The Simple Model for Ion-assisted Etching Using Cl2/Ar Inductively Coupled Plasma

Abstract

In the case of chemical active gas to be used for the etching of the material forming low-volatile reaction products, the etching result is affected by the chemical and physical factors together. Chemical factor is controlled by the fluxes of chemical active species (atoms, radicals) on the etched surface. Physical factor is represented by the sputter etching as well as by the ion-assisted etching through the ion-stimulated desorption of the reaction products. In our model, we combined the description of volume and surface kinetics aimed to establish the interconnections between input process parameters and etch rate. The description of volume kinetics and the mass content of neutral and charged particles is based on 0-dimensional plasma modeling in the quasi-stationary approximation. For these purposes, we used two methods. In first method, we assumed Maxwellian electron energy distribution function (EEDF) and used the electron density and electron temperature determined by Langmuir probe measurements as input parameters for modeling. In second method, we used the self-consistent solution of Boltzmann kinetic equation, power balance equation and balance kinetic equations of the formation and decay for Cl2, Cl, Cl2+, Cl+, Cl-. Both methods give the similar results confirming that for the ICP system operating in low-pressure region the real EEDF is close to Maxwellian. To analyze the surface kinetics including both sputtering and chemical reaction, the theory of active surface sites was applied. The model shows a good agreement with the published data concerning the plasma parameters as well as etches rate behaviors. The model also explains the non-monotonous effects on the etch rate dependence on Cl2/Ar mixing ratio both for the cases of low-volatile and high-volatile reaction products.