Sub-aperture Figuring Compensation for Anisotropic Crystal Removal
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Solution Overview
Problem
Current sub-aperture figuring processes for optics assume constant material removal rates across optical surfaces, which is invalid for anisotropic crystalline materials, leading to inadequate figure error correction and precision issues, especially for DUV and VUV optics.
Innovation Solution
The method accounts for differential material removal rates by probing crystal fiducials, generating differential removal maps, and modifying the tool influence function to compensate for variations in crystallographic orientations, allowing for more accurate figure error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant material removal rate is assumed in sub-aperture figuring processes, then process simplicity is maintained, but manufacturing precision deteriorates for anisotropic crystalline materials
Solution Approach 1:
The patent applies local quality by determining spatially varying material removal rates across different locations on the optical surface based on crystallographic orientation. Each location has its own removal rate characteristic determined by the local crystal plane orientation relative to the polishing tool motion, allowing precise compensation for anisotropic removal behavior while maintaining a systematic figuring process
Solution Approach 2:
The patent changes the removal rate parameter from a constant value to a spatially varying parameter that depends on crystallographic orientation. By incorporating crystal orientation data and calculating location-specific removal rates, the process adapts to the anisotropic nature of crystalline materials, significantly improving figure error correction precision without excessive complexity
2Manufacturing precision
If polishing tools are restricted to those with minimum differential material removal, then manufacturing precision improves, but device complexity and process flexibility worsen
Solution Approach 1:
The patent changes the approach from restricting tool selection to characterizing and compensating for removal rate variations. By determining the crystallographic orientation and calculating the differential removal rate map, the system can use any polishing slurry or tool while achieving precise figure correction through computational compensation, thereby maintaining manufacturing precision while dramatically improving process flexibility and adaptability
3Manufacturing precision
If differential material removal rates are compensated for, then manufacturing precision improves, but measurement and detection difficulty increases
Solution Approach 1:
The patent applies preliminary action by determining the crystallographic orientation map and calculating the differential material removal rate map before the actual figuring process. This pre-characterization of the workpiece allows the system to compensate for anisotropic removal behavior during figuring, improving manufacturing precision while managing measurement complexity through advance preparation
Solution Approach 2:
The patent introduces a computational model as an intermediary between measurement and figuring. The differential removal rate map serves as a mediator that translates crystal orientation data into compensation factors for the figuring process, reducing the direct complexity of measuring and responding to crystallographic variations in real-time
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 precision and accuracy of sub-aperture figuring processes by compensating for material removal rate variations, improving the ability to create high-precision optical surfaces, particularly for anisotropic crystalline substrates like CaF2 and MgF2.
Implementation Method 1
The rate at which the polishing tool removes material from the optical surface varies, depending on the crystallographic orientation of the optical surface at the point of contact of the polishing tool with the optical surface
Data Source
AI summary
The disclosure relates to methods for compensating for crystal structures differential material removal rates in sub-aperture figuring. A computing machine receives an input related to a substrate crystal structure. The computing machine generates, based on the input, a surface map data capturing the substrate crystal structure. The computing machine generates, based on the surface map data structure, a figuring route data structure for a figuring tool to figure an optical surface on the crystal substrate. The computing machine controls, using the processing circuitry and based on the figuring route data structure, the figuring tool to figure the substrate crystal optical surface.