Wavelength-Filter Illumination Control for Exposure Apparatus
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Solution Overview
Problem
Existing exposure apparatuses struggle to maintain constant illuminance due to changes in the light emission spectrum of mercury lamps, especially when switching wavelength filters, leading to inaccuracies in power adjustment.
Innovation Solution
The exposure apparatus includes a control unit that uses specific correction values for different wavelength filters to adjust input power, ensuring constant illuminance by measuring and applying appropriate approximation coefficients for each filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a wavelength filter with a narrow band is used, then chromatic aberration is reduced and image performance is improved, but the amount of combined light decreases and illuminance is reduced
Solution Approach 1:
The patent changes the parameter of wavelength band selection by providing multiple wavelength filters with different bandwidths (narrow band and broad band). The system can switch between these filters depending on the exposure requirements, allowing optimization between image performance and illuminance for different process conditions.
2Illumination intensity
If a wavelength filter with a broad band is used, then the amount of combined light increases and illuminance is improved, but chromatic aberration increases and image performance deteriorates
Solution Approach 1:
The system provides multiple wavelength filters with different bandwidth parameters. By switching between narrow band filters (for high image performance) and broad band filters (for high illuminance), the system can adapt to different exposure requirements without being constrained by a single filter's limitations.
3Device complexity
If a single approximation coefficient is used for constant illuminance control, then the function is simple to implement, but accuracy deteriorates when wavelength filters are switched
Solution Approach 1:
The patent segments the approximation coefficient into multiple coefficients, each corresponding to a specific wavelength filter. When a wavelength filter is switched, the system selects the appropriate approximation coefficient for that filter, ensuring accurate constant illuminance control for each filter without requiring a complex unified model.
Solution Approach 2:
The system creates separate approximation coefficients for each wavelength filter, essentially copying the constant illuminance control function for each filter type. This allows each filter to have its own optimized control parameters, maintaining accuracy across filter switches.
4Adaptability or versatility
If multiple wavelength filters are mounted for process versatility, then adaptability is improved, but the constant illuminance function becomes inaccurate when filters are switched
Solution Approach 1:
The system segments the control parameters by creating separate approximation coefficients for each wavelength filter. This segmentation allows the system to maintain multiple filters for process versatility while ensuring that each filter has its own accurate control parameters, preventing the accuracy deterioration that would occur with a single universal coefficient.
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 approach allows for precise maintenance of constant illuminance across varying wavelength filters, improving image quality and process accuracy in lithography processes.
Implementation Method 1
By changing input power of the mercury lamp, it is possible to change an optical output of the mercury lamp
Implementation Method 2
A wavelength filter is used as an optical element that passes only a specific wavelength band
Implementation Method 3
a control unit configured to control input power to the light source using a correction value corresponding to a relation of a change in illuminance to the input power
Data Source
AI summary
An exposure apparatus includes: an illumination optical system including a plurality of optical elements changing a wavelength band of light from a light source and configured to illuminate an illuminated surface with light of which a wavelength band has been changed by one of the plurality of optical elements; and a control unit configured to control input power to the light source using a correction value corresponding to a relation of a change in illuminance to the input power to the light source to maintain constant illuminance on the illuminated surface. The control unit uses different correction values for the plurality of optical elements.