Lithographic Mask With Overhanging Shield For Peripheral Exposure Control
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Solution Overview
Problem
Lithographic apparatuses face contamination issues due to debris falling on the photosensitive surface during mask loading, which can lead to exposure of unintended peripheral regions, compromising the cleanliness and accuracy of the exposure process.
Innovation Solution
A substrate table with a moveable mask, such as a ring with a concave edge, is used to prevent exposure of peripheral regions by being positioned to overhang and shield these areas from the radiation beam, allowing for controlled movement to avoid contamination during substrate loading and exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mask is used to block radiation and form exposure exclusion regions, then the peripheral exposure region can be prevented from being exposed, but the mask passes over the underlying wafer during loading, causing debris to fall onto the photosensitive surface and contaminate it
Solution Approach 1:
The mask is extended in the vertical dimension to create an overhanging structure that shields the peripheral region while allowing the mask to be loaded without passing directly over the substrate. The mask comprises a base portion and an overhanging portion that extends beyond the base portion in a direction perpendicular to the substrate, creating a three-dimensional shielding structure that prevents both exposure and contamination.
Solution Approach 2:
The mask is positioned in advance to overhang the peripheral exposure exclusion region before the exposure process begins. This preliminary positioning ensures that the peripheral region is shielded from radiation during exposure, and the overhanging structure is already in place to prevent debris contamination during subsequent mask loading operations.
2Manufacturing precision
If the mask is positioned to overhang the peripheral exposure region to prevent exposure, then exposure precision is improved, but the mask structure becomes more complex
Solution Approach 1:
The mask is divided into two functional segments: a base portion that provides structural support and positioning, and an overhanging portion that provides the shielding function. This segmentation allows each part to be optimized independently - the base portion for stable mounting and the overhanging portion for effective radiation blocking and debris prevention.
Solution Approach 2:
The mask structure transitions from a traditional two-dimensional planar design to a three-dimensional structure with vertical extension. The overhanging portion extends beyond the base portion in the vertical dimension, creating a shield that effectively blocks radiation and prevents debris contamination without requiring complex lateral mechanisms.
3Manufacturing precision
If the mask is made opaque to block radiation, then exposure control is improved, but the mask material selection becomes more limited
Solution Approach 1:
The optical properties of the mask material are adjusted by changing its physical parameters - specifically, applying a coating layer with appropriate thickness and composition to achieve the desired opacity. This allows the base material to be selected for mechanical properties (strength, thermal stability) while the coating provides the required radiation blocking capability, expanding material selection flexibility.
Solution Approach 2:
The mask employs a composite structure consisting of a base material and an opaque coating layer. This composite approach allows optimization of different properties in different layers - the base material provides structural integrity and thermal stability, while the coating layer provides radiation blocking. This enables adaptation to different radiation wavelengths and exposure conditions.
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 solution effectively prevents exposure of peripheral regions, maintaining the cleanliness and accuracy of the exposure process by ensuring the mask does not directly pass over the substrate during loading and exposure, thereby reducing contamination and improving the precision of the lithographic process.
Implementation Method 1
The mask is arranged to overhang a predetermined exposure exclusion region of a photosensitive surface of a wafer. The mask is positioned over the wafer prior to exposure of the wafer, thereby shielding the regions of the photosensitive surface underlying the mask.
Data Source
AI summary
A substrate table for a lithographic apparatus includes a mask constructed and arranged to prevent exposure of a peripheral exposure region of a substrate on the substrate table. The mask is attached to a moveable carrier. The moveable carrier has a range of movement which at least partially circumnavigates the substrate table.