Reflective Relay Optics for Thick-Film Semiconductor Metrology
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Solution Overview
Problem
Existing optical metrology systems struggle to measure critical dimensions and film thicknesses of high aspect ratio semiconductor structures due to low signal-to-noise ratios and limited wavelength penetration, especially in structures with opaque layers, requiring improved methods for high throughput and precision.
Innovation Solution
The use of reflective collection relay optics with demagnification and a collection mask to increase the numerical aperture at the detector, enabling high fringe contrast and sensitivity for thick, multiple layer stacks, while maintaining small collection numerical aperture at the wafer, allowing for measurements with ultraviolet wavelengths down to 140 nanometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical metrology systems are used to measure high aspect ratio structures, then measurement throughput is maintained, but signal-to-noise ratio deteriorates due to limited light penetration into deep structures with opaque layers
Solution Approach 1:
The patent changes the wavelength parameter by introducing vacuum ultraviolet light sources (120-200 nm) that can penetrate opaque layers better than conventional UV or visible light. This parameter change enables light to reach deep structures through opaque material layers, improving signal-to-noise ratio while maintaining measurement capability
Solution Approach 2:
The patent introduces a vacuum environment as an intermediary medium to enable vacuum ultraviolet light transmission. The vacuum ultraviolet light source and detector operate in a vacuum chamber, allowing light to travel through the vacuum to reach deep structures without being absorbed by air molecules, thus improving signal quality
2Measurement precision
If conventional optical systems with large collection numerical aperture are used, then light collection efficiency is improved, but measurement spot size increases and resolution deteriorates
Solution Approach 1:
The patent transitions from conventional refractive optics to reflective relay optics, changing the optical dimension and path. The reflective relay system with demagnification ratio creates a compact measurement spot while maintaining high collection efficiency, resolving the contradiction between spot size and light collection
Solution Approach 2:
The patent uses reflective relay optics to create an optical copy or image of the measurement spot with reduced size. The demagnification ratio < 1 creates a smaller image of the measurement spot at the detector, improving resolution while the reflective path maintains light collection efficiency
3Adaptability or versatility
If conventional refractive collection relay optics are used, then system design is simpler, but wavelength range is limited to 170 nm or higher due to chromatic aberrations
Solution Approach 1:
The patent replaces refractive optical elements with reflective optical elements in the collection relay system. Reflective optics do not suffer from chromatic aberrations, enabling the system to operate across a broader wavelength range including vacuum ultraviolet (120-200 nm) without the wavelength limitations imposed by refractive materials
Solution Approach 2:
The patent changes the optical element material parameter from refractive to reflective surfaces. This parameter change eliminates chromatic aberration limitations and expands the operational wavelength range to include vacuum ultraviolet wavelengths down to 120 nm, improving adaptability across different wavelength regions
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 enhances optical resolution and sensitivity, enabling precise measurement of high aspect ratio structures with reduced measurement spot size and improved signal fidelity, suitable for complex semiconductor devices like NAND and DRAM architectures.
Implementation Method 1
an amount of illumination light is directed from an illumination source to a measurement spot on a surface of the specimen under measurement at one or more angles of incidence
Implementation Method 2
a collection mask, and a dispersive element. The amount of collected light is imaged from the collection mask to the dispersive element through reflective relay optics having a field demagnification greater than one
Implementation Method 3
The amount of collected light is dispersed onto a detector
Data Source
AI summary
Methods and systems for performing spectroscopic ellipsometry measurements of semiconductor structures with reflective collection relay optics having demagnification from the spectrometer slit to the detector are presented herein. The demagnification effectively increases the NA at the detector and reduces the measurement spot size at the wafer imaged onto the detector. In this manner, the demagnification maintains high spectral resolution at the detector, particularly in the ultraviolet wavelength range, e.g., 120-400 nanometers, while maintaining a small collection NA at the wafer, e.g., collection NA less than 0.05. The small collection NA enables high fringe contrast, signal fidelity, and sensitivity, when measuring thick, multiple layer stacks, e.g., 200-300 layers.