Fast simulation methods and modeling for extreme ultraviolet masks with buried defects

To support the successful implementation of extreme ultraviolet (EUV) lithography for high volume manufacturing, a spectrum of simulation tools is needed. For investigation of new materials and geometries, rigorous but computationally expensive simulations are required. For faster simulations, a new method, rapid absorber defect interaction computation for advanced lithography (RADICAL), is introduced. RADICAL is a modular program, that uses separate methods to simulate the absorber pattern and defective multilayer. Two different methods are used to simulate the multilayer within RADICAL: ray tracing and single surface approximation (SSA). Ray tracing can accurately simulate arbitrary multilayer geometries. SSA is only accurate for defects shorter than 4.5 nm on the multilayer surface. With ray tracing, RADICAL is nearly 1000 times faster than finite difference time domain (FDTD) for simulating line-space patterns over buried defects. RADICAL with SSA is nearly 25,000 times faster than FDTD. The accuracy of RADICAL is shown to be excellent for simulating defects in focus, and for simulating defects smaller than 2.5 nm through focus. The error can be as high as 4 nm in predicting CD change for larger defects out of focus due to the complexities of modeling the phase of buried defects. But this error is predictable and will likely be acceptable for most applications considering the huge speed advantages of RADICAL.