Combined Encoder Interferometer Unit for Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithographic apparatuses face conflicting requirements of high scanning speed and increasing wafer diameter, which necessitate a balance between low mass and larger substrate table size, while existing position measurement systems increase the weight and size of the substrate table, leading to measurement errors and calibration challenges.
Innovation Solution
A compact position measurement unit combining a diffraction type encoder and an interferometer, which determines positions in multiple dimensions using a combined optical unit, reducing the space and weight requirements on the substrate table and enabling higher accuracy and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate interferometers and encoders are used for position measurement in different dimensions, then measurement precision is improved, but device complexity and weight increase
Solution Approach 1:
The patent combines the encoder and interferometer into a single integrated measurement unit. The encoder measures position in the scanning direction (X-dimension) while the interferometer measures position in the vertical direction (Z-dimension), both within the same optical path. This merging reduces the number of separate measurement units from 6 to 3, thereby reducing device complexity while maintaining measurement precision in all required dimensions.
2Measurement precision
If multiple separate measurement units are applied for six degrees of freedom measurement, then measurement precision is improved, but weight of substrate table increases
Solution Approach 1:
The patent integrates encoder and interferometer measurements into a single measurement unit that attaches to the substrate table. By combining the optical paths and using a unified detector system, the weight added to the substrate table is minimized compared to using six separate measurement units. The integrated design reduces redundant components while maintaining the capability to measure all six degrees of freedom with high precision.
3Measurement precision
If separate measurement units are used for each dimension, then measurement precision is improved, but area on substrate table surface increases
Solution Approach 1:
The patent consolidates the encoder grating and interferometer optical paths into a compact integrated unit. The encoder grating can be positioned close to the substrate table surface, and the interferometer uses the same optical path for both X and Z dimension measurements. This merging reduces the total surface area required on the substrate table compared to having separate measurement units for each dimension, while maintaining high measurement precision through the combined optical system.
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 combined optical unit allows for precise position measurement in six degrees of freedom with reduced size and weight, enhancing the balance between scanning speed and wafer size, leading to higher accelerations and accuracy, and reducing the size and mass of the substrate table.
Implementation Method 1
a diffraction type encoder to determine by means of a diffraction of an encoder measurement beam on a first and a second diffraction grating the position in the first dimension
Implementation Method 2
an interferometer to determine by means of an interference between an interferometer measurement beam following a reference path and a measurement path respectively, the position in the second dimension
Data Source
AI summary
A measurement unit to determine a position in a first and second dimension includes a diffraction type encoder and an interferometer. The diffraction type encoder determines by means of a diffraction on a first and a second diffraction grating the position in the first dimension of the second grating with respect to the first grating, The interferometer determines the position in the second dimension of a mirror. The measurement unit includes a combined optical unit to transfer an encoder measurement beam as well as an interferometer measurement beam. Further, the measurement unit may include a combined light source for the encoder as well as the interferometer. One of the first and second diffraction gratings may further show some degree of zero order reflection to provide the mirror of the interferometer.