Encoder Head Common-Path Optical Design for Precision Alignment
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Solution Overview
Problem
Current exposure apparatus in semiconductor processing face challenges in reducing cost and complexity while achieving precise positioning of reticles and wafers, particularly in the interference and alignment of measurement and reference beams.
Innovation Solution
The use of encoders with measurement and reference beams that propagate through a common set of optical elements, utilizing corner cubes and Risley prisms to minimize angular differences and ensure accurate displacement measurements, allowing for improved precision and reduced cyclic nonlinear errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If measurement and reference beams are separated into different optical paths, then alignment flexibility is improved, but alignment errors and cyclic nonlinear errors increase
Solution Approach 1:
The patent merges the measurement beam and reference beam into a common optical path where they share the same optical elements. This is achieved by directing both beams through the same objective lens and other optical components, ensuring they experience identical optical conditions. The beams are separated only at the detection stage, allowing them to maintain common-path propagation that eliminates differential optical errors while preserving alignment flexibility.
2Measurement precision
If complex optical elements are used to separate and control beams, then beam control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs the objective lens to perform multiple functions simultaneously - it serves as both the imaging lens for the measurement beam and a optical element for the reference beam. The same optical components that are necessary for the measurement function also serve to control and shape the reference beam, eliminating the need for separate dedicated optical elements and reducing overall system complexity.
Solution Approach 2:
Optical elements in the system are designed to serve multiple purposes. The objective lens and other optical components handle both measurement and reference beams, performing multiple functions within a single component rather than requiring separate specialized elements for each beam type, thereby reducing device complexity and cost.
3Manufacturing precision
If additional optical elements are introduced to correct beam paths, then positioning accuracy is improved, but introduction of additional angular differences and errors increases
Solution Approach 1:
By keeping the measurement and reference beams in a common optical path, the patent ensures that both beams pass through the exact same optical elements in sequence. This eliminates the problem of additional angular differences that would arise from introducing separate correction elements for each beam, as no such elements are needed - the common path itself provides the correction.
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 efficiency of semiconductor processing by reducing alignment errors and cyclic nonlinear errors, while maintaining a cost-effective and simplified optical system design.
Implementation Method 1
corner cubes (solid or air) or other retroreflectors are situated to define first and second portions of an optical path so as to reduce introduction of additional angular differences between measurement and reference beams
Implementation Method 2
deliver the measurement beam to a grating situated at a target, and combine a diffracted portion of the measurement beam and the reference beam
Implementation Method 3
combine a diffracted portion of the measurement beam and the reference beam at an optical system output
Data Source
AI summary
Encoder systems provide measurement and reference optical paths based on propagation in a common set of optical elements along paths that are displaced angularly or spatially. Associated measurement and reference beams are reflected by corner cubes to as to define first paths and second paths. The measurement and reference beams are combined to determine a work piece displacement in a manufacturing process.