AVS 45th International Symposium
    Manufacturing Science and Technology Group Thursday Sessions
       Session MS-ThM

Paper MS-ThM11
Simulations of the Performance of Novel Ion Current Sensors

Thursday, November 5, 1998, 11:40 am, Room 317

Session: Sensors and Support Technology
Presenter: M.A. Sobolewski, National Institute of Standards and Technology
Correspondent: Click to Email
To obtain optimal results from plasma processing, the properties of ions and neutrals incident on the substrate must be carefully controlled. If sensors for the relevant properties of the ions and neutrals were available, they could be used to detect process drift and equipment malfunctions, diagnose their origin, and take correction action, if needed. One particularly important parameter to monitor is the total ion current at the substrate. Recently, a method has been demonstrated for using external, radio-frequency (rf) electrical measurements to monitor the ion current at an electrically insulating or conducting wafer during processing by a high-density plasma.@footnote 1@ The rf signals are generated by the rf bias power which is normally applied to wafers. There is no need for any probe to be inserted into the reactor or for any additional power supplies which might perturb the plasma. At low rf bias frequencies (0.1-1 MHz) ion currents measured by this technique agree well with dc measurements of the ion current, but they agree less well at higher frequencies.@footnote 1@ In this work, this disagreement was investigated using a fluid model of the sheath region of high-density plasmas. Simulations show that, as the rf frequency approaches the ion plasma frequency at the edge of the sheath, the ion current at the electrode varies strongly with time during each rf period. Under these conditions, the rf measurement of ion current differs from the time-averaged value of the ion current. The simulations are used to characterize the error in the rf measurement technique and to suggest new rf methods which more accurately determine the time-averaged ion current. @FootnoteText@ @footnote 1@M. A. Sobolewski, Appl. Phys. Lett. 72, 1146 (1998).