EUV Lithography Focus Monitoring via Optical Roughness Analysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Maintaining focus during extreme ultraviolet (EUV) lithography processes is challenging due to factors like wafer movement and changes in the radiation path, leading to degradation of patterns and increased critical dimensions, which affects the yield of semiconductor manufacturing.
Innovation Solution
The EUV lithography system employs a method to measure and monitor focus quality using parameters like line-width roughness (LWR) and standard deviation of circular perimeter, providing a more accurate defocus window and enabling preventive actions to maintain optimal focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional air gauge or similar mechanisms are used for focus monitoring, then the system structure remains simple, but focus monitoring accuracy deteriorates and becomes unreliable in EUV vacuum environment
Solution Approach 1:
The patent replaces mechanical focus monitoring mechanisms (air gauges) with an optical-based measurement system that uses EUV light reflection and interferometry to detect focus deviations, enabling accurate focus monitoring in the vacuum environment required for EUV lithography
Solution Approach 2:
The patent introduces an intermediary measurement system that uses test patterns and optical reflection as a mediator between the EUV exposure system and the control system, allowing indirect but accurate focus measurement without requiring direct mechanical contact in the vacuum environment
2Productivity
If feature sizes are reduced to increase functional density, then production efficiency improves, but focus control difficulty increases and pattern fidelity deteriorates
Solution Approach 1:
The patent implements a feedback control system that continuously monitors focus deviations using test patterns and automatically adjusts the focus position to compensate for drift, ensuring consistent pattern fidelity even as feature sizes are reduced for higher productivity
Solution Approach 2:
The patent performs preliminary focus calibration and measurement using test patterns before production exposure, and implements continuous focus monitoring during exposure to prevent focus drift from degrading pattern quality at reduced feature sizes
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 improves the yield of semiconductor manufacturing by precisely monitoring focus variations, reducing the risk of catastrophic failures and maintaining pattern fidelity, even as feature sizes decrease.
Implementation Method 1
an EUV source; a wafer holder configured to hold a wafer to be exposed to EUV radiation from the EUV source
Implementation Method 2
EUV scanners use reflective rather than refractive optics, i.e., mirrors instead of lenses
Data Source
AI summary
A method of evaluating a focus control of an extreme ultraviolet (EUV) lithography apparatus includes preparing a wafer exposed by using the EUV lithography apparatus. The wafer includes test patterns formed of a photoresist and having circular islands or holes prepared by multiple exposures of EUV at different foci of exposure. The method further includes measuring a roughness parameter of the test patterns and estimating a function representing a dependence of the roughness parameter on the focus. A best focus is estimated based on an extremum of the function. Exposure wafers are then exposed to EUV with the best focus. The exposure wafers include the test patterns. The roughness parameter for the test patterns on the exposure wafers obtained by exposing the exposure wafers at the best focus is periodically measured. An abnormality in focus is then determined based on the measured roughness parameter and the function.