Dual Encoder Position Measurement for Lithography Stage Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In the lithography process for manufacturing semiconductor devices, existing exposure apparatuses face challenges in achieving high precision position control due to temperature fluctuations and background vibrations, which affect the accuracy of position measurement systems, particularly with larger wafers where measurement arm vibrations become significant, and the temporal drift of grating pitch in encoder systems.
Innovation Solution
The exposure apparatus employs a dual measurement system with a first measurement system irradiating a measurement beam onto a grating on the rear surface of a wafer table and a second measurement system with heads on the frame member, providing redundant position information to enhance measurement reliability and reduce errors, allowing for precise position control of the moving member within a predetermined range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser interferometer is used to measure the position of the wafer stage, then position measurement is achieved, but measurement accuracy deteriorates due to temperature change and air fluctuation on the beam path
Solution Approach 1:
The patent replaces the laser interferometer (optical measurement system) with an encoder system that uses a grating and magnetic fields for position measurement. The encoder measures position by detecting changes in magnetic field distribution as the wafer table moves, eliminating the need for laser beams that are sensitive to temperature and air fluctuations. This substitution of measurement mechanism resolves the contradiction by achieving position measurement without being affected by thermal and atmospheric conditions.
Solution Approach 2:
The patent introduces a grating with magnetic markers as an intermediary element between the wafer table and the measurement system. The grating remains fixed relative to the wafer table while the measurement head detects its position through magnetic field changes. This intermediary allows indirect measurement that is insensitive to environmental factors, resolving the contradiction between achieving accurate measurement and avoiding temperature/air fluctuation influences.
2Area of stationary object
If an encoder system with a long measurement arm is used for larger wafers, then measurement range is increased, but measurement accuracy deteriorates due to vibration of the measurement arm
Solution Approach 1:
The patent inverts the traditional encoder configuration by placing the grating on the moving wafer table and the measurement head on the stationary frame, rather than the conventional arrangement. This inversion allows the measurement head to remain stationary and stable, eliminating vibrations from a long measurement arm while still accommodating large wafer tables. The grating moves with the wafer table, and the stationary measurement head detects its position through magnetic field changes, resolving the contradiction between large measurement range and measurement accuracy.
Solution Approach 2:
The patent extracts the measurement function from a long, vibration-prone measurement arm and concentrates it in a compact, stationary measurement head. By placing the measurement head on the frame rather than extending it via a long arm, the system eliminates the source of vibration while maintaining the ability to measure positions across large wafer tables. This extraction of the measurement function from the extended structure resolves the contradiction between measurement range and precision.
3Measurement precision
If the grating pitch is made smaller to achieve higher position measurement resolution, then measurement resolution is improved, but measurement reliability deteriorates due to temporal drift of the grating pitch
Solution Approach 1:
The patent employs a composite structure combining magnetic markers embedded in the grating with a magnetic field-based detection system. The magnetic markers serve as stable reference points that do not suffer from thermal expansion or mechanical drift affecting the grating pitch. By combining the grating structure with magnetic field detection, the system achieves high resolution measurement while maintaining reliability, as the magnetic field distribution around the markers remains stable even when the grating pitch changes due to temperature or other environmental factors.
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
This dual measurement approach enables constant high-precision positioning of the moving member by combining reliable position information from both systems, effectively mitigating the impact of temperature fluctuations and vibrations, and maintaining accuracy even with larger wafers.
Implementation Method 1
a first measurement system which measures a first position information of the moving-member by irradiating a first measurement beam from below on the first grating and receiving light from the first grating of the first measurement beam
Implementation Method 2
irradiating a first measurement beam from below on the first grating and receiving light from the first grating of the first measurement beam
Data Source
AI summary
An exposure apparatus is equipped with a table which holds a wafer and is movable along an XY plane and has a grating provided on its rear surface, an encoder which irradiates a first measurement beam on the grating from below, receives a return light, and measures a first position information of the table when the table moves in a predetermined range, and another encoder which has a head section provided in a frame and irradiates a second measurement beam on a different grating on the table from the head section, receives a return light, and can measure a second position information of the table, concurrently with measurement of the first position information by the encoder when the table moves in predetermined range. A controller drives the table, based on position information having a higher reliability of the first and the second position information.