Edge Mask Radial Concave Design for Lithography
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Solution Overview
Problem
Existing lithographic apparatuses face challenges in preventing exposure of peripheral substrate portions while maintaining cleanliness and minimizing cycle time, as they often require large mask movements and risk contamination due to added mass and complexity.
Innovation Solution
A lithographic apparatus with a substrate table and projection system that uses an edge mask with a radial concave edge, attached to a mask carrier with tangential and radial drive mechanisms, allowing precise adjustment to prevent peripheral exposure without hindering substrate movement, and is designed to minimize contamination risks by being independent of the substrate table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a ring-shaped mask is transferred above and across the width of the substrate to prevent peripheral exposure, then the peripheral exposure is prevented, but the mask requires large movement relative to the substrate which increases operation time and creates time constraints
Solution Approach 1:
The patent extracts the mask from the substrate table and attaches it to the reticle instead. This eliminates the need for large mask movements across the substrate, as the mask moves with the reticle which has smaller, more controlled movements. The mask function is separated from the substrate handling system, resolving the time constraint issue.
Solution Approach 2:
The mask is merged with the reticle assembly, moving together as a single unit. This combining eliminates the need for independent mask positioning mechanisms and reduces the overall complexity of the system. The mask and reticle are positioned and moved together, reducing operation time while maintaining peripheral exposure prevention.
2Manufacturing precision
If a mask is transferred across the substrate to prevent peripheral exposure, then the exposure is prevented, but there is always a risk of contamination of the substrate from dust or other particles falling from the mask
Solution Approach 1:
The mask is extracted from the substrate environment and attached to the reticle instead. This separation eliminates the risk of mask-related contamination to the substrate, as the mask no longer moves over or near the substrate during exposure. The harmful factor of contamination is removed by changing the mask's reference frame from substrate-based to reticle-based.
3Reliability
If a ring-shaped mask or diaphragm arrangement is positioned proximal to the reticle, then the mask can move with the reticle, but the ring needs to be bigger and requires larger strokes of movement which may negatively impact cycle time
Solution Approach 1:
Instead of making the mask larger to cover the substrate when moving with the reticle, the patent inverts the approach by using a smaller mask that only needs to cover the peripheral region. The mask is strategically positioned to block only the necessary peripheral exposure areas, reducing the movement stroke required while maintaining effectiveness.
4Measurement precision
If a mask support with drive mechanism is connected to the substrate table to adjust mask position, then the mask position can be controlled, but the added mass of the mask and drive mechanism negatively impacts movement of the substrate table
Solution Approach 1:
The mask support and drive mechanism are extracted from the substrate table and transferred to the reticle assembly. This eliminates the added mass from the substrate table, improving its movement performance. The mask positioning function is relocated to where it is needed (the reticle side) without burdening the substrate table.
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 effectively prevents peripheral exposure with minimal impact on cycle time and maintains substrate cleanliness by allowing the edge mask to be accurately positioned within the radiation beam, reducing the need for large mask movements and minimizing contamination risks through independent operation from the substrate table.
Implementation Method 1
The edge mask is constructed and arranged to cause a projected shadow in the peripheral portion when the edge mask is inserted into the beam of radiation
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A lithographic apparatus (10) and method for preventing exposure of a peripheral portion (P) of a substrate (S). An edge mask (M) has a radial concave edge (E) that extends over less than half a circle arch. The edge mask (M) is connected to a mask carrier (4) that circumnavigates the projection system (2) to adjust a tangential coordinate (Φ) and a radial coordinate (R) of the edge mask (M) with respect to the optical axis (A) of the projection system (2) for inserting the edge mask (M) at a variable distance into the beam of radiation (B). The tangential and radial positions (Φ,R) of the edge mask (M) are coordinated with a changing position (X,Y) of the substrate (S) to prevent exposure of the peripheral portion (P) of the substrate (S) during exposure of the target region (T).