Wafer Stage Density Distribution for Weight Reduction
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Solution Overview
Problem
Existing stage apparatuses for photolithography processes face challenges in achieving weight reduction while maintaining high rigidity, strength, and flatness, particularly in scanning exposure-type projection exposure apparatuses, where thin moving members are required to reduce weight and enhance speed, but manufacturing difficulties and increased costs are encountered due to the inverse relationship between member thickness and bending rigidity and buckling strength.
Innovation Solution
The use of materials with non-uniform density distribution, where higher density is applied to areas requiring high rigidity and flatness and lower density to areas that do not, such as in the reticle and wafer stages, allowing for weight reduction without compromising essential characteristics, exemplified by the use of porous ceramics and sintered metals in components like mirrors and stage bodies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If moving members are made thin to reduce weight, then weight is reduced and speed is improved, but bending rigidity and buckling strength fall by a large extent
Solution Approach 1:
The patent applies local quality by creating non-uniform density distribution within the moving members, where different regions have different material densities optimized for their specific functional requirements. This allows thin structures to maintain sufficient strength in critical areas while reducing overall weight.
Solution Approach 2:
The patent employs composite materials with varying density characteristics, combining materials of different densities in a single moving member structure. This enables the integration of high-strength regions and low-weight regions within the same component, resolving the contradiction between weight reduction and strength maintenance.
2Weight of moving object
If materials with low density are used to maintain rigidity and strength, then weight is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies parameter changes by modifying the density parameter of materials within the moving members rather than changing the fundamental material type. This allows for weight reduction through controlled density variation (e.g., using porous or graded materials) while maintaining compatibility with existing manufacturing processes, thus avoiding excessive manufacturing complexity.
3Reliability
If large and heavy mirrors are employed in the projection optical system, then optical performance is improved, but apparatus weight increases
Solution Approach 1:
The patent applies local quality to mirror structures by creating non-uniform density distribution, particularly in the substrate and support structures. Critical optical surfaces maintain high density for precision and stability, while non-critical regions use lower density materials to reduce overall weight without compromising optical performance.
Data Source
AI summary
A wafer stage system moves a wafer stage that retains a wafer via a wafer holder along a wafer base. For example, the wafer holder is formed from a material whose density is not uniform, such that the portion that includes the reflecting surface that reflects a measuring beam for position measurement is a high-density portion, and the other portions are low-density portions. Or, the wafer stage is formed from a material whose density is not uniform, such that the portion that includes the surface that constitutes a gas bearing is a high-density portion, and the other portions are low-density portions.