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EUV pellicles guarding masks from defects and dynamic gas lock thin film windows are considered a corner stone for using EUVL in chip production. For providing such thin film products with certified features EUV actinic metrology tools are needed in the industrial supply chain. For best conservation of optical quality and throughput in the scanner, such EUV pellicles should have high transmission of > 90 % with a transmission uniformity of > 99.6 %, low reflectance of much less than 0.1 % and low scatter of EUV.
The specification for the ideal metrology tool is qualifying a full sized EUV pellicle with precision of better 0.1 % for transmission and 0.001% for reflection, the ability to quantify the scatter distribution. The measurements should be accomplished in acceptable process time and should neither add contaminate nor particulate to the product under test.
Within RI Research Instrument’s support of EUVL infrastructure by developing actinic metrology solutions, we have engaged in this task by applying our proprietary effective inband EUV metrology scheme described elsewhere.
While the first generation tool has been presented elsewhere, we now present general considerations on measurement process and tool architecture for the combined three tasks in the second generation tool. Full pellicle transmission and reflectance mapping are measured in less than 2 hours fully automatic process time (careful load-locking included). Measured transmission show precision and accuracy of better 0.1 % for a qualification pixel resolution of 300x300 µm2. Performance of the reflectance measurements is under investigation but expected to be in the range of 0.001 % precision demonstrated in proof of concept experiments in our application lab. The first generation tool is used by our customer in routine pellicle production and is constantly running with uptimes better than 95%.
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