Investigation of SiO2 etch properties using pulse power in capacitively coupled plasmas

Summary form only given. The fluxes of radicals and ions to the wafer in plasma processing of microelectronic devices determine the quality of the etch or deposition. These fluxes are ultimately controlled by controlling and customizing the electron energy distribution function f(ε) which determines the dissociation patterns of feedstock gases. In quasi-steady state operation, an equilibrium condition for f(ε) results from a real time balance between electron sources and sinks. As such, for a given geometry, pressure and frequency of operation, there is not much latitude in controlling f(ε). By using pulse power, electron sources and sinks do not need to instantaneously balance - they need to balance only over the longer pulse period. This provides additional leverage to control f(ε). For example, during the power-on portion of the pulse cycle, high energy electrons are generated due to an overshoot of E/N above the steady state value. Then, in the power-off cycle, high energy electrons are quickly lost due to inelastic collisions and rapid diffusion losses to the wall. In these systems, f(ε) can be controlled through choice of the pulse repetition frequency (PRF) and duty cycle as these determine the relative role of thermalization. As a result, the fluxes to the wafer can also be controlled with these parameters. Hence, the etch properties during pulsed-operation may be controllably different than with continuous wave (CW) excited plasma. In this presentation, the f(ε), ratios of fluxes to the wafer and etch properties in pulsed capacitively coupled plasmas (CCP) will be discussed with results from a 2-dimensional plasma hydrodynamics model. The simulation is performed separately on two scales the reactor scale which produces f(ε) and fluxes of radicals and ions to the wafer using the Hybrid Plasma Equipment Model (HPEM); and the feature scale which predicts etch profiles simulation using Monte Carlo Feature- Profile Model (MCFPM). The f(ε), fluxes to the wafer and etch properties will be discussed for fluorocarbon gas mixtures etching SiO₂ while varying PRF and duty cycle at different pressures during pulsed operation. Comparisons will be made to CW operation.