Mask Structure Characterization via Diffraction Intensity Quotients
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Solution Overview
Problem
Current methods for characterizing mask structures in semiconductor fabrication are either laborious when performed on wafers or prone to errors due to mask behavior during imaging, and are challenging to measure accurately due to resolution enhancement technologies.
Innovation Solution
A method involving illumination with monochromatic radiation at specific angles to produce diffraction patterns, capturing and analyzing these patterns to determine intensity quotients, which are less affected by exposure variations and allow for rapid, accurate characterization of mask structures with reduced computation time and increased tolerance for defocusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If CD measurement is performed on the mask using conventional methods, then measurement can be done early in the process, but errors caused by mask behavior during imaging and scanner intensification make the measurement inaccurate
Solution Approach 1:
The patent replaces conventional imaging-based measurement methods with diffraction-based optical measurement. Instead of using scanners or microscopes that are sensitive to mask behavior and imaging errors, the invention uses diffraction patterns to directly measure CD on the mask, eliminating the intermediate imaging steps that introduce errors.
Solution Approach 2:
The patent changes the measurement parameter from direct imaging to diffraction intensity analysis. By measuring the intensities of diffracted light at specific angles and calculating ratios of these intensities, the method obtains CD values that are independent of mask behavior during imaging and scanner intensification effects.
2Measurement precision
If CD measurement is performed on the wafer, then the final product is measured for accurate data, but the entire wafer exposure process must be performed making it very laborious
Solution Approach 1:
The patent performs CD measurement on the mask before the wafer exposure process, allowing early detection of CD deviations. This preliminary measurement avoids the need to complete the entire wafer exposure process just for measurement purposes, significantly reducing time and labor while still providing accurate CD data.
Solution Approach 2:
The patent measures the CD directly on the mask (the source) rather than requiring measurement on the wafer (the copy). By using diffraction patterns from the mask itself, the invention obtains measurement data without needing to produce actual wafer samples, eliminating the laborious exposure process.
3Manufacturing precision
If mask structures are optimized by resolution enhancement technology, then imaging quality is improved, but the mask structures no longer wholly match the structures to be imaged making CD measurement difficult
Solution Approach 1:
The patent replaces imaging-based measurement methods with diffraction-based measurement. Since diffraction patterns directly relate to the periodic structure of the mask lines and spaces, this method can accurately measure CD even when the mask structures have been optimized with RET features that would not appear in conventional images.
Solution Approach 2:
The patent changes from measuring spatial dimensions directly to measuring diffraction intensity ratios. The diffraction intensities at specific angles provide information about the CD that is independent of the specific structural optimizations applied through RET, allowing accurate measurement despite structural modifications.
4Loss of information
If aerial images of masks are analyzed with mask inspection microscope, then most features projected onto the wafer are shown, but computation time for image analysis is lengthy
Solution Approach 1:
The patent replaces complex image analysis with simple diffraction intensity ratio calculation. Instead of capturing and processing aerial images that require lengthy computation to extract CD information, the invention uses diffraction patterns where CD can be determined directly from intensity ratios at specific angles, dramatically reducing computation time.
Solution Approach 2:
The patent extracts only the essential information needed for CD measurement from the diffraction pattern - specifically the intensities at certain angular positions. This selective extraction of critical parameters avoids the need to process and analyze entire aerial images, reducing computation time while maintaining measurement accuracy.
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 enables fast, accurate, and cost-effective characterization of mask structures with improved reproducibility and reduced dependence on position variations, allowing for efficient measurement of critical dimensions.
Implementation Method 1
illuminating the mask with monochromatic illuminating radiation under at least one angle of illumination, so as to obtain a diffraction pattern of the structure
Data Source
AI summary
A method is provided for characterizing a mask having a structure, comprising the steps of: illuminating said mask under at least one illumination angle with monochromatic illuminating radiation, so as to produce a diffraction pattern of said structure that includes at least two maxima of adjacent diffraction orders, capturing said diffraction pattern, determining the intensities of the maxima of the adjacent diffraction orders, and determining an intensity quotient of the intensities. A mask inspection microscope for characterizing a mask in conjunction with the performance of the inventive method is also provided.