Synthetic Quartz Substrate Flatness Design for EUVL
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Solution Overview
Problem
Current methods for producing synthetic quartz glass substrates with high flatness, low defect density, and minimal surface roughness are inefficient, leading to increased processing costs and time, and are not suitable for extreme ultraviolet lithography (EUVL) due to shape changes during suction chucking, which affect flatness control.
Innovation Solution
A 6-inch square synthetic quartz glass substrate with a central surface area of 132 mm square and a frame region, where the central surface area has a flatness of up to 50 nm and the frame region has a flatness of up to 150 nm, with a least squares average plane higher than the frame region by 50 nm to 100 nm, and a surface roughness of up to 0.10 nm, designed to maintain flatness when mounted on a stepper by suction chucking, and prepared through rough polishing, measurement, partial polishing, and finish polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gas cluster ion beam etching is used to achieve high flatness, then substrate flatness is improved, but processing time increases due to vacuum environment requirements
Solution Approach 1:
The substrate shape is designed in advance with predetermined curvature in the peripheral portion before mounting. This preliminary shaping compensates for the suction-induced deformation that will occur during stepper mounting, eliminating the need for time-consuming vacuum-based finishing processes.
Solution Approach 2:
The substrate is divided into a central portion (where high flatness is required for lithography) and a peripheral portion (where curvature is introduced). This segmentation allows different regions to have different shapes optimized for their specific functions, resolving the conflict between overall flatness and mounting stability.
2Manufacturing precision
If non-contact polishing is used to achieve high flatness, then substrate flatness is improved, but processing time increases due to low polishing rate
Solution Approach 1:
The substrate shape is predetermined during manufacturing with the peripheral portion designed to have specific curvature. This preliminary action achieves the flatness requirement through design rather than through slow non-contact polishing, dramatically improving productivity while maintaining the required precision.
3Stability of the object's composition
If substrate peripheral portion is made flat to control shape change during suction chucking, then mounting stability is improved, but flatness control within effective range becomes difficult
Solution Approach 1:
Different regions of the substrate are given different properties: the central portion maintains high flatness for lithography precision, while the peripheral portion is given controlled curvature for mounting stability. This local differentiation resolves the contradiction between overall stability and local flatness control.
Solution Approach 2:
Instead of making the entire substrate symmetrically flat, the invention introduces asymmetric curvature specifically in the peripheral portion while keeping the central portion flat. This asymmetric design allows the substrate to be more stable during suction chucking without compromising the flatness where it matters for lithography.
4Adaptability or versatility
If large size apparatus is used for substrate processing, then processing capability is improved, but capital investment and operation expenses increase
Solution Approach 1:
The substrate shape is predetermined during manufacturing with built-in compensation for suction-induced deformation. This allows the substrate to be processed and mounted using standard, smaller equipment without requiring expensive large-scale vacuum processing apparatus, reducing both capital investment and operating costs.
Data Source
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Figure 3~4
AI summary
A synthetic quartz glass substrate has a surface of 6 inch squares including a central surface area of 132 mm squares. The central surface area of 132 mm squares has a flatness of up to 50 nm. A frame region obtained by subtracting the central surface area of 132 mm squares from the central surface area of 148 mm squares has a flatness of up to 150 nm.