A superfast 3D lithography simulator and its application for ULSI printability analysis

Printability challenges are already one of the key limits of new technology generations and the situation will become even worse with the delay in the introduction of 157nm lithography. To optimize the set-up of RET and verify their efficiency within a photo process window, it has become necessary to run detailed lithography simulations. While some 1-D test patterns can be simulated using the 2-D software tools, patterns such as line-ends, corners and metal islands should be evaluated by 3-dimensional simulators. Such a simulator can be calibrated using a small number of in-line measurements and then employed to analyze the “difficult to print patterns”. However, until recently the computational efficiency of such a 3-D tools has not been sufficient for practical applications. Since a lot of features under study are axial-symmetric, symmetry of the 3-D structures can be used to reduce computational complexity. To address this issue, we have developed a method to simulate three-dimensional axial-symmetrical structures. This method is based on the observation that scattering in and out of axial symmetrical structure can be classified into four kinds of scattering waves and each kind of scattering wave can be computed separately. Based on this observation, we have greatly reduced the run time and memory usage of the rigorous waveguide method without any loss of accuracy. According to our experiments, memory usage was reduced to one-forth and run time was shortened to 3~5% of the original simulation. (20-30 times speed up) In this paper, we will discuss applications of the new symmetrical simulator METROPOLE-3D to lithography simulation and layout analysis. We will discuss the fast calibration of METROPOLE-3D simulator. The simulated CD data was compared with experimental FEM wafer data to calibrate the parameters used in PEB and photoresist development. We are now able to analyze a lot of axial symmetrical dense and isolated 2-D structures with unprecedented speed. In this paper, wee will present a full lithography analysis example from a real product manufactured in the state-of-the-art lithography process.