| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS-TuM |
| Session: | Plasma Diagnostics and Sources I |
| Presenter: | Hanyang Li, University of Houston |
| Authors: | H. Li, University of Houston Y. Zhou, University of Houston V.M. Donnelly, University of Houston J. Chiu, MKS Plasma & Reactive Gas Solutions X. Chen, MKS Plasma & Reactive Gas Solutions |
| Correspondent: | Click to Email |
Remote plasma sources are widely used in many applications, such as chamber cleaning and flowable chemical vapor deposition (FCVD). Processes using remote plasmas are purely chemical in nature, since there are no ions present. In such processes, it is desirable that the dissociation rate of the feed gases in the plasma source be as high as possible, while recombination rates of reactive species on the way to a downstream chamber should be minimized. Only a few studies have been reported on low frequency, high pressure, very high density remote plasma sources. In this paper we present results on radical densities and gas dissociation fractions for a 400 kHz toroidal transformer-coupled plasma source (MKS Instruments), operating at a power density of 5 – 50 W/cm3 with feed gases mixtures of O2 or NF3 with Ar, and pressures of 0.4 or 2.0 Torr. The radical densities and feed gas dissociation percentages in the plasma were measured by optical emission spectroscopy (OES), combined with Ar actinometry. Plasma products flow into an anodized Al downstream chamber that is probed by vacuum ultraviolet (VUV) absorption spectroscopy and line-of-sight molecular beam mass spectrometry, allowing radical and stable species number densities to be determined in the plasma source as well as in the downstream chamber. The dissociation of O2 and NF3 was found to be roughly from 60% to 10% with the rise O2% in plasma and >95% in the plasma source (via Ar actinometry with O and F) and not very dependent of flow rate. Midway across the downstream chamber, substantial recombination of O to form O2 (via VUV O2 absorption) occurred; the O/O2 ratio was a strongly increasing function of increasing flow rate. At the back wall of the downstream chamber, O has nearly completely recombined to O2 (mass spectrometry), even at the highest flow rate. NF3 is completely dissociated and does not reform in the downstream chamber; no NF or NF2 was detected. F was found to be mostly recombined to for F2 at the back of the downstream chamber. The F2, F and N2 product absolute number densities confirmed the 3:1 F:N mass balance of the NF3 feed gas. The gas temperature at the back downstream chamber was also measured by mass spectrometry, and was found to be 450K for 95% NF3/Ar at a flow rate from 200 sccm to 600 sccm and 2.0 Torr.