Analysis of ArF excimer laser system discharge characteristics in different buffer gases

Abstract

Excimer laser is the current mainstream source of international semiconductor lithography. The stable operation of the laser system directly affects the working efficiency of the semiconductor lithography machine, so it is very important to optimize the laser system. The buffer gas commonly used in ArF excimer laser systems is He, Ne. In the early years, Shinjin Nagai and Mieko Ohwa have studied the output characteristics of the system when using He or Ne as a buffer gas from the aspect of pump efficiency and gain coefficient, and pointed out that using Ne instead of He has no obvious advantages in terms of efficiency. However, when Ne is used as the buffer gas, the reaction between Ne and electrons is more complicated. In addition to direct ionization and excitation reactions, it also contains a large amount of step ionization and secondary ionization, which releases free electrons. The stability of the system is improved, when Ne is used as the buffer gas. The ArF excimer laser system discharge characteristics in different buffer gases are analyzed based on fluid model in the paper. The role of photoionization is discussed. The simulation results show that the width of the electron depletion layer and the cathode sheath are both smaller, and the discharge stability is higher when Ne is used as the buffer gas. The expansion of the discharge region is accelerated and the threshold voltage of the discharge is reduced by adding Xe into Ne to trigger photoionization. The excimer laser discharge process is very complicated and is affected by many factors. Only two factors of the buffer gas and the photoionization process are studied in this paper. The simulation model will be extended from one-dimensional case to two-dimensional case in the future, and multiple physical factors of the ArF excimer laser system will be considered.