Encoder System for Lithography Positioning Accuracy
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Solution Overview
Problem
In lithography processes for producing micro-devices like liquid crystal display devices, existing exposure apparatuses face challenges in accurately positioning substrates due to air fluctuations, especially as substrate sizes increase, making it difficult to maintain precise positioning across the entire moving range.
Innovation Solution
An exposure apparatus with a measurement system using a grating member and heads that move in orthogonal directions to measure position information, allowing for compensation of measurement errors and precise movement in three degrees of freedom, thereby reducing the influence of air fluctuations and enabling accurate substrate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical interferometer system with a bar mirror is used to obtain position information, then position measurement capability is provided, but air fluctuation influences measurement accuracy
Solution Approach 1:
The patent replaces the optical interferometer system (optical measurement method) with an encoder system (mechanical measurement method). The encoder uses a scale attached to the substrate stage and read heads that mechanically read position information, eliminating the optical path that is susceptible to air fluctuation. This substitution of measurement principle directly resolves the contradiction by removing the harmful optical path while maintaining position measurement capability.
Solution Approach 2:
The patent introduces an encoder scale as an intermediary element between the substrate stage and the measurement system. The scale provides a physical reference that can be read by the encoder heads, serving as a mediator that transfers position information without requiring long optical paths through air. This intermediary mechanism enables accurate position measurement while avoiding the air fluctuation problem.
2Measurement precision
If an encoder system is used to reduce air fluctuation influence, then measurement accuracy improves, but it becomes difficult to cover the entire moving range of large substrates
Solution Approach 1:
The patent divides the encoding function into multiple independent read heads distributed across the substrate stage. Each read head covers a local area, and together they provide comprehensive coverage of the entire substrate moving range. This segmentation allows the encoder system to handle large substrates by distributing measurement responsibilities across multiple heads rather than requiring a single long-scale encoder.
Solution Approach 2:
The patent arranges multiple read heads in a two-dimensional configuration on the substrate stage, extending in directions orthogonal to each other. This spatial distribution in multiple dimensions enables the encoder system to cover the entire moving range of large substrates by positioning heads strategically across the stage area, transforming a one-dimensional scaling problem into a two-dimensional coverage solution.
3Manufacturing precision
If multiple read heads and grating areas are used to measure position in three degrees of freedom, then positioning accuracy improves, but device complexity increases
Solution Approach 1:
The patent designs the encoder system with multiple read heads and grating areas that serve multiple functions simultaneously. The same hardware components (read heads and scales) are used to measure position in multiple degrees of freedom (X, Y, and rotational theta), eliminating the need for separate measurement systems for each degree of freedom. This multi-functionality reduces overall system complexity while achieving three-degree-of-freedom positioning accuracy.
Solution Approach 2:
The patent combines the measurement of multiple degrees of freedom into a unified encoder system. The read heads and grating areas work together in an integrated manner to provide position information for X, Y, and rotational theta simultaneously. By merging these measurement functions into a single coordinated system rather than separate systems, the patent achieves three-degree-of-freedom positioning while managing device complexity.
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 enhances positioning accuracy and reduces the need for costly air-conditioning equipment, allows for smaller and lighter apparatus designs, and simplifies the structure, leading to cost savings and improved maintainability.
Implementation Method 1
a measurement system in which one of a grating member with a plurality of grating areas arranged mutually apart in the first direction and a plurality of first heads each irradiating the grating member with a measurement beam
Implementation Method 2
with each of the plurality of first heads, the measurement beam moves off of one of the plurality of grating areas, and moves to irradiate another grating area adjacent to the one of the plurality of grating areas
Data Source
AI summary
A control system controls a drive system of a substrate holder, based on correction information to compensate for measurement error of a measurement system including an encoder system that occurs due to movement of at least one of a plurality of grating areas (scale), a plurality of heads and a substrate holder, and position information measured by the measurement system, and a measurement beam from a head of each of the plurality of heads moves off from one of the plurality of grating areas and switches to another adjacent grating area, during the movement of the substrate holder in the X-axis direction.