| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS-WeM |
| Session: | Plasma Surface Interactions (Fundamentals & Applications) I |
| Presenter: | H. Shin, University of Houston |
| Authors: | H. Shin, University of Houston W. Zhu, University of Houston X. Lin, University of Houston V.M. Donnelly, University of Houston D.J. Economou, University of Houston |
| Correspondent: | Click to Email |
A novel dual-source inductively coupled plasma (ICP) system was designed and built to control the electron energy distribution function (EEDF) in the plasma, and the ion energy distribution (IED) on the substrate. The main ICP source has a Faraday shield to minimize the RF component of the plasma potential. The substrate electrode, as well as a “boundary” electrode in contact with the plasma, can be independently biased by DC or RF voltages, of the desired waveform, to influence the IED. A secondary tandem ICP source can inject plasma, radicals or metastable atoms to the main ICP to influence the EEDF. The main ICP source was characterized using a Langmuir probe (LP), trace rare gas optical emission spectroscopy (TRG-OES), and an electrostatic ion energy analyzer. Emphasis was placed on pulsed plasma operation to achieve better control of the IED (as well as the ion angular distribution). With the Faraday shield installed, the plasma potential was several volts lower, and the peak-to-peak RF voltage of the plasma potential was suppressed to 1-2 V, as compared to the case without Faraday shield, allowing for smaller spread of the IED. The plasma potential, and thus the peak of the IED could be precisely controlled by the voltage applied to the boundary electrode. Accurate control of the ion energy and width of the IED is important for processes such as atomic layer etching, for which the threshold energies between etching and sputtering differ by only several volts. During the OFF period of a square wave modulation of the plasma power (50 μs ON, 50 μs OFF), the electron temperature decayed from 3.1 eV to less than 0.25 eV, with only a 20 % drop in plasma density for a 10 mtorr pressure, 200 W (average) power argon plasma. Time resolved EEDFs were also measured by the LP and compared to those extracted from TRG-OES experiments during the ON and first few ms of the OFF time. Tailored voltage waveforms were used to obtain “designer” ion energy distributions on the substrate. Finally, results for other gases (such as krypton and oxygen) will be discussed and compared to those obtained for argon plasmas.
Work supported by the DoE Plasma Science Center and NSF