X-ray reflectometry apparatus for 3D nanostructure measurement
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Solution Overview
Problem
Conventional X-ray reflectometry methods face challenges in accurately measuring three-dimensional nanostructures on flat substrates due to issues with lateral coherence length and off-specular scattering, which complicates the analysis of complex 3D structures.
Innovation Solution
An X-ray reflectometry apparatus and method utilizing a 2D detector to collect specularly and off-specularly reflected X-rays, with a fan-shaped X-ray beam focused onto the sample at adjustable incident angles, allowing for the removal of off-specular contributions and integration of specular reflection intensity to obtain structure information, combined with single transmission small-angle X-ray scattering data for lateral length scale input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional X-ray reflectometry uses a large slit width to increase signal intensity, then the measurement sensitivity improves, but off-specular scattering intensity spills over into the measured specular reflectivity, causing measurement errors
Solution Approach 1:
The patent segments the detection process by using a 2D detector to separate specular and off-specular scattering signals spatially. The detector records intensity at different azimuthal angles, allowing the specular component (at zero azimuthal angle) to be isolated from off-specular contributions (at non-zero azimuthal angles), thereby eliminating the harmful spill-over effect while maintaining high signal intensity.
2Device complexity
If conventional methods use fixed incident angles to simplify measurement, then the device complexity is reduced, but the ability to analyze complex 3D nanostructure morphology is limited
Solution Approach 1:
The patent implements dynamic measurement capability by enabling continuous variation of the incident angle θ and azimuthal angle φ. The apparatus can scan through different angular configurations to collect reflectivity data from multiple directions, allowing reconstruction of complex 3D nanostructure morphology. This dynamic angular control provides versatility for analyzing various 3D structures while maintaining a relatively simple optical path configuration.
3Measurement precision
If conventional XRR uses coherent X-ray beams to achieve high resolution, then the lateral coherence length is sufficient for line gratings, but it becomes inadequate for 3D nanostructures without preferred orientation
Solution Approach 1:
The patent transitions from relying solely on lateral coherence (x-y plane) to utilizing angular coherence in three dimensions. By measuring reflectivity as a function of both incident angle θ and azimuthal angle φ, the method effectively uses the angular dimension to compensate for limited lateral coherence length. This allows 3D nanostructures without preferred orientation to be characterized, as the angular scanning captures structural information from all lateral directions.
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
Enables precise measurement of critical dimensions and material composition of 3D nanostructures with high resolution (less than 0.1 nm) by analyzing electron density along the z-direction and integrating incident X-ray intensity at different azimuthal angles, effectively mitigating the limitations of conventional methods.
Implementation Method 1
X-ray reflectometry apparatus for measuring three dimensional nanostructures on a flat substrate includes an X-ray source for emitting an X-ray with a wavelength larger than 0.154 nanometers (nm), and an X-ray reflector for point focusing a fan-shape X-ray onto a surface of a sample
Implementation Method 2
The incident slit is between the X-ray reflector and the sample, the width of the incident slit is greater than its opening by a factor 10 or above, and the width of the incident slit is aligned perpendicular to the reflection plane of the X-ray. The opening angle of the incident X-ray is controlled via the incident slit opening, and the divergence angle of the fan-shape incident X-ray is controlled via the width of the incident slit
Implementation Method 3
The X-ray detector has a fine pixel resolution for collecting the X-ray reflected by the surface of the sample, wherein at each azimuthal position of the reflected X-ray collected on the X-ray detector, the off-specular contribution is determined and removed from the reflected X-ray intensity
Data Source
AI summary
This disclosure relates to an apparatus and methods for applying X-ray reflectometry (XRR) in characterizing three dimensional nanostructures supported on a flat substrate with a miniscule sampling area and a thickness in nanometers. In particular, this disclosure is targeted for addressing the difficulties encountered when XRR is applied to samples with intricate nanostructures along all three directions, e.g. arrays of nanostructured poles or shafts. Convergent X-ray with long wavelength, greater than that from a copper anode of 0.154 nm and less than twice of the characteristic dimensions along the film thickness direction, is preferably used with appropriate collimations on both incident and detection arms to enable the XRR for measurements of samples with limited sample area and scattering volumes.