K.C. Paul, M. Takahashi, S. Hatazawa, and T. Sakuta

Department of Electrical and Computer Engineering, Kanazawa University
Kodatsuno 2-40-20, Kanazawa 920, Japan
9030paul@ec.t.kanazawa-u.ac.jp

Like the importance of hydride generation for arsenic study in groundwater and so on, nitride generation would be attractive for different purposes including film fabrication. Electronegative SF6 gas absorbs electron in plasma and could play substantial role in plasma processing, where lowering of electron density or electrical conductivity is the objective. Over the last decades, considerable effort has been made to study the behavior of SF6 in circuit-breaker environment, where the flow is transient at high pressures (0.5 Mpa); highly turbulent; and there is little process control. Recently, due to the environmental concerns, a replacement for SF6 in circuit breakers is sought. Nitrogen or N2/SF6 mixture appears to be a good candidate for such purpose. For all these circumstances, study of SF6 and N2 plasmas find significant importance and momentum.

In this paper, we report on successful generation of Ar, SF6, and N2 radio-frequency (rf) inductively coupled plasmas (ICPs) at atmospheric pressure for an 82 mm inner diameter torch and on spectroscopic measured results. Please note that SF6 and N2 ICPs are of mixed-gas type; here Ar ICP was generated first whereinto SF6 or N2 was injected. 225 slpm total flow rate was maintained for all ICPs. In addition, numerical results are also reported for these ICPs at similar operating conditions by sloving a 2-dimensional and axisymmetric ICP model [1]. The ICPs were assumed to be under local thermodynamic equilibrium and optically thin.

In order to determine the radial distribution of spectral intensity, the plasma was scanned along the torch diameter at a certain axial position, where 64 addresses were stored at regular interval of the 82 mm torch diameter. The atomic Ar line intensity, at 842.4 nm wavelength, dropped sharply for SF6 plasma compared to Ar ICP; it took intermediary value for N2 ICP [Fig.1]. This profound drop of the intensity in SF6 plasma indicates predominant shrinking nature of this type plasma. Between wavelength 350-850 nm, all atomic and ionic spectra were measured. The numerically determined radial temperature profiles confirmed the ample shrinking nature of SF6 ICP as well as moderate contraction of N2 ICP compared to Ar ICP.

[1] K.C. Paul, T. Takashima, and T. Sakuta, `Copper vapor effect on rf inductively coupled SF6 plasmas', IEEE Trans. Plasma Science (in process).