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%.
RI Research Instrument’s EUV pellicle transmission qualification tool EUV-PTT uses "effective inband EUV measurement" which is spectrally filtering emission of the EUV-Lamp to 2% bandwidth at 13.5 nm for measuring "as seen by the scanner". Images of about 20x20 mm2 are recorded in less than 5 seconds. A full pellicle characterization with < 60 images taken is accomplished in less than one hour. The first prototype of the EUV-PTT is in production quality control since nearly one year at our customer and achieving targeted quality in measurement and cleanliness and meets uptime specifications. Amongst additional aspects to be addressed in quality control is the reflection from the pellicle, which - in worst case - may impair the printing performance in the scanner. Hence, recently, we have performed concept studies on applying the PTT technique to carbon nano tube pellicles and on measuring the reflectance of low reflectance samples are reported. The latter is heavily demanding as reflectances in the range of 0.02 % were measured with sensitivities and reproducibilities in the range of 0.002 %.
RI Research Instrument’s EUV pellicle transmission qualification tool EUV-PTT uses “effective inband EUV measurement” which is spectrally filtering emission of the EUV-Lamp to 2% bandwidth at 13.5 nm for measuring “as seen by the scanner”. Images of about 20*20 mm² are recorded in < 5 seconds. A full pellicle characterization with < 60 images taken is accomplished in less than one hour.
Recently, we have performed some studies on applying this technique to carbon nano tube pellicles and on measuring the reflectance of pellicles which will be reported. The latter is heavily demanding as reflectances in the range of 0.01 % were measured with sensitivities and reproducibilities in the range of 0.002 %.
The scene is set for EUV lithography high volume production. EUV masks with pellicles and scanners with dynamic gas lock thin film windows are considered a corner stone for insertion. For making the thin films usable in EUV scanners, EUV actinic metrology with high precision and accuracy is required to qualify them. One of the key features is the uniformity of the transmission at 13.5 nm through the thin film membrane to be qualified over the entire area. The specification for the required tool is qualifying a full sized EUV pellicle with an average EUV transmission of around 90 % to a uniformity of < 99.6 % – hence precision and accuracy of the process of below 0.1 % are demanded. Certainly, no particles should be added to the EUV pellicle by the qualification measurement. Within RI Research Instrument’s support of EUVL infrastructure by developing actinic metrology solutions, we have built a dedicated tool for EUV pellicle transmission characterization using the effective inband EUV scheme. The actinic measurement of the full pellicle is accomplished in less than 40 minutes. Vacuum loading and unloading consumes another 35 minutes due to the need of extreme care for such fragile samples and to avoid contamination. First images of full sized pellicles show precision and accuracy of better 0.1 % for a qualification pixel resolution of 300x300 μm2.
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