Lensless EUV Inspection for 3D Structure Depth Retrieval
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Solution Overview
Problem
Current inspection methods in lithographic processes are inadequate for measuring three-dimensional properties of product structures, particularly at deep ultraviolet or extreme ultraviolet wavelengths, as they fail to provide accurate depth information and are limited by the need for imaging optics, which are challenging for shorter wavelengths.
Innovation Solution
The implementation of optical coherence tomography (OCT) using a numerical phase retrieval algorithm for lensless imaging, allowing the capture and reconstruction of three-dimensional product structures from the amplitude and phase of reflected frequency spectra, enabling depth information retrieval without traditional interferometric detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical metrology techniques are used, then measurement speed is high, but depth information and three-dimensional properties cannot be obtained
Solution Approach 1:
The patent extracts the imaging function from the detection system by removing traditional imaging optics. Instead of using lenses and mirrors to form images, the system captures diffraction patterns directly and reconstructs three-dimensional information computationally through numerical phase retrieval algorithms, thereby eliminating the need for complex imaging optics while still obtaining depth information
Solution Approach 2:
The patent replaces the mechanical/optical imaging system with a computational imaging approach. The physical imaging process is substituted by numerical algorithms that reconstruct three-dimensional structures from diffraction patterns, transforming a hardware-based solution into a software-based solution that achieves the same measurement goal
2Measurement precision
If scanning electron microscopy is used to resolve small features, then measurement precision is high, but productivity is low due to time consumption
Solution Approach 1:
The patent employs periodic scanning of the radiation beam across the substrate surface, systematically measuring diffraction patterns at multiple positions. This periodic measurement approach enables comprehensive three-dimensional characterization of multiple product structures in a systematic manner, achieving both high resolution and improved throughput compared to point-by-point SEM imaging
Solution Approach 2:
The patent changes the wavelength parameter of the radiation to deep ultraviolet or extreme ultraviolet ranges, which provides sufficient resolution for modern product structures while enabling faster optical-based measurement speeds compared to electron microscopy. This parameter change allows the system to achieve SEM-level resolution with optical-speed measurement
3Measurement precision
If dedicated metrology targets are used, then measurement of specific properties is accurate, but adaptability to measure real product structures is limited
Solution Approach 1:
The patent creates a universal measurement system that can measure both dedicated metrology targets and real product structures using the same methodology. The lensless diffraction-based approach with numerical phase retrieval works for any periodic or aperiodic structure, making the system adaptable to various measurement needs without requiring different measurement techniques for different target types
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 enables accurate three-dimensional imaging and measurement of product structures at EUV wavelengths, overcoming the limitations of existing methods by providing depth information and avoiding the need for imaging optics, thus improving the precision of lithographic process control.
Implementation Method 1
capturing a plurality of diffraction patterns formed by said radiation after scattering by the three-dimensional product structure
Implementation Method 2
The implementation of optical coherence tomography (OCT) using a numerical phase retrieval algorithm for lensless imaging, allowing the capture and reconstruction of three-dimensional product structures from the amplitude and phase of reflected frequency spectra
Data Source
AI summary
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithographic apparatus has an inspection apparatus with an EUV radiation source. The radiation source emits a radiation beam that includes coherent radiation of a specific wavelength. The beam propagates to illumination optical system, which focuses the radiation beam into a focused beam of illuminating radiation. The illumination optical system illuminates a three-dimensional product structure on the substrate, which scatters the illuminating radiation. On the surface of a detector, the radiation scattered by the product structure forms a diffraction pattern that is used to reconstruct data describing the three-dimensional product structure.