Low-coherence Fizeau Interferometer with Adjustable Reference Surface
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Solution Overview
Problem
Existing interferometry systems struggle to measure the local variation in strain fields of bowed or curved test elements, such as silicon wafers, due to limitations in resolving interference fringes caused by significant curvature changes.
Innovation Solution
A low-coherence Fizeau interferometer is designed with a test arm and a reference arm that can adjust the power and focus of light to accommodate both flat and curved test elements. This system uses a broad-spectrum low-coherence light source and optical elements that can be adjusted to match the optical path lengths between the test arm and the reference arm, ensuring coherent interference patterns are formed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a flat reference surface is used in a Fizeau interferometer, then the system is simple and easy to operate, but it cannot measure bowed or curved test elements effectively
Solution Approach 1:
The patent applies the dynamics principle by making the reference surface adjustable between flat and curved configurations. The reference surface can be dynamically changed to match the curvature of different test elements (wafer bows), allowing the same interferometer to adapt to various measurement scenarios without requiring multiple fixed reference surfaces. This resolves the contradiction by maintaining operational simplicity while achieving versatility through dynamic adjustment.
2Device complexity
If the interferometer is designed to measure flat substrates, then the optical path is simple, but it cannot resolve interference fringes on bowed or curved surfaces
Solution Approach 1:
The patent applies parameter changes by adjusting the curvature parameter of the reference surface to match the test element being measured. By changing the reference surface from flat to curved with specific radius of curvature values, the system can accommodate different wafer bows and maintain measurable interference fringes. This allows the simple optical path design to achieve precise measurements on curved surfaces by parameter matching rather than requiring complex optical modifications.
3Ease of operation
If optical path lengths between test arm and reference arm are not matched, then the system is easier to operate, but coherent interference patterns cannot be formed
Solution Approach 1:
The patent applies preliminary action by incorporating adjustable optical path length compensation mechanisms that can be pre-configured to match the path lengths between test and reference arms. This preliminary setup ensures that coherent interference patterns can be formed reliably without requiring complex real-time adjustments during operation. The system maintains ease of operation through pre-established path matching while ensuring reliable interference pattern formation.
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 system effectively measures bowed or curved test elements by generating interpretable interference patterns, allowing for the characterization of intra-die strain distribution and improving process yield in semiconductor manufacturing.
Implementation Method 1
a low-coherence light source optically coupled to a first beamsplitter
Implementation Method 2
the first beamsplitter configured to receive light emitted from the low-coherence light source and split the received light into a first portion of light directed to the test arm and a second portion of light directed to the reference arm
Implementation Method 3
a first collimating lens, a flat reference surface, and a test element, the imaging arm optically coupled to the first beamsplitter through a second beam splitter
Implementation Method 4
reflects off a test element. The light that reflects off of the Fizeau surface and the test element then passes through a beamsplitter
Implementation Method 5
The reflection of the first portion of light and the second portion of light interfere forming an interference pattern
Data Source
AI summary
A low-coherence Fizeau interferometer includes a first beamsplitter, a test arm and a reference arm, the first beamsplitter splits light into a first portion of light directed to the test arm and a second portion of light directed to the reference arm, and an imaging arm comprising a first collimating lens, a flat reference surface, and a test element. The test arm focuses the first portion of light at a first focal point, such that a virtual image of the first focal point appears at a focal point of the test element. The reference arm focuses the second portion of light at a second focal point, the first collimating lens collimates the light that then reflects off the flat reference surface. The second beamsplitter directs the first portion of light to reflect off the test element. The reflection of the first and second portion of light form an interference pattern.