Mask Inspection Microscope Aerial Image Characterization
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Solution Overview
Problem
Current methods for characterizing critical dimensions of structures on masks, such as in semiconductor production, face challenges including increased errors due to mask behavior during imaging and the complexity of measuring on wafers, where structures optimized by resolution enhancement technology do not correspond to those imaged, making precise measurement difficult.
Innovation Solution
A microscope with an illumination unit for non-axial illumination and an imaging unit that images aerial images within a defocus region, utilizing an imaging field stop to encompass or cut the aerial image, allowing for accurate measurement without refocusing and reducing stray light, along with a method for recording diffraction images that includes determining intensity ratios of adjacent orders for precise characterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wafer measurement is performed to characterize structures, then the end product is measured which is significant, but the complete process of wafer exposure needs to be carried out which makes it very complicated
Solution Approach 1:
The patent uses a mask inspection microscope to create an aerial image copy of the mask structure, which simulates the imaging properties of a scanner. This copying approach allows measurement of the aerial image directly on the mask without performing the complete wafer exposure process, thereby maintaining measurement significance while reducing process complexity
2Measurement precision
If structure characterization is performed on the mask itself, then errors as a result of mask behavior during imaging are not incorporated, but mask structures optimized by resolution enhancement technology do not completely correspond to the structures to be imaged which renders measurement difficult
Solution Approach 1:
The patent introduces defocus as a controlled parameter change to simulate the imaging conditions of a scanner. By intentionally defocusing the aerial image and using a field stop to encompass or circumferentially cut the image, the measurement incorporates the effects of mask behavior during imaging while working with the actual mask structure rather than trying to achieve perfect correspondence with the final imaged structure
3Measurement precision
If aerial image evaluation is performed using a mask inspection microscope, then the aerial image largely exhibits the features that are also imaged on the wafer, but lateral displacement of the aerial image depending on position within the defocus region occurs which complicates measurement
Solution Approach 1:
The patent addresses lateral displacement by introducing a field stop that operates in the lateral dimension. By dimensioning the field stop opening to encompass or circumferentially cut the aerial image despite its lateral displacement, the measurement system maintains accuracy across different positions within the defocus region without requiring refocusing for each measurement point
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, cost-effective, and accurate characterization of mask structures with reduced errors, allowing for measurement at different points without refocusing and providing consistent intensity evaluation, enhancing the precision and speed of characterizing critical dimensions.
Implementation Method 1
A microscope and method for recording diffraction images are described
Data Source
AI summary
A microscope includes an illumination unit for illuminating a mask at a predetermined non-axial illumination angle, an imaging unit for imaging an aerial image of the mask within a predetermined defocus region, and an imaging field stop, in which as a result of the lateral displacement of the aerial image depending on the position within the defocus region and on the non-axial illumination angle, the opening of the imaging field stop is dimensioned such that the aerial image is either completely encompassed or circumferentially cut within the defocus region.A method for characterizing a mask having a structure includes illuminating the mask at at least one illumination angle using monochromatic illumination radiation such that a diffraction image of the structure is created, recording the diffraction image, establishing the intensities of the maxima of the adjacent orders of diffraction, and establishing an intensity ratio of the intensities.