Birefringent Lens Encoder Head for Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional encoder heads for lithographic exposure tools are structurally complex, require multiple optical components, and have tight operational tolerances, making them costly and difficult to align, while also limiting the size and efficiency of the measurement system.
Innovation Solution
A compact encoder head design using a single optically-isotropic optical block combined with a birefringent lens element, which reduces the number of optical components and aligns them more simply, allowing for increased beam size and reduced stray noise, while preventing parallel stray beams and minimizing geometric errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional encoder heads use multiple optical components to achieve precise position measurement, then measurement precision is improved, but device complexity increases and alignment difficulty worsens
Solution Approach 1:
The patent combines multiple optical components (isotropic optical block, birefringent lens, and retroreflector) into a single integrated encoder head assembly. This merging reduces the number of separate components that require alignment while maintaining the functional complexity needed for high-precision measurement through the coordinated interaction of these integrated elements
Solution Approach 2:
The encoder head design makes the optical system multi-functional by integrating components that simultaneously perform multiple functions: the isotropic block provides beam splitting and retroreflection, the birefringent lens provides focal length control and polarization manipulation, and the retroreflector provides beam redirection. This multi-functionality reduces the need for separate dedicated components for each function
2Measurement precision
If conventional encoder heads use multiple optical components to achieve precise position measurement, then measurement precision is improved, but ease of operation worsens due to alignment challenges
Solution Approach 1:
The optical components are pre-aligned and integrated into a unified encoder head assembly during manufacturing. The isotropic block, birefringent lens, and retroreflector are positioned relative to each other in their final operational configurations before being installed in the exposure tool, eliminating the need for complex field alignment procedures
3Measurement precision
If conventional encoder heads use multiple optical components then measurement precision is improved, but the size of the measurement system increases
Solution Approach 1:
The encoder head design nests optical components within each other to minimize overall volume. The retroreflector is positioned at or near the focal point of the birefringent lens, and the isotropic block is integrated into the same housing, creating a compact nested arrangement where components occupy overlapping or adjacent spatial volumes rather than requiring separate dedicated spaces
4Measurement precision
If conventional encoder heads use multiple optical components then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent integrates multiple optical components into a single manufactured assembly, reducing the number of separate manufacturing processes, quality control steps, and assembly operations required. This merging reduces manufacturing complexity and cost while maintaining the precision measurement capabilities through the coordinated function of the integrated components
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 design enhances the accuracy and efficiency of position measurement in lithographic exposure tools by reducing structural complexity, alignment challenges, and size limitations, while maintaining high light efficiency and minimizing cyclic non-linear errors.
Implementation Method 1
a lens, said lens containing at least one birefringent lens element
Implementation Method 2
a birefringent plane-parallel plate configured to maintain a vector of polarization of light, incident onto said plate perpendicularly to a surface of the plate, upon transmission of such light through said birefringent plane-parallel plate while, at the same time, to change a vector of polarization of light incident onto said surface obliquely
Implementation Method 3
an optical surface disposed in optical communication with said cuboid to form a first beam of light by redirecting a portion of an input beam of light
Data Source
AI summary
An encoder head configured for use with a lithographic exposure tool. The head is devoid of the multiplicity of optical corner-cubes and includes, instead, a single, geometrically substantially perfect cuboid of optically-isotropic material complemented, in operation, with a birefringent lens to form a contraption that, as a unit, splits a single beam of light delivered to the contraption into four measurement (sub-)beams of light (two in xz-plane, two in yz-plane) and causes each of measurement sub-beams to interact with the wafer-stage diffraction grating at the same location twice: upon the first pass by the grating and upon the second pass by the grating. The use of the contraption solves problems of (i) structural complexity of a conventional encoder head for use in an exposure tool, (ii) burdensome alignment of the multitude of optical prisms in the process of forming such encoder head, and (iii) cyclic non-linear errors associated with measurements involving conventional corner-cubes-based encoder heads while, at the same time, reducing the geometrical footprint of the encoder head. The contraption is complemented with a birefringent prismatic element positioned across the axis of the contraption between the cuboid and the birefringent lens.