Microlithographic Mask Characterization Apparatus with Intensity Normalization
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Solution Overview
Problem
Current methods for characterizing microlithographic masks in microlithography processes face challenges in accurately distinguishing between mask defects and light source energy fluctuations, leading to potential misinterpretation of defects during the characterization process.
Innovation Solution
An apparatus and method that output couple a portion of coherent light from the light source to an intensity sensor, allowing for normalization of images recorded by the sensor unit, thereby differentiating between brightness variations caused by the mask or the light source, and utilizing a scanning microscope configuration that emulates the projection exposure apparatus, with adjustable optical elements for precise illumination and energy measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a scanning microscope configuration is used to emulate projection exposure apparatus conditions, then measurement accuracy under lithography conditions is improved, but the ability to distinguish mask defects from light source fluctuations deteriorates
Solution Approach 1:
The optical path is segmented into two separate measurement channels: one for capturing mask images and another for monitoring light source intensity. This segmentation allows independent measurement of mask defects and light source fluctuations, resolving the contradiction by enabling both accurate lithography-condition measurement and defect distinction capability
Solution Approach 2:
An intermediary intensity sensor is introduced to monitor light source output separately. This intermediary measurement serves as a reference that mediates between the light source and the mask imaging process, allowing the system to distinguish whether intensity variations originate from the light source or mask defects
2Measurement precision
If the same illumination settings are used in the mask inspection apparatus as in the projection exposure apparatus, then emulation accuracy is improved, but the complexity of the inspection apparatus increases
Solution Approach 1:
The illumination settings and optical configuration of the projection exposure apparatus are copied into the mask inspection apparatus. This copying approach achieves accurate emulation of lithography conditions without requiring complete duplication of the entire exposure system, thereby maintaining reasonable complexity while improving measurement accuracy
3Measurement precision
If a diffraction-limited light spot is used for scanning the mask, then spatial resolution is improved, but the scanning time increases
Solution Approach 1:
The scanning process uses periodic illumination with the diffraction-limited light spot, systematically moving the spot across the mask in a controlled sequence. This periodic scanning approach maintains high spatial resolution while optimizing the scanning speed through efficient path planning and timing
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 fast and reliable characterization of microlithographic masks by accurately differentiating between mask defects and light source fluctuations, ensuring precise identification of relevant defects with high accuracy, even with minor energy variations, and allowing for efficient use of light resources.
Implementation Method 1
at least one light source which emits coherent light
Implementation Method 2
an illumination optical unit which produces a diffraction-limited light spot on the mask from the coherent light
Data Source
AI summary
The invention relates to an apparatus and a method for characterizing a microlithographic mask. According to one aspect, an apparatus according to the invention comprises at least one light source which emits coherent light, an illumination optical unit which produces a diffraction-limited light spot on the mask from the coherent light of the at least one light source, a scanning device, by use of which it is possible to implement a scanning movement of the diffraction-limited light spot relative to the mask, a sensor unit, and an evaluation unit for evaluating the light that is incident on the sensor unit and has come from the mask, an output coupling element for coupling out a portion of the coherent light emitted by the at least one light source, and an intensity sensor for capturing the intensity of this output coupled portion.