Microlithography Projection Optics Real-Time Position Correction
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Solution Overview
Problem
Conventional projection exposure systems for microlithography suffer from image smearing due to drift in image position during exposure, particularly in EUV systems, leading to overlay errors and requiring stringent mechanical stability, which is costly and difficult to achieve with materials of low thermal expansion.
Innovation Solution
A projection exposure system with a measurement structure and detector that simultaneously image the mask structures and a measurement structure using the same projection optics, allowing for real-time establishment and correction of lateral image position, thereby preventing smearing and improving imaging stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional projection exposure systems use standard materials for the projection objective structure, then manufacturing cost is reduced and ease of manufacture is improved, but mechanical stability and image position stability deteriorate due to thermal expansion
Solution Approach 1:
The patent introduces a measurement structure and detector as intermediary elements to monitor image position drift in real-time. The measurement structure is imaged onto the detector simultaneously with the mask structures, allowing continuous detection of positional deviations without interrupting the exposure process. This mediator approach enables active compensation for thermal expansion effects.
Solution Approach 2:
The system implements feedback control by continuously measuring the lateral position of the measurement structure image on the detector and using this information to adjust the mask holding device or projection optics. The evaluation device processes the detector signals to determine image position deviations, which are then fed back to correct the positioning, creating a closed-loop system that compensates for thermal drift.
2Measurement precision
If the exposure process is interrupted for control measurements to monitor image position, then measurement precision is improved, but productivity deteriorates due to exposure time loss
Solution Approach 1:
The patent merges the measurement function with the exposure function by using the same projection optics to image both the mask structures and the measurement structure simultaneously. The measurement structure is positioned in the mask plane or substrate plane such that its image is formed on the detector during the exposure process, combining two functions into one operation.
Solution Approach 2:
The system maintains continuous useful action by performing measurement and exposure operations concurrently without interruption. The measurement structure image is captured on the detector throughout the exposure process, allowing real-time monitoring of image position stability without stopping the exposure, thus maintaining both measurement precision and productivity.
3Stability of the object's composition
If materials with extremely low thermal expansion coefficients are used for the projection objective structure, then mechanical stability is improved, but cost and processing difficulty worsen
Solution Approach 1:
The patent replaces the mechanical approach of using specialized low thermal expansion materials with an optical measurement and control system. Instead of relying on the mechanical stability of exotic materials like Invar or Ultralight, the system uses optical measurement (imaging the measurement structure) and electronic control to achieve the required stability, substituting mechanical solutions with optoelectronic ones.
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 system effectively prevents smearing of the latent image in the photoresist by continuously monitoring and correcting the lateral image position during exposure, enhancing the mechanical stability and image quality, especially in EUV systems.
Implementation Method 1
projection optics for imaging the mask structures onto the substrate during an exposure process, a measurement structure which is disposed in a defined position with respect to a reference element of the projection exposure system, which defined position is mechanically uncoupled from the position of the mask holding device, a detector arranged for recording an image of the measurement structure produced by imaging of the latter using the projection optics
Data Source
AI summary
A projection exposure system (10) for microlithography which includes: a mask holding device (14) holding a mask (18) with mask structures (20) disposed on the mask, a substrate holding device (36) holding a substrate (30), projection optics (26) imaging the mask structures (20) onto the substrate (30) during an exposure process, and a measurement structure (48) disposed in a defined position with respect to a reference element (16) of the projection exposure system (10), which defined position is mechanically uncoupled from the position of the mask holding to device (14). The projection exposure system (10) also includes a detector (52) arranged to record an image of the measurement structure (48) imaged by the projection optics (26). The projection exposure system (10) is configured such that during operation of the projection exposure system (10) the imaging of the mask structures (20) and the imaging of the measurement structure (48) take place at the same time by the projection optics (26. An evaluation device (54) is configured to establish a lateral position of the image of the measurement structure (48) in the area of the detector (52) during the exposure process.