Kazuya Nagaseki

Mass Spectrometry of Discharge Products at 13.56 MHz in SF6 Gas

Discharge products in SF6 RF plasma were measured by means of direct sampling using a quadrupole mass spectrometer. In the plasma, the neutral dissociative species SF2 and SF4 are present. The positive ion SF3+ is predominant, and SF5+, SF2+, SF+ and F+ are also present. The concentration of each neutral and ion product depends on RF power, gas flow rate and area of the silicon wafer set on the grounded electrode. When SF, SF2, SF+ and SF2+ increase to certain amounts, S2F+, SF2+ and S+ can be observed.

Ionic Species in 13.56 MHz Discharges in CF 4 Gas and Mixtures of It with Ar and O 2

Signal intensities of positive ions were measured in situ by direct sampling from parallel-plate discharges in CF 4 /Ar and CF 4 /O 2 mixtures using a quadrupole mass spectrometer. Major positive ions in CF 4 /Ar discharge are CF x + (x = 3, 2, 1) and Ar + . Some of the production of CF 2 + and CF + is considered to be due to the contribution of Ar + . Major positive ions in CF 4 /O 2 discharge are CF 3 + , O y + and F y + (y = 2, 1). The signal intensity of CO 2 + is of the same order as that of F y + . The signal intensities of F y + and O + in CF 4 /O 2 discharge are higher than those in pure CF 4 and O 2 discharges, respectively. Intensity ratios of the ions vary with the gas mixing ratios.

Positive Ions in C 4F 8 RF Discharge in a Planar Diode

Positive ions were measured in situ by direct sampling from C4F8 discharge at 13.56 MHz using a quadrupole mass spectrometer. Major positive ions in the discharge plasma are CF+, CF2+, CF3+, C2F4+, C2F5+ and C3F5+. When the gas flow rate increases, the signal intensity of C2F4+ increases. The intensity variation of C3F5+ is similar to that of C2F4+. However, those of CF3+ and C2F5+ decrease with increasing gas flow rate, and those of CF+ and CF2+ are almost constant. The difference in intensity variations is considered to result from the production processes of ions.

Positive and negative ions in RF plasmas of SF6/N2and SF6/Ar mixtures in a planar diode

Ionic species in 13.56 MHz discharge of SF6/N2 and SF6/Ar mixtures were measured by means of direct sampling using a quadrupole mass spectrometer. Dominant negative ions in the SF6/N2 discharge are F-, SF5- and SF6-, while the positive ions are SF3+, SF5+ and N2+. In the SF6/Ar discharge the major ions are the same as in the SF6/N2 discharge except that N2+ is replaced by Ar+. The signal intensity ratios of these ionic species depend on the ratio of N2 or Ar to SF6 in the discharge. In particular, the ratio of Ar to SF6 in the SF6/Ar discharge increases, the signal intensity ratio of SF3+ to SF5+ shows a concave variation, and the total intensity of negative ions decreases rapidly in the SF6/Ar discharge. These results in the SF6/Ar discharge are different from the variations in the SF6/N2 discharge, and seem to be based on the effects of the metastable atom Ar* on both production of SF3+ and extinction of negative ions.

Positive Ions in RF Discharge Plasma of CF_4 Gas in a Planar Diode

Positive ions were measured in situ by direct sampling from CF4 discharge space at 13.56 MHz using a quadrupole mass spectrometer. CF3+ is observed predominantly with smaller amounts of CF2+ and CF+. With increasing RF power, both CF2+ and CF+ shift to the lower energy side of CF3+, and their intensities tend to increase. Such a phenomenon is also observed as controlling the potential of a sampling tip externally. These seem to suggest that CF2+ and CF+ are produced mainly in the sheath region.

Negative Ions in 13.56 MHz Discharge of SF6 Gas in a Planar Diode

Mass spectra of negative ions were measured in situ by direct sampling from SF6 discharges at 13.56 MHz separately in the two cases of the grounded electrode attached with and without Si wafer. In both cases, F- is observed dominantly, with smaller amounts of SF-5 and SF-6. In the case with Si wafer, however, all these intensities decrease overall. Positive ions SF+2 and SF+3 are predominant in the cases with and without Si wafer, respectively. Negative ions SF-2 and SF-3, however, are hardly observed regardless of whether Si wafer is present or not.

Mass spectrometric observation of decomposition products SFx (x=1,2) in SF6 discharge at 13.56 MHz

The presence of a smaller mass fragment SF2 was indicated from the output signal of a quadrupole mass spectrometer by means of direct sampling from an SF6 discharge space at a pressure of 50 or 100 mTorr. Its intensity was observed to increase with the discharge power according to the degree of fragmentation of SF6.

Characteristics of Parallel-Plate RF Discharges in C 4F 8 Gas and C 4F 8/O 2 Mixtures

The discharge characteristics in a range of driving frequencies from 400 kHz to 1 MHz have been investigated by current-voltage measurements and optical emission spectroscopy. At pressures higher than 0.2 Torr, the discharge impedance is resistive, and the intense emission just in front of the instantaneous anode due to the double layer is observed around the phases of ωt=π/2 and 3π/2. These results are similar to those in strong electronegative SF6 discharges. On the other hand, at 0.1 Torr, the discharge impedance is capacitive, and the discharge is of the so-called wave-riding mode. The discharge structure at 1 MHz is scarcely changed by mixing a large amount O2 with C4F8 at a pressure of 0.5 Torr due to the high electronegativity of C4F8.

Floating Potential of a Substance Mounted on Grounded Electrode in 1MHz RF Discharge

RF放 電 を プラズ マプ ロセ シン グに利 用す る場 合に は,電 極面上に物質を置 くことが多い.こ の ような電気 的に浮遊 した物質が どの ように帯電 し,放 電に どのよ う な影響を与えるかを知 ることは応用上必要であ る. 我 々はN2ガ ス低 周波 放電(f≦20kHz)に お いて, 電極面上の電気的浮遊物質に よる発光 の時間空間変 化な どの放電特性への影響 と浮遊電位 の時間的変化の関係を 明 らかに した1).今 回は,1MHz RF放 電 において接地 電極面上に電気的に浮遊す るよ うに物質 を取 り付けた場 合の,物 質の浮遊電位,放 電電圧電流を測定 し,物 質の 帯電 が放電に与える影響 の有無を調べた.ま た,電 極間 中央 に挿入 した プローブの電位変動を測定 し,物 質の浮 遊 電位変動 と比較 し検 討 した.実 験は電気 的に負性 な SF6ガ ス,負 性 の無 いN2ガ ス,SF6-N2混 合 ガス(SF6 5~10%)を 用 い て行 った.放 電条 件 は圧 力0.05~0.5 Torr,電 力0.8~3.0Wで ある.本 報 では これ らの結果 につ いて報告する.