In capacitively coupled radio frequency (rf) discharges, as used in plasma processing of semiconductor materials, controlling the electron energy distribution function f(ε) is important for controlling the flux of radicals and ions to the substrate. The strategies for controlling f(ε) include varying the gas mixture, frequency, pressure and pulse power format. Customizing the f(ε) is related to balancing the electron heating and cooling mechanisms. Multi-frequency capacitively coupled plasmas (CCPs) provide an opportunity to customize f(ε) through using pulsed plasmas. For example, a low frequency (LF) is typically applied to the lower electrode to control ion energy distributions and a high frequency (HF) is applied to the upper electrode to heat electrons. By pulsing the HF one can modulate f(ε) to produce shapes that are not otherwise attainable using continuous wave excitation. For example, an f(ε) may be produced that has both a high energy tail and a large thermal component. These f(ε) will produce different dissociation patterns in the feedstock gases. The choice of pressure, duty cycle and pulse repetition frequency (PRF) are important to the time average f(ε) as these determine the relative role of thermalization. Pressure also has a role in determining the dominant electron heating mechanism between ohmic heating and stochastic heating.

The customization of f(ε) in 2-frequency CCPs will be discussed using results from a 2-dimensional plasma equipment model. The electron f(ε) are obtained using a Monte Carlo simulation including electron-electron collisions. The consequences of PRF, duty cycle and HF power on f(ε) will be discussed for pressures of tens of mTorr in argon and fluorocarbon gas mixtures. The correlation between these parameters and f(ε) on the identity of radical and ion fluxes onto the substrate will be made.

* Work supported by the Department of Energy Office of Fusion Energy Sciences and the Semiconductor Research Corp.