Lithographic Apparatus Focal Plane Alignment for Multi-Level Substrates
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Solution Overview
Problem
Lithographic apparatuses face challenges in accurately patterning substrates with features at different heights due to the narrow depth of focus, limiting the critical dimension and accuracy of patterned features, especially when the height variation exceeds the focal depth of the projection system.
Innovation Solution
A method and apparatus that involve determining the relative heights of planar surfaces on a substrate and adjusting the substrate table in a direction parallel to the beam axis to align the focal plane with each surface, ensuring precise projection of a patterned beam onto surfaces at varying heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the substrate is exposed at a fixed height with the focal plane aligned with the main surface, then the exposure process is simple and fast, but features on surfaces at different heights fall outside the focal depth, limiting patterning accuracy
Solution Approach 1:
The substrate table is made dynamically adjustable in the vertical direction (Z-axis) to change its height relative to the projection system. This allows the focal plane to be dynamically aligned with different surface heights on the substrate, enabling accurate patterning of features at varying elevations while maintaining a relatively simple exposure process
Solution Approach 2:
A height measurement device measures the actual height of different surfaces on the substrate, and this measurement information is used to control the vertical position of the substrate table. This feedback mechanism ensures that the substrate table is positioned at the correct height for each surface, achieving precise focal plane alignment without requiring complex manual adjustment procedures
2Adaptability or versatility
If the depth of focus is increased to accommodate surfaces at different heights, then all surfaces can be exposed simultaneously, but the critical dimension of patterned features deteriorates
Solution Approach 1:
Instead of increasing the depth of focus to accommodate all surface heights, the system dynamically adjusts the substrate table height to bring each surface into the narrow focal plane sequentially. This maintains the narrow depth of focus required for high critical dimension precision while adapting to surfaces at different heights through vertical positioning changes
Solution Approach 2:
The solution moves from attempting to accommodate height variations within the optical dimension (depth of focus) to resolving height differences through a positional dimension (vertical substrate table movement). By changing the problem from optical accommodation to mechanical positioning, the system maintains narrow depth of focus for high precision while handling multi-level surfaces
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 enhances the accuracy and precision of patterning features on substrates with multiple levels, allowing for the creation of features with smaller critical dimensions by maintaining the focal plane alignment with each surface, thereby overcoming the limitations of the depth of focus.
Implementation Method 1
projecting a patterned beam of radiation onto the target region of the substrate such that the focal plane of the beam substantially coincides with the plane of one of the generally planar surfaces
Data Source
AI summary
A device manufacturing method is disclosed that includes providing a substrate on a substrate table, the substrate having a target region comprising a plurality of generally planar surfaces, each surface having a different height relative to the substrate table, determining the relative heights of each generally planar surface, projecting a patterned beam of radiation onto the target region of the substrate such that the focal plane of the beam substantially coincides with the plane of one of the generally planar surfaces, moving the substrate table in a direction substantially parallel to the axis of the beam, and projecting the patterned beam of radiation onto the target region of the substrate such that the focal plane of the beam substantially coincides with the plane of another of the generally planar surfaces.