Three-DOF Heterodyne Grating Interferometer for Lithography Stages
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Solution Overview
Problem
Current dual-frequency laser interferometer systems used in ultra-precision workpiece stages face challenges such as environmental sensitivity, complexity, high cost, and limited accuracy in measuring dynamic characteristics, making them unsuitable for high-precision and high-speed applications in semiconductor manufacturing.
Innovation Solution
A three-DOF heterodyne grating interferometer system utilizing a dual-frequency laser, a grating interferometer with a polarizing beam splitter, and two-dimensional reflection gratings, along with an electronic signal processing component, to achieve simultaneous measurements of three-linear displacements with subnanometer accuracy and a simple structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dual-frequency laser interferometer measurement system is used to measure multi-DOF displacements of the ultra-precision workpiece stage, then measurement capability for high-speed, high acceleration, large stroke, ultra-precision, and multi-DOF movements is achieved, but environmental sensitivity increases, measurement speed improvement becomes difficult, space occupation increases, cost increases, and dynamic characteristics measurement capability deteriorates
Solution Approach 1:
The patent changes the measurement wavelength parameter by using green light (532nm) instead of traditional infrared light, which reduces environmental sensitivity while maintaining measurement precision. This parameter change allows the system to achieve sub-nanometer accuracy while being less susceptible to environmental disturbances.
Solution Approach 2:
The patent replaces the traditional mechanical dual-frequency laser interferometer system with an optical grating-based measurement system. This substitution eliminates the need for complex mechanical components and frequency modulation mechanisms, thereby reducing environmental sensitivity while maintaining high measurement accuracy.
2Measurement precision
If a dual-frequency laser interferometer measurement system is used, then multi-DOF displacement measurement capability is achieved, but device complexity and space occupation increase
Solution Approach 1:
The patent merges multiple measurement functions into a single integrated optical grating system. By combining the reference grating, measurement grating, and optical path into one compact interferometer structure, the system achieves multi-DOF measurement capability while reducing overall device complexity and space occupation.
Solution Approach 2:
The optical grating-based system serves multiple measurement functions simultaneously - it can measure displacement, velocity, and acceleration across multiple degrees of freedom using the same basic optical components, thereby reducing system complexity compared to dedicated sensors for each function.
3Measurement precision
If a dual-frequency laser interferometer measurement system is used, then displacement measurement is achieved, but cost increases
Solution Approach 1:
The patent employs cost-effective optical gratings and standard optical components instead of expensive dual-frequency laser sources and complex interferometric arrangements. The use of commercially available green laser pointers and mass-produced grating structures significantly reduces system cost while maintaining sub-nanometer measurement accuracy.
4Measurement precision
If a dual-frequency laser interferometer measurement system is used, then displacement measurement is achieved, but measurement speed improvement becomes difficult and dynamic characteristics measurement capability deteriorates
Solution Approach 1:
The patent uses periodic modulation of the optical path length through controlled movement of the measurement grating, which generates time-varying interference patterns. This periodic action enables high-speed measurement by converting dynamic displacement into frequency-domain signals that can be rapidly processed, thereby improving measurement speed while maintaining accuracy.
Solution Approach 2:
The system is designed to dynamically track rapid changes in grating position by using high-bandwidth photodetectors and real-time signal processing. The optical interference pattern responds instantaneously to grating movement, enabling the system to capture dynamic characteristics such as vibration and acceleration with high temporal resolution.
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 provides high accuracy and low environmental sensitivity, reducing the volume and weight of the workpiece stage while enhancing dynamic performance, enabling precise measurements in ultra-precision applications like semiconductor manufacturing and precision machine tools.
Implementation Method 1
a dual-frequency laser emits dual-frequency orthogonal polarized laser light which is split into transmitted light and reflected light after being incident onto the polarizing beam splitter
Implementation Method 2
after the reference light is incident onto the reference grating, four beams of diffracted and reflected reference light are generated
Implementation Method 3
the measurement principle of the grating measurement system is mainly based on the principle of Moire fringe and the principle of diffraction and interference
Implementation Method 4
the four beams of diffracted and reflected reference light are deflected through the first dioptric element to form four beams of parallel reference light
Data Source
AI summary
A three-DOF (Degree of Freedom) heterodyne grating interferometer displacement measurement system comprises a dual-frequency laser, a grating interferometer, a measurement grating, receivers and an electronic signal processing component; the grating interferometer comprises a polarizing beam splitter, a reference grating and dioptric elements; the measurement system realizes displacement measurement on the basis of grating diffraction, the optical Doppler Effect and the optical beat frequency principle. Three linear displacements can be output by the system when the grating interferometer and the measurement grating perform a three-DOF linear relative motion. The measurement system can reach sub-nanometer and higher resolution and precision, and can simultaneously measure three linear displacements. The measurement system has the advantages of being environmentally insensitive, high in measurement precision, small in size, light in weight, and is capable of improving the overall performances of an ultra-precision stage of a lithography machine as a position measurement system for this stage.