Mask Inspection Microscope Calibration for EUV Lithography
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Solution Overview
Problem
The dimensions of patterns determined from aerial images produced by a mask inspection microscope differ significantly from those generated by a scanner, leading to inaccurate predictions of the resulting structure on a wafer, due to differences in illumination area sizes and scattering center effects.
Innovation Solution
A method is developed to determine a correlation between the characteristics of aerial images from a mask inspection microscope and those from a scanner, allowing for accurate calculation of wafer pattern dimensions by recording aerial images, determining characteristic values, and applying a correlation factor to improve calibration accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mask inspection microscope is used to determine pattern dimensions, then the mask can be inspected for defects, but the dimensions differ significantly from those produced by a scanner, leading to inaccurate predictions of wafer structure
Solution Approach 1:
The patent changes the parameters of the mask inspection microscope to match scanner conditions by adjusting the illumination area size and introducing scattering centers. This allows the microscope to reproduce scanner-like aerial images, enabling accurate prediction of wafer structure dimensions while maintaining the ability to inspect mask defects.
Solution Approach 2:
The patent creates a copy of the scanner's imaging conditions by configuring the mask inspection microscope to produce equivalent aerial images. By matching illumination settings, numerical aperture, and introducing scattering centers, the microscope replicates scanner behavior, allowing defect inspection with accurate dimension prediction.
2Ease of operation
If the illumination area of the mask inspection microscope is made smaller compared to scanners, then the microscope can focus on specific mask regions for defect inspection, but this causes deviations in aerial image characteristics from scanner-produced images
Solution Approach 1:
The patent adjusts the illumination area parameter of the mask inspection microscope to match the scanner's illumination area size. This parameter change ensures that the aerial images produced by the microscope have the same characteristics as scanner-produced images, enabling accurate dimension prediction while maintaining the microscope's ability to inspect specific mask regions.
3Manufacturing precision
If scattering centers are introduced into the mask to optimize critical dimension, then the mask transmission and reflectivity are modified for better pattern fidelity, but the scattering center effects create differences between microscope and scanner aerial images
Solution Approach 1:
The patent converts the harmful effect of scattering centers, which create differences between microscope and scanner images, into a beneficial effect. By intentionally introducing scattering centers into the mask and matching them between the microscope and scanner, the patent uses these scattering effects to improve critical dimension optimization while maintaining agreement between microscope and scanner aerial image dimensions.
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 method enables precise determination of wafer pattern dimensions from mask inspection microscope images, significantly improving the accuracy of predicting the structure on the wafer by accounting for illumination area differences and scattering center effects.
Implementation Method 1
local density variations are introduced into the mask that function as scattering centers. The transmission and reflectivity of the mask are modified by the local density variations.
Implementation Method 2
the scattering centers are introduced into the mask by pulsed femtosecond lasers
Implementation Method 3
The introduction of scattering centers into extreme ultra-violet (EUV) masks by using electron beams is known from German patent application DE 10 2011 080 100 A1. In this method, scattering centers are introduced into the reflecting multilayer of the mask in order to reduce reflectivity.
Data Source
AI summary
A method is provided for emulating the imaging of a scanner mask pattern to expose wafers via a mask inspection microscope, in which the mask was corrected by introducing scattering centers. The method includes determining a correlation between the first values of at least one characteristic of aerial images of the mask pattern as produced by a mask inspection microscope and the second values of the at least one characteristic of aerial images of the mask pattern as produced by a scanner, recording a first aerial image of the mask pattern with the mask inspection microscope, determining the first values of the at least one characteristic from the first aerial image, and determining the second values of the at least one characteristic of the first aerial image, using the correlation. A mask inspection microscope is also provided for emulating the imaging of a mask pattern of a scanner to expose wafers, in which the mask was corrected by introducing scattering centers.