X-ray Knife Edge Gap Control via Optical Rangefinder Feedback
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Solution Overview
Problem
In X-ray scatterometry, the low angle of incidence results in a large and variable beam footprint, leading to low spatial resolution and accuracy due to limitations in positioning the knife edge close to the sample surface, which cannot be overcome by existing X-ray-based measurement techniques.
Innovation Solution
An optical rangefinder is used to control the size of the gap between the knife edge and the sample surface, allowing precise adjustment and maintenance of the gap size below 1 μm, using a motor driven by control circuitry responsive to optical radiation signals, enhancing the precision of X-ray scatterometry measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the knife edge is positioned very close to the sample surface to reduce beam footprint, then spatial resolution is improved, but the positioning precision and stability are worsened due to mechanical limitations
Solution Approach 1:
The patent replaces the mechanical X-ray-based gap measurement system with an optical measurement system. An optical sensor detects the position of the knife edge relative to the sample surface using optical fields rather than mechanical contact or X-ray measurement, enabling sub-micron positioning precision without mechanical limitations.
Solution Approach 2:
The patent implements a feedback control system where the optical sensor continuously monitors the knife edge position and provides real-time feedback to the positioning system. This closed-loop feedback enables automatic adjustment and stabilization of the knife edge gap at sub-micron precision, overcoming mechanical positioning limitations.
2Area of stationary object
If the knife edge is positioned close to the sample surface, then beam footprint is reduced, but vibrations and fluctuations increase
Solution Approach 1:
The optical sensor and feedback control system continuously monitor and adjust the knife edge position to compensate for vibrations and fluctuations. This active feedback stabilization maintains a stable gap distance even when the knife edge is positioned very close to the sample surface, enabling small beam footprint with high stability.
Solution Approach 2:
Replacing mechanical positioning and measurement systems with optical fields eliminates mechanical play, friction, and contact-induced vibrations. The optical measurement system can detect sub-micron displacements without physical contact, thereby reducing vibration-induced instability.
3Measurement precision
If X-ray-based measurement techniques are used to position the knife edge, then measurement capability is maintained, but positioning precision below 1 μm cannot be achieved
Solution Approach 1:
The patent substitutes X-ray-based measurement with optical measurement for detecting the knife edge position. Optical sensors can resolve sub-micron displacements with higher precision and easier implementation than X-ray interferometry, particularly for the specific task of measuring the air gap between the knife edge and sample surface.
Solution Approach 2:
The patent introduces an optical field as an intermediary measurement medium between the knife edge and the detection system. This optical intermediary enables precise non-contact measurement of sub-micron gaps, avoiding the complexity and limitations of direct X-ray measurement for this specific application.
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 finer spatial resolution and greater precision in X-ray scatterometry measurements by maintaining the gap size with sub-micron resolution, reducing vibrations and fluctuations, and improving the accuracy of scatterometry data.
Implementation Method 1
An optical rangefinder is configured to receive optical radiation reflected from the surface of the sample
Implementation Method 2
A motor is configured to move the knife edge in a direction perpendicular to the surface of the sample
Implementation Method 3
Control circuitry is configured to drive the motor responsively to the signal output by the optical rangefinder
Data Source
AI summary
Apparatus for X-ray scatterometry includes an X-ray source, which directs an X-ray beam to be incident at a grazing angle on an area of a surface of a sample, and an X-ray detector measures X-rays scattered from the area. A knife edge is arranged parallel to the surface of the sample in a location adjacent to the area so as to define a gap between the surface and the knife edge and to block a portion of the X-ray beam that does not pass through the gap. A motor moves the knife edge perpendicular to the surface so as to control a size of the gap. An optical rangefinder receives optical radiation reflected from the surface and outputs a signal indicative of a distance of the knife edge from the surface. Control circuitry drives the motor responsively to the signal in order to regulate the size of the gap.