Lithography modelling
The simulation is a transverse activity of the LTM, especially in the lithography group. Internal computation tools are developed when there is no adapted simulation means, like in the EUV lithography domain. Our works are then oriented on the computation codes for electromagnetic simulation. The evolution of the hardware tools allows developing 3D codes based on a modal method (MMFE, Modal Method by Fourier Expansion also well known as RCWA (Rigorous Coupled Wave Analysis). An original approach is also studied with the wavelet expansion. This technique, widely used in signal processing, is used here to solve the wave equation using modal methods. The main idea is to benefit of the specific properties of the wavelets to reduce the number of elements used in the basis for the modal expansion. This multi-resolution approach allows improving significantly the convergence, and is therefore very efficient to reduce computing time.
Optical Proximity Corrections (OPC) techniques are now becoming compulsory for the improvement of the pattern printing of the more advanced generations of CMOS integrated circuits. The idea of these corrections is to modify and adapt the geometry of the mask pattern to compensate for process distortions. . The results on the final mask pattern can lead to very complex structures. It means that regarding these structures, we must be capable to know the consequences of the lithographic process variation on pattern printing. These variations can appear due to many reasons (source, mask, aberrations, etc…). Those which impact the most the process are the dose and the focus variations. That is why the goal of the works realized in LTM is to develop a technique allowing quickly qualifying the printing regarding the process window. This method allows monitoring patterns placement and significantly improving the overall process latitude.
