Interferometric Surface Profile Correction for Multi-Material Objects
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Solution Overview
Problem
Optical profilometry struggles to accurately measure the profile of surfaces with structures made of different materials due to phase shifts in reflection, leading to erroneous height measurements, and existing correction methods require a priori knowledge and are cumbersome.
Innovation Solution
A method that determines a correction function using interferometric measurements from a metallized and a non-metallized reference surface, applied to the surface of interest to correct for phase shifts, allowing for accurate relative height measurement without prior knowledge of material nature or geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric measurements are used to measure surface profile, then measurement capability is provided, but measurement precision deteriorates when different materials are present due to phase shifts
Solution Approach 1:
The patent introduces an intermediary correction function that mediates between the interferometric measurement signal and the true surface profile. This correction function, derived from reference measurements on metallized and non-metallized surfaces, acts as a translator that converts material-dependent phase shifts into material-independent height corrections, enabling accurate measurement across different materials without requiring prior knowledge of material properties
Solution Approach 2:
The patent changes the measurement parameter by introducing a correction function that transforms the raw interferometric phase data into corrected height values. By applying this correction function derived from reference surfaces, the measurement system adapts to different material properties dynamically, converting the harmful phase shift parameter into useful correction information that improves measurement accuracy across diverse materials
2Measurement precision
If theoretical reflection phase models are used to correct measurements, then correction capability is provided, but device complexity and operational difficulty increase
Solution Approach 1:
The patent creates simplified copies of the measurement process using reference surfaces that are metallized and non-metallized versions of the same surface. By copying the measurement procedure on these reference surfaces and deriving a correction function from the difference, the system avoids the need for complex theoretical models while still achieving accurate correction. This empirical copying approach replaces complicated a priori knowledge requirements with simple reference measurements
Solution Approach 2:
The measurement system performs self-correction by using its own measurements on reference surfaces to generate the correction function. The system serves itself by automatically deriving the correction needed from the reference measurements, eliminating the need for external theoretical models or manual intervention. This self-service mechanism simplifies the correction process while maintaining high accuracy
3Measurement precision
If multiple reference objects are metallized for correction, then correction accuracy is improved, but material loss increases
Solution Approach 1:
The patent merges the correction function derivation process into a single reference object by measuring both the metallized and non-metallized surfaces of the same object. This consolidation approach allows the correction function to be derived from one reference object rather than requiring multiple separate reference objects, thereby reducing material consumption while maintaining correction accuracy. The merged measurement approach on a single object provides sufficient information for accurate correction
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 accurate measurement of relative heights on surfaces with multiple materials by correcting for phase shifts, improving measurement precision and reducing the need for costly modifications or a priori information, while minimizing the number of metallized reference objects used.
Implementation Method 1
measurement, then the study, of an interferometric signal obtained between a reference optical radiation and an optical inspection radiation from the same source, sent respectively towards a reference surface and towards the inspected surface, and reflected by said surfaces
Implementation Method 2
the wave reflected on the surface of the object undergoes a phase shift which depends on the physical characteristics of the materials, such as their complex indices of refraction
Data Source
Figure 1
Figure 2~3b
Figure 4a
AI summary
The present invention relates to a method (100) for measuring the profile of a surface (400) of an object (300) to be measured, particularly comprising zones made of at least two different materials, the object (300) to be measured being part of a plurality of substantially identical objects, the plurality of objects further comprising at least one reference object (304, 306) which has at least one reference surface, the method (100) comprising the steps of: - establishing (102) a correction function, on the basis of a first profile signal of a first reference surface and a second profile signal of a second reference surface, the second reference surface being metal-coated; - acquiring (110) a profile signal of the surface of the object to be measured; and - applying (116) the correction function to the profile signal of the surface (400) of the object (300) to be measured in order to obtain a corrected profile signal; the profile signals being obtained from interferometric measurements (104, 112). The invention also relates to a device for measuring the profile of a surface of an object using such a method.