Simulation and Compensation Methods for EUV Lithography Masks with Buried Defects

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. This dissertation describes the development and application of a new simulator, RADICAL, which can accurately simulate the electromagnetic interaction in extreme ultraviolet (EUV) lithography at a wavelength of 13.5nm between the mask absorber features and a buried multilayer defect three orders of magnitude faster than rigorous methods. RADICAL achieves this performance by using simulation and modeling methods designed specifically for the individual EUV mask components simulated. The nonplanar nature of a multilayer coated buried defect can be simulated using a ray tracing method developed by Michael Lam, or the faster advanced single surface approximation (SSA) for shorter defects with more uniform layers below the mask surface, and the absorber is modeled using a propagated thin mask model which efficiently accounts for the thickness of the absorber material. The multilayer and absorber simulation results are linked by a Fourier transform which converts the electric field output by one simulator into a set of plane waves for the next. As a new form of projection lithography technology, EUV is fundamentally different than current technologies and therefore requires new methods for mask analysis, inspection and compensation. At the 13.5nm wavelength, all materials have a refractive index of around unity and are absorptive. This means that EUV masks must be reflective multilayers. Understanding the electromagnetic response of these new masks, specifically the effects of multilayer defects requires new simulation methods, such as RADICAL. The accuracy and speed of RADICAL has been verified by comparisons with rigorous finite difference time domain (FDTD) simulations, rigorous waveguide method simulations, and actinic inspection experiments provided by Lawrence Berkeley National Laboratory (LBNL) and Intel. RADICAL matches the critical dimension (CD) predicted by FDTD within 1nm for defects up to 2.5nm tall on the multilayer surface. It matches actinic inspection results, within the error of the experiment, for defects up to 6.5nm tall on the surface. This accuracy is acceptable because the EUV defects expected in production lithography are expected be 2nm tall or less. RADICAL is typically about 1,000 times faster …