Phase Grating Asymmetric Contours for Lithography Diffraction
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Solution Overview
Problem
Existing photoelectric position measuring devices face challenges in achieving precise and homogeneous diffraction properties over large surface areas, particularly in lithographic systems where smaller measuring steps and larger wafers require improved measuring path lengths and reduced fluctuation in electrical scanning signals.
Innovation Solution
A phase grating with a periodic array of grating elements featuring an outer contour formed by continuous lines with mutually opposing straight edges and connecting lines forming obtuse angles, which are mirror symmetric and designed to suppress zero-order diffraction by optimizing the surface area ratios and step height, allowing for enhanced diffraction efficiency and homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional grating elements with right-angled contours are used, then manufacturing is simple, but diffraction homogeneity deteriorates over large surface areas
Solution Approach 1:
The patent applies asymmetry by replacing conventional right-angled grating element contours with asymmetric trapezoidal contours featuring obtuse angles. This asymmetric geometry optimizes diffraction properties by reducing zero-order diffraction and enhancing first-order diffraction intensity, achieving homogeneous diffraction across large surface areas while remaining manufacturable through standard photolithography processes.
2Measurement precision
If measuring step size is reduced for higher precision, then measurement resolution improves, but measuring path length decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the obtuse angle parameters of the grating element contours (specifically angles between 90° and 120°) to enhance diffraction efficiency. This allows smaller measuring steps to maintain sufficient first-order diffraction intensity, enabling high measurement precision while preserving adequate measuring path length for lithographic applications.
3Measurement precision
If zero-order diffraction is not suppressed, then manufacturing is easier, but measurement precision deteriorates due to signal fluctuation
Solution Approach 1:
The asymmetric trapezoidal contour with obtuse angles inherently suppresses zero-order diffraction through optimized light distribution. The specific angle geometry (obtuse angles between 90° and 120°) creates destructive interference for the zero-order beam while constructive interference for first-order beams, stabilizing electrical scanning signals without requiring additional suppression mechanisms.
4Measurement precision
If grating element surface area ratio is not optimized, then manufacturing is simpler, but diffraction efficiency decreases
Solution Approach 1:
The patent optimizes the surface area ratio parameter by controlling the obtuse angle geometry of grating elements. The specific angle range (90°-120°) naturally produces optimal surface area distributions that maximize first-order diffraction intensity while remaining compatible with standard semiconductor manufacturing tolerances, eliminating the need for complex multi-parameter optimization.
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 solution enables precise and high-resolution position measurements with reduced zero-order diffraction and increased first-order diffraction intensity, facilitating the use in highly resolving position measuring devices, especially in lithographic systems, by maximizing diffraction efficiency and maintaining homogeneity over large areas.
Implementation Method 1
a first component beam is generated by diffraction at the measuring graduation that is made to interfere with another component beam
Implementation Method 2
The measuring graduation is scanned by a light beam, and the light beam modulated at the measuring graduation as a function of position
Data Source
AI summary
A measuring graduation includes a phase grating for a photoelectric position measuring device for measuring positions in a first direction and in a second direction extending orthogonally to the first direction. The phase grating has a periodic array of grating elements in the first direction and in the second direction. The grating elements each have an outer contour that is formed by a continuous line which includes two mutually opposing first straight edges, two mutually opposing second straight edges extending perpendicularly to the first straight edges, and connecting lines extending between the first straight edges and the second straight edges. The connecting lines form an obtuse angle with the first straight edges and with the second straight edges.