Use of Raman spectroscopy in characterizing soft x-ray multilayers: tools in understanding structure and interfaces

Abstract

Our group is studying the structure and interfaces of soft x-ray multilayers by various techniques including x-ray diffraction and Raman spectroscopy. Raman spectroscopy is particularly useful since it is sensitive to the identity of individual bonds and thus can potentially characterize the abruptness of interfaces in multilayers.Blocking interfacial mixing is very important in achieving and maintaining high reflectivity. We report our studies of the as-deposited and postannealed structure of Mo/Si and W/C multilayers. The Mo/Si system is probably th most widely studied multilayer currently because of its potential applications for soft x-ray projection lithography for the range of 13 to 15 nm. A high normal-incidence, peak reflectance is mandatory for imaging applications that involve many reflections. The reported theoretical and achieved reflectances of the Mo/Si system are 80% nd 65 % respectively. This loss of 15 % can bring about a six-fold loss in system throughput in the eight-reflection system contemplated. The interfaces in the Mo/Si system are thought to play a significant role in the degradng reflectance so characterization techniques which have interfacial sensitivity are particularly important. The Io'Si multilayer system is susceptible to Raman characterization since both the a-Si spacer layer and the MoSi, compwnd which fonus at the interface have Raman active modes. In this paper we report the first Raman studie, to be of our knowledge, of the a-Si layers and their crystallization and the crystallization of the Mo/Si interface of the multilayer brought about by a one-hour 1000 °C anneal. These changes are apparent in the Raman spectra bef3fe they can be unambiguously detected by x-ray diffraction. 0-8194-1