| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuM |
| Session: | Plasma Diagnostics, Sensors and Control |
| Presenter: | Tyler List, University of Houston |
| Authors: | T. List, University of Houston T. Mu, University of Houston V.M. Donnelly, University of Houston D.J. Economou, University of Houston |
| Correspondent: | Click to Email |
As the requirements for plasma etching become more stringent, the need for plasmas that can produce monoenergetic ion energy distributions (IED) keeps increasing. The problem of charging inside of insulating features also becomes magnified at smaller feature sizes, which result in higher aspect ratios. A process in which electrons can reach and neutralize charged features is important to creating nearly monoenergetic IEDs. An argon RF pulsed plasma with synchronous DC boundary voltage was used to generate a nearly monoenergetic IED. To minimize charging of insulating surfaces, short positive voltage pulses were applied to the chuck holding the substrate during the afterglow, capacitively-coupling to the substrate surface and causing electrons to reach the surface and neutralize the surface charge. This allows a self-limited, nearly grounded surface potential to be achieved. Consequently, positive ions can reach the surface without slowing down by positive surface charge. The ion energy therefore is equal to and controlled by the plasma potential relative to ground, set by a synchronous bias voltage in the afterglow of the pulsed plasma. Surface potential measurements confirmed that DC chuck pulses temporarily neutralize the surface charge. Retarding field energy analyzer measurements performed on the floating chuck with the pulsed plasma and no boundary bias or chuck bias pulses showed an IED with a large very low energy peak (~0-2 eV) and a low energy peak (~10 eV, depending on pressure), corresponding to the power off and power on portions of the cycle, respectively. When the boundary bias and chuck pulses are applied in the afterglow, these peaks change slightly and a third peak appears at an energy near that of the boundary bias voltage. Analysis of the passive charging rate on the surface allowed the prediction of optimal pulsing frequency. Careful tuning of the other chuck pulsing width and amplitude, as well as the pulsed plasma parameters, also improves control of the IED.