Diffractive Structure Axial Focus Distance Measurement
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Solution Overview
Problem
Existing methods for measuring the distance between two parallel planes, particularly in a mask positioner, lack precision and require contact, which can be damaging and inaccurate.
Innovation Solution
A method utilizing a diffractive structure with a special amplitude and/or phase structure illuminated by collimated light to generate an axial focus that is tilted, allowing for non-contact measurement by determining the distance from the position of the axial focus's impact point, using equations based on angular relationships and optionally with a scale for precise determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact-based measurement methods are used to determine distance between planes, then measurement can be performed, but measurement precision is insufficient and damage risk increases
Solution Approach 1:
The patent replaces mechanical contact-based measurement methods with an optical measurement system. A diffractive structure is illuminated with collimated light to generate an axial focus that extends to the measurement plane, allowing non-contact distance determination through optical means. This substitution eliminates mechanical contact, preventing damage to measured surfaces while achieving high precision through the controlled optical focus.
2Measurement precision
If conventional optical methods are used for distance measurement, then non-contact measurement is achieved, but measurement precision is insufficient
Solution Approach 1:
The patent achieves high precision by carefully controlling and optimizing specific parameters of the diffractive structure, including the groove depth, groove spacing, and tilt angle α. By adjusting these parameters, the axial focus can be precisely positioned and its extent controlled to match the measurement distance, enabling accurate non-contact measurement without requiring complex additional optical components.
Solution Approach 2:
The patent introduces a tilted axial focus that extends in both axial and lateral dimensions. The focus is inclined at an angle α relative to the optical axis, creating a spatial configuration where the focus extends from the reference plane to the measurement plane. This dimensional approach allows distance determination through lateral displacement measurement at the impact point, simplifying the overall measurement system.
3Measurement precision
If a tilted axial focus is generated using a diffractive structure, then non-contact high-precision measurement is enabled, but the diffractive structure design becomes more complex
Solution Approach 1:
The diffractive structure is designed with discrete grooves or ridges that can be fabricated using standard microlithography and etching techniques. The structure consists of periodic elements with specific depths and spacing, which can be manufactured by dividing the complex optical function into simple, repeatable geometric features. This segmentation approach makes the diffractive structure compatible with conventional semiconductor manufacturing processes.
Solution Approach 2:
The diffractive structure serves multiple functions simultaneously: it diffracts incident collimated light to generate the tilted axial focus, the tilt angle α is determined by the groove geometry, and the focus extent is controlled by the groove depth. This multi-functionality is achieved within a single manufactured component, eliminating the need for separate optical elements and simplifying the overall device fabrication.
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 high-precision non-contact measurement of the distance between planes, reducing the risk of damage and improving accuracy through the use of inclined axial foci and quantized phase functions, suitable for applications like photolithography.
Implementation Method 1
at least one axial focus is generated by illuminating a diffractive structure arranged in the reference plane
Implementation Method 2
the axial focus is reflected back to the reference plane at the measurement plane
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A method for measuring a distance (d) between a reference plane (1) and a measurement plane (3) parallel to the reference plane (1) is specified, in which at least one axial focus (5) which is inclined at an angle α in relation to an axis perpendicular to the reference plane (1) and the measurement plane (3) is generated by illuminating a diffractive structure (2) arranged in the reference plane (1). The distance (d) is established from the position of an impact point of the at least one axial focus (5) in the measurement plane (3) or from the position of an impact point in the reference plane (1) of the axial focus (5) reflected on the measurement plane (3). Furthermore, a device, which is suitable for the method, for measuring a distance (d) between a reference plane (1) and a measurement plane (3) parallel to the reference plane (1) is specified.