Simulations of step responses of electronegative radio-frequency capacitively coupled discharges

Abstract

The transient response of electronegative radio-frequency glow discharges is important for process control, charge free etching, and highly selective etch applications. The step response of typical electronegative process gases (silane at 1 Torr and chlorine at 100 mTorr) is studied using a drift-diffusion model for silane and a three-moment model for chlorine. The silane simulations include a blocking capacitor whereas the chlorine results do not. For the silane results with a blocking capacitor in series with the plasma, it is found that there are three types of transients. Depending on the final steady-state value of the source rf voltage, the step response can be characterized either by smooth transitions in the number densities of species in the discharge from one steady state to the next, temporary extinction of the discharge or a discharge mode characterized by temporary extinction and reignition of the discharge. In the case of silane definite thresholds separate the phenomena. The step response of the chlorine discharges is always characterized by a smooth transition from one steady state to the next. Smooth transitions from one steady state to the next in the case of step decreases in the source voltage are possible since decrease of the negative ion density in the bulk is controlled by ion–ion recombination. It appears that the temporary extinction of the discharge and natural pulsed steady state is the consequence of how the voltage is divided between the gap and the blocking capacitor during the transient and the fact that the attachment coefficient becomes larger than the ionization coefficient at low values of reduced electric field.

Current status and nature of high-frequency electronegative plasmas: basis for material processing in device manufacturing

“…93) Table IX gives the correlation between ( ) E N g Critical in DC static breakdown and the value [ ( ) ] E t N g eff in HF bulk plasma in the CCP estimated by the numerical modeling for several electronegative gases. 94,100,106,109,111,113,114,117) Figure 10 shows the good linear correlation between the reduced fields. Based on the results in Fig.…”

Two-dimensional modelling of CF4rf plasmas: periodic steady state, transient response after step change of power source voltage, and comparison with one-dimensional modelling

“…concentrations and fluxes of electrons, ions and radical species near a substrate surface. Such studies were presented by Lymberopoulos and Economou (1994) for Cl 2 plasmas and Yang et al (1997Yang et al ( , 1998 for Ar and SiH 4 plasmas.…”

Transient behaviour of CF4rf plasmas after step changes of power source voltage

“…In the present paper, in order to study the fundamental properties of transient CF 4 plasmas, we simulate the responses of CF 4 capacitively coupled plasmas to step changes of the amplitude of rf (radio-frequency, 13.56 MHz) power source voltage. We calculate the variations of the distributions of the charged particles and radicals (F, CF, CF 2 and CF 3 ) using a one-dimensional fluid model as previously performed for SiH 4 plasmas by Yang et al (1997Yang et al ( , 1998. Detailed analysis of the plasma behaviour and the evaluation of its relaxation speed would be informative to control the plasmas.…”