Characterization of pattern roughness for advanced technology nodes is crucial as it can adversely affect yield and carry detrimental consequences on device performance. While the main in-line working horse for roughness measurements has been the CDSEM, an In-line metrology reference to evaluate roughness measurement sensitivity is limited. Traditional reference tools such as TEM could provide so far limited roughness measurements statistics. A novel approach to evaluate sensitivity is to induce pre-designed pattern roughness on EUV mask and explore methods of signal enhancements on printed pattern wafers at different process steps. Three different types of pattern roughness are implemented: sinusoidal, chirped sinusoidal and random patterns, which have different predefined power spectrum aimed for characterizing measurement tools at different bandwidth. This paper described this technique and aims to characterize roughness with various metrology technologies such as: CDSEM, OCD, S-TEM, AFM and XCD on EUV printed resist wafer and post etch. The approach for enhancing sensitivity is through incorporation of window functions, which serve the purpose of removing extraneous information so that subsequent analysis, produce more meaningful results. Window functions perform pre-processing in the time domain to help improve results in subsequent processing in the frequency domain, which is beneficial for PSD calculation. Furthermore, coherent sampling is implemented which ensures that an integral number of cycles of the input signal is included within the time/scan frame, which is crucial for low frequency determination from acquired pattern roughness. The acquisition mode itself can contribute to induced non-related frequency or noise, more prevalent in the beginning and end of the time/scan series. This kind of distortions of proper frequency mapping named frequency leakage. In applications where the coherent sampling criteria cannot be met and proper frequency mapping disturbed by frequency leakage phenomena, a window weighting function can be applied to the time record to minimize spectral leakage
Shimon Levi, Kurt Ronse, Bogumila Kutrzeba-Kotowska , Gaoliang Dai, Frank Scholze, Igor Turovets, Laurens Kwakman, Kenslea Anne, Brid Connolly, Markus Bender, Sven Krannich, Vladislav Kaplan, Hamed Sadeghian, Nicole Nulkes-de Groot, and Maxim Rabinovitch, "Lines roughness holistic metrology sensitivity study supported by EUV mask designed with induced roughness (Conference Presentation)," Proc. SPIE 10585, Metrology, Inspection, and Process Control for Microlithography XXXII, 1058511 (Presented at SPIE Advanced Lithography: February 28, 2018; Published: 19 March 2018); https://doi.org/10.1117/12.2297265.5754464300001.
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