Ellipsometer Scheimpflug Aperture for Circular Spot Imaging
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Solution Overview
Problem
Existing systems for reflectometers, ellipsometers, and polarimeters fail to achieve focused imaging over a large area when electromagnetic radiation is incident at an oblique angle, particularly in maintaining a circular spot shape on the sample surface.
Innovation Solution
The system meets the Scheimpflug condition by orienting the aperture, focusing means, and sample stage such that the projected planes of these components intersect, with the aperture rotated to ensure a beam incidence angle that maintains a unity aspect ratio spot on the sample, using the equation Tan(α)=(X−f)/f Tan(β), and applying this condition on both the incident and reflection sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If electromagnetic radiation is directed to a sample at an oblique angle of incidence with a circular beam at the source, then the beam covers a large area on the sample, but the spot appears as an ellipse and cannot be in focus over the entire area
Solution Approach 1:
The aperture is intentionally given an elliptical shape (asymmetric geometry) to compensate for the oblique angle of incidence. When the beam passes through this elliptical aperture at the calculated oblique angle, the ellipse is transformed into a circle on the sample surface, allowing the entire spot area to be in focus.
Solution Approach 2:
The invention introduces the aperture plane as an additional dimensional element between the circular beam source and the sample surface. By orienting this intermediate plane at a specific angle relative to the beam direction, the system transforms the beam cross-section shape from circular to elliptical to circular again on the sample, achieving focus across the entire area.
2Shape
If an elliptically shaped aperture is used to preshape the beam, then a circular spot can be achieved on the sample, but the system complexity increases
Solution Approach 1:
Instead of using complex mechanical adjustments or multiple optical elements, the invention achieves the desired circular spot shape by simply changing the geometric parameters of a single aperture element - specifically, using an ellipse with a defined aspect ratio and orientation angle. This parameter-based solution is mathematically determined and easily implemented.
3Shape
If the aperture is rotated to appear as an ellipse to the beam, then the spot shape on the sample can be controlled, but the alignment precision required increases
Solution Approach 1:
The aperture orientation angle is pre-calculated based on the desired spot aspect ratio and beam incidence angle using the provided mathematical relationships. This preliminary determination of the optimal angle eliminates the need for complex real-time adjustments or high-precision alignment mechanisms during operation.
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 configuration ensures that the electromagnetic radiation spot is in focus over a substantial area on both the sample and detector, achieving a circular spot with every point in focus, enhancing imaging quality and precision.
Implementation Method 1
a focusing means; and said beam passes through said focusing means and impinges upon a sample
Implementation Method 2
the aperture is rotated such that the beam locus is oriented at an angle (α) with respect to a perpendicular to said plane of the aperture
Data Source
AI summary
A reflectometer, ellipsometer, polarimeter or the like system with aperture, focusing means, sample and optionally detector planes oriented so that the Scheimpflug condition is substantially met on incident and/or, optionally, reflection sides of a sample. In addition beneficial aperture hole aspect ratio and aperture plane orientation is described.