Structured Polishing Pad for EUV Optical Element Zonal Polishing
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Solution Overview
Problem
In the production of optical elements for microlithography, especially in the EUV range, existing zonal polishing methods face challenges in maintaining a constant removal rate over time while minimizing the introduction of fine structures from the polishing tool, leading to increased tool changes and reduced efficiency in eliminating depth damage and fine structures.
Innovation Solution
The method involves using structured polishing pads adapted to the movement of the polishing tool, such as rotary or eccentric tools, with primary and secondary structuring to ensure a stable supply of polishing agent and uniform lubrication, achieving a constant removal rate and minimizing the introduction of fine structures. The structured pads, featuring spiral shapes or checkered patterns, enhance polishing agent distribution and reduce tool-induced fine structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional zonal polishing methods are used, then material removal can be achieved, but the removal rate varies over time and fine structures are introduced by the polishing tool
Solution Approach 1:
The polishing pad is segmented into multiple zones with different properties: a central polishing zone for material removal and a peripheral lubrication zone for supplying polishing agent. This segmentation allows simultaneous optimization of removal rate and minimization of fine structures by assigning different functions to different regions of the same tool.
Solution Approach 2:
Different regions of the polishing pad are given different local qualities: the central area has higher hardness and polishability for efficient material removal, while the peripheral area has different properties optimized for lubrication and polishing agent supply. This local differentiation resolves the contradiction between high removal rate and fine structure minimization.
2Productivity
If the polishing tool is used for extended periods, then productivity increases, but the removal rate becomes non-constant and tool changes are required
Solution Approach 1:
The polishing pad incorporates a lubrication zone that dynamically supplies polishing agent during the polishing process. This dynamic supply mechanism maintains consistent removal rates over extended periods by adapting to changing conditions during tool use, thereby increasing tool usability without compromising removal rate stability.
3Ease of operation
If polishing agent supply is increased, then lubrication improves, but fine structures from the tool are more prominently introduced
Solution Approach 1:
The polishing pad is divided into a central polishing zone and a peripheral lubrication zone. The lubrication zone specifically supplies polishing agent to improve lubrication, while the central zone focuses on material removal. This segmentation allows adequate lubrication without excessive polishing agent that would otherwise introduce more fine structures.
Solution Approach 2:
The lubrication zone acts as an intermediary between the polishing agent supply system and the workpiece. It controls and regulates the supply of polishing agent, providing sufficient lubrication while preventing excessive agent that would cause prominent fine structures from the tool.
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 allows for a constant removal rate over extended periods, reducing tool changes and minimizing fine structures on the workpiece, thereby improving the efficiency of the polishing process and extending tool usability, while effectively eliminating depth damage and fine structures.
Implementation Method 1
The structuring of the polishing pad is adapted to the movement of the polishing tool in a material-removing manner over a surface to be polished of the workpiece. The structure of the polishing pad, which is adapted to the movement of the tool, is intended to enable a stable supply of polishing agent between tool surface and workpiece surface and 'good lubrication' associated therewith.
Data Source
AI summary
A method for the zonal polishing of a workpiece includes using a polishing tool to guide a structured polishing pad over the surface of workpiece to remove material from the workpiece. A structured polishing pad includes a structuring adapted to the movement of a polishing tool.