balancing resolution capability with spectral resolution requirements
3Ease of operation
If metrology targets use features much larger than product structures, then optical metrology techniques can image the targets, but the measurement results are only indirectly related to product structure dimensions and may be inaccurate
Solution Approach 1:
By changing the wavelength parameter to EUV range, the patent enables direct imaging of product structure-sized features without requiring enlarged metrology targets. This eliminates the indirect measurement approach and its associated inaccuracies while maintaining imaging capability
4Measurement precision
If multiple driving laser sources with different central wavelengths are used, then the output emission spectrum can be controlled to produce discrete harmonic peaks, but the device complexity increases
Solution Approach 1:
The patent segments the spectrum into discrete harmonic peaks by using multiple laser sources with different wavelengths, each generating specific harmonic orders. This allows precise control over which spectral components are present, achieving high spectral resolution while managing complexity through structured segmentation
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 more precise measurement of small product structures by optimizing the spectral resolution and sensitivity of the HHG source, enabling accurate overlay and critical dimension measurements even on structures with tight specifications and complex layering.
Implementation Method 1
A HHG source provides illumination radiation for use in a scatterometer. One or more controllable characteristics of a driving laser pulse of the HHG source are configured to control an output emission spectrum of the HHG source.
Data Source
AI summary
Disclosed is a method of performing a measurement in an inspection apparatus, and an associated inspection apparatus and HHG source. The method comprises configuring one or more controllable characteristics of at least one driving laser pulse of a high harmonic generation radiation source to control the output emission spectrum of illumination radiation provided by the high harmonic generation radiation source; and illuminating a target structure with said illuminating radiation. The method may comprise configuring the driving laser pulse so that the output emission spectrum comprises a plurality of discrete harmonic peaks. Alternatively the method may comprise using a plurality of driving laser pulses of different wavelengths such that the output emission spectrum is substantially monochromatic.