Microlithography Illumination System Using Spatial Light Modulator
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Solution Overview
Problem
Current microlithographic projection exposure systems lack flexibility in varying both angular and spatial irradiance distributions in the mask plane, requiring complex and costly mirror arrays with numerous control systems to achieve desired illumination settings.
Innovation Solution
An illumination system incorporating an optical raster plate with a spatial light modulator that produces light spots with periodic irradiance distributions, allowing for flexible control of light spot positions and combinations to achieve varied angular and spatial irradiance distributions by overlapping spots with specific displacements and orientations, utilizing a control unit to adjust the spatial light modulator and optionally including a condenser for Fourier transformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mirror array with numerous individually controllable micromirrors is used to achieve flexible angular and spatial irradiance distributions, then the adaptability and versatility of the illumination system is improved, but the device complexity and manufacturing cost increase significantly
Solution Approach 1:
The illumination system is segmented into multiple independent light sources, where each light source corresponds to a specific angular irradiance distribution. This allows selective activation of individual light sources to achieve different illumination settings without requiring complex control of numerous micromirrors.
Solution Approach 2:
Each light source is designed to provide a specific angular irradiance distribution that can serve multiple patterning needs. The same light source can be used for different patterns by adjusting its position and orientation, reducing the need for a large number of individually controllable elements.
2Device complexity
If conventional illumination systems are used, then the device complexity is kept low, but the adaptability to produce different angular and spatial irradiance distributions for various patterns is limited
Solution Approach 1:
The system enables easy adaptation to different patterns by changing parameters such as the position, orientation, and activation state of individual light sources. This allows flexible adjustment of angular and spatial irradiance distributions without modifying the physical structure of the illumination system.
3Manufacturing precision
If light spots with periodic irradiance distributions are produced on the optical raster plate, then the manufacturing precision of the illumination pattern is improved, but the device complexity increases due to the spatial light modulator
Solution Approach 1:
The optical raster plate acts as an intermediary element that receives light from the spatial light modulator and transfers the periodic irradiance distribution pattern to the mask plane. This intermediary structure simplifies the overall system by providing a fixed optical path and pattern transfer mechanism.
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
Enables flexible and efficient generation of various irradiance distributions in the mask plane without significant light loss, allowing for precise adaptation to different patterns and improved imaging accuracy, reducing system complexity and cost.
Implementation Method 1
a spatial light modulator which is configured to produce on the light entrance surface of the optical raster plate a plurality of light spots and configured to vary the position of the light spots on the light entrance surface in response to a command signal received from the control unit
Implementation Method 2
an optical raster plate which has a light entrance surface... an irradiance distribution on the light entrance surface determines an angular light distribution of projection light when it impinges on a mask to be illuminated
Data Source
AI summary
An illumination system of a microlithographic projection exposure apparatus comprises an optical raster plate having a light entrance surface. An irradiance distribution on the light entrance surface determines an angular light distribution of projection light when it impinges on a mask to be illuminated. The illumination system further comprises a control unit and a spatial light modulator which produces on the light entrance surface of the optical raster plate a plurality of light spots whose positions can be varied. At least some of the light spots have, along a reference direction (X), a spatial irradiance distribution comprising a portion in which the irradiance varies periodically with a spatial period P.