Edge Registration for Interferometry Metrology
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Solution Overview
Problem
Conventional methods for precision edge registration of optical surfaces in metrology lack repeatability and accuracy, especially for reflective components, leading to accumulated errors in high-performance electronics fabrication due to non-uniform thickness and clamping issues.
Innovation Solution
A metrology apparatus using collimated light, imaging lenses, spatial filtering, and a sensor array to achieve precise edge registration through bright field and dark field imaging, enabling accurate detection of component edges and flatness characterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used for surface flatness characterization, then the measurement process is simple, but measurement precision and accuracy are insufficient for high-performance electronics fabrication
Solution Approach 1:
The apparatus segments the measurement function into multiple specialized components: an illumination system for light delivery, imaging lenses for focal plane control, a spatial filtering element for signal purification, and a sensor array for data capture. Each component performs a specific function that collectively achieves high measurement precision without requiring the entire system to be overly complex.
Solution Approach 2:
The spatial filtering element acts as an intermediary between the imaging lenses and sensor array, selectively transmitting or blocking light based on spatial frequency. This intermediary component enables precise edge detection by filtering out unwanted spatial frequencies while preserving the signal needed for accurate surface flatness characterization.
2Manufacturing precision
If fiducial or alignment marks are used for registration, then alignment can be achieved on one side, but they cannot be used on both sides and require later stages in mask patterning
Solution Approach 1:
The apparatus enables the optical component to register itself through its own physical features (edges and surfaces) without requiring external fiducial marks. The edge detection capability allows the component to provide its own registration reference, making the method applicable at any stage of mask patterning and on both sides of the component.
Solution Approach 2:
The system utilizes optical contrast changes (analogous to color changes) by detecting variations in light reflection and interference patterns at edges. This allows the apparatus to identify and register component edges based on their optical properties rather than requiring physical marks, providing versatility across different mask stages and surfaces.
3Measurement precision
If the component is re-positioned for multiple measurements to compensate for weight and clamping errors, then measurement accuracy can be improved, but the time required for measurement increases
Solution Approach 1:
The apparatus performs preliminary edge detection and registration before the full flatness measurement process. By establishing accurate edge registration in advance, the system eliminates the need for multiple re-positioning operations, as the component can be measured accurately in a single positioned state. This preliminary registration action reduces the total measurement cycle time while maintaining precision.
4Reliability
If electrostatic clamping is used to hold the component, then the component can be secured, but thickness variations are transferred between surfaces compounding measurement error
Solution Approach 1:
The apparatus replaces mechanical contact-based positioning with optical field-based measurement. By using non-contact optical methods to detect edge positions and surface flatness, the system avoids the mechanical coupling that transfers thickness variations. The electrostatic clamping remains for securing the component, but the measurement process itself does not rely on mechanical contact that would propagate thickness errors.
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
The apparatus provides sub-pixel accuracy in edge registration and surface flatness characterization, reducing measurement errors and improving the precision of optical component positioning, thus enhancing the accuracy of metrology processes.
Implementation Method 1
an illumination source that directs collimated light to a reference surface and to an optical component having a test surface
Implementation Method 2
a first imaging lens that defines a Fourier transform plane for light reflected from the reference surface and the test surface
Implementation Method 3
a spatial filtering element that is actuable to a blocking position that blocks specular light at the transform plane
Implementation Method 4
a second imaging lens that forms, at an image plane, an image of the test surface
Implementation Method 5
a sensor array disposed to generate image data from received light at the image plane
Implementation Method 6
metrology methods have been developed to characterize features such as surface flatness using interferometry
Data Source
AI summary
A metrology apparatus has an illumination source that directs collimated light to a reference surface and to an optical component having a test surface that is in parallel with the reference surface. A first imaging lens defines a Fourier transform plane for light reflected from the reference surface and the test surface. A spatial filtering element is actuable to a blocking position that blocks specular light at the transform plane. A second imaging lens forms, at an image plane, an image of the test surface. A sensor array generates image data from received light at the image plane.