Evaluation of ion concentrations in plasma for technological processes in microelectronics

In this work results of a theoretical study which embraced numerical evaluations of the plasma composition as a function of pressure and temperature are given for high-pressure (from 0.1 MPa to 2.5 MPa) and low-temperature (from 2000 K to 20000 K) krypton plasmas containing up to 25% of added sodium. It is assumed that the system is kept under constant pressure and that a corresponding state of local thermodynamical equilibrium is attained in it. A previously derived modified expression for the Debye radius, offering the possibility to treat the plasmas considered as weakly non-ideal in the whole temperature range of interest, is used in the evaluations, in combination with the Saha equations for the relevant ionization stages of both Kr and Na. It is found that the addition of as little as 1% of sodium profoundly alters the properties of the plasma. Thus, ion (and electron as well) number densities monotonically increasing with temperature (with pressure kept constant) much as in the pure krypton plasma, become considerably higher. The overall enhancement is by about one order of magnitude below 10000 K.