| Power-modulated plasmas are a recent development that appears to be promising for improving thin film etching and deposition in electronic materials processing. However, there has been little information available for these systems.; In the present study, the performance of a power-modulated plasma was studied and compared to that of a traditional continuous-wave plasma through modeling and diagnostics. A comprehensive mathematical model of the oxygen glow discharge and etching of polymer in a parallel-plate reactor was developed to study the plasma kinetics (electron energy distribution function, electron transport and reaction rate coefficients, etc.), and to predict key internal plasma properties (self-sustained electric field, electron and radical densities, etc.), etch rate and uniformity. The model equations were solved by a finite-element method. The model included (a) the time-dependent Boltzmann transport equation, (b) a two-region glow discharge model composed of bulk plasma and sheath, and (c) a radical transport and reaction model.; Experiments were designed and performed for oxygen continuous-wave and power-modulated plasmas using a parallel-plate reactor to check the model validity. Key internal plasma properties were measured using optical emission spectroscopy and impedance analysis. Etch rate and uniformity of polymer etching were also measured.; Good agreement between theory and experiment was obtained over the range of power, pressure, flow rate and pulse period examined. It was found that power modulation (i) improved the etching uniformity as compared to the continuous-wave plasma, (ii) yielded higher etch rate (when prorated by the duty cycle) than the continuous-wave plasma for the same power dissipation, (iii) had a substantial effect on the relative concentration of radicals, and in turn on the etching selectivity and anisotropy, and (iv) can be used, along with optical emission spectroscopy, to determine the buildup and decay time of important radicals. |
