RF discharge with multidipole surface magnetic confinement for low pressure plasma etching

Summary form only given. The development of a plasma source for semiconductor etching which employs permanent magnet multidipole fields is discussed. RF power at 13.56 MHz is applied to a 6-in.-diameter disk electrodes inside the magnet bucket. Langmuir probe measurements of plasma density and electron temperatures, in argon have been performed over operating parameters ranging from 10^-5 torr to 50 mtorr and up to 500 W of RF power. Measurements of self-bias on the powered electrode and RF fluctuations of the floating potential were also obtained for this set of parameters. Preliminary etching results of Si with an Al mask at 3×10^-4 torr in a CF₄/O ₂ gas mixture and 100 W of RF power show anisotropic etch profiles, but low etch rates and some degree of mask erosion. For these conditions in argon. plasma densities of about 7×10⁹ cm ^-3 were observed. Higher densities are needed for higher etch rates, and this can be obtained by either increasing the power level or increasing the pressure. However, the electrode self-bias scales almost linearly with power; thus, increasing the power level can lead to unacceptably high ion bombardment energies. Increasing the operating pressure may help to some degree, but it may be necessary to power the system in a triode arrangement in order to achieve suitable etching conditions