Comparison of EUV Photomask Metrology Between CD-AFM and TEM  

作　　者：Gaoliang Dai Kai Hahm Lipfert Sebastian Markus Heidelmann 

机构地区：[1]Physikalisch-Technische Bundesanstalt,38116,Braunschweig,Germany [2]Advanced Mask Technology Center GmbH&Co.KG,01109,Dresden,Germany [3]ICAN,Universität Duisburg-Essen,47057,Duisburg,Germany

出　　处：《Nanomanufacturing and Metrology》2022年第2期91-100,共10页纳米制造与计量（英文）

基　　金：Open Access funding enabled and organized by Projekt DEAL.

摘　　要：Accurate metrology of extreme ultraviolet (EUV) photomask is a crucial task. In this paper, two different methods for reference EUV photomask metrology are compared. One is the critical dimension atomic force microscopy (CD-AFM). In the measurements, the contribution of its AFM tip geometry is usually the dominant error source, as measured AFM images are the dilated results of measured structures by the AFM tip geometry. To solve this problem, a bottom-up approach has been applied in calibrating the (effective) AFM tip geometry where the result is traceably calibrated to the lattice constant of silicon crystals. The other is transmission electron microscopy (TEM). For achieving measurement traceability, structure features are measured in pairs in TEM images;thus the distance between the structure pair calibrated by a metrological AFM in prior can be applied to determine the magnification of the TEM image. In this study, selected photomask structures are calibrated by the CD-AFM, and then sample prepared and measured by high-resolution TEM nearly at the same location. The results are then compared. Of six feature groups compared, the results agree well within the measurement uncertainty, indicating excellent performance of the developed methodology. This research supports the development of a photomask standard, which is applied as a “reference ruler” with improved low measurement uncertainty in photomask fabs.

关 键 词：Extreme ultraviolet(EUV)photomask standard Traceable calibration METROLOGY Critical dimension(CD) Atomic force microscopy(AFM) Transmission electron microscopy(TEM) High precision Low measurement uncertainty 

分 类 号：TB383[一般工业技术—材料科学与工程]