A simple null-field ellipsometric imaging system (NEIS) for in-situ monitoring of EUV-induced deposition on EUV optics

We describe a null-field ellipsometric imaging system (NEIS) that provides for the real-time imaging of carbon deposition profiles on extreme-ultraviolet (EUV) optics in a vacuum system. NEIS has been demonstrated at NIST on a small chamber that is used for EUV optics lifetime testing. The system provides images of carbon deposition spots with sub-nanometer resolution thickness measurements that maintain good agreement with those from ex-situ spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). The system will be implemented on several synchrotron beamlines for real-time monitoring of carbon film growth on optics during EUV irradiation.