Microlithography Mask Characterization via Reflection Mode
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Solution Overview
Problem
Characterizing microlithographic wafers or masks in three dimensions is challenging due to unwanted defects and the limitations of existing methods, particularly in transmission mode for x-ray wavelengths, where absorption effects hinder three-dimensional microscopic characterization.
Innovation Solution
A method involving illumination with a high numerical aperture and a multiple layer model for simulating diffraction images, allowing for three-dimensional characterization in reflection mode, where the illumination and detection occur on the same side of the object, facilitating a high-resolution reconstruction of the refractive index profile and interface reflectivities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmission mode characterization is used for x-ray wavelengths, then three-dimensional microscopic characterization can be achieved, but absorption effects of substrate materials prevent successful characterization
Solution Approach 1:
The patent inverts the conventional transmission mode by using reflection mode characterization. Instead of illuminating the sample from one side and detecting from the opposite side, the illumination device and detector device are positioned on the same side of the object plane, detecting reflected diffraction images to achieve three-dimensional characterization without suffering from substrate absorption effects
Solution Approach 2:
The patent changes the operational parameters by working in the reflection regime rather than transmission regime for x-ray wavelengths. This parameter change allows the electromagnetic radiation to interact with the sample in a manner that avoids absorption by substrate materials while still enabling three-dimensional refractive index profile reconstruction
2Measurement precision
If high numerical aperture illumination is used to achieve large angle of incidence ranges, then three-dimensional resolution is improved, but rotation of the object becomes necessary which may not be desirable
Solution Approach 1:
The patent achieves large angle of incidence ranges by utilizing the angular space in the reflection geometry rather than rotating the object. By positioning the illumination and detection systems on the same side and using appropriate optical paths, the system accesses a wide range of incidence angles through the reflection process itself, eliminating the need for object rotation while maintaining three-dimensional resolution
3Reliability
If comprehensive mask characterization is performed before mass production, then imaging capability can be verified, but the complexity and time required for characterization increases
Solution Approach 1:
The patent enables comprehensive three-dimensional mask characterization to be performed efficiently by using a continuous measurement process in reflection mode. The method captures complete diffraction information from multiple angles and wavelengths in a systematic manner, allowing full characterization without requiring multiple separate measurement steps or object manipulation, thus reducing characterization time while maintaining reliability
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
Enables three-dimensional microscopic characterization with high resolution and accuracy, overcoming the limitations of existing methods by providing a suitable algorithm for evaluating measurement results and reconstructing object parameters, thus ensuring reliable imaging capability before mass production.
Implementation Method 1
a detector device for capturing a respective intensity distribution in a diffraction image produced by the object
Implementation Method 2
the illumination device and the detector device are arranged on the same side of the object such that the diffraction image is captured in reflection
Data Source
AI summary
A method includes using an illumination device to illuminate an object with electromagnetic radiation produced by a radiation source, and using a detector device to capture a respective intensity distribution in a diffraction image produced by the object in a plurality of measurement steps. The measurement steps differ from one another with respect to the illumination setting set by the illumination device. The method also includes determining at least one characteristic variable that is characteristic for the object on the basis of an iteratively performed comparison between the measurement values obtained within the scope of the measurement steps and model-based simulated values. The model-based simulated values are ascertained on the basis of a multiple layer model, in which the object is modeled by a multiple layer structure made of layers that are respectively separated from one another by an interface, wherein a location-dependent reflectivity is assigned to the interfaces.