Fumiyoshi Tochikubo

Study of the structure in rf glow discharges in SiH4/H2 by spatiotemporal optical emission spectroscopy: Influence of negative ions

Radio frequency glow discharges in SiH4(50%)/H2 at 13.56 MHz and 100 kHz have been investigated by using time‐ and space‐resolved optical emission spectroscopy. The relative net‐excitation rate is obtained by deconvolving the spatiotemporal emission profile considering the influence of the radiative lifetime. From the results, we infer the behavior of electrons with energy greater than the threshold energy for the dissociative excitation and we discuss the discharge structure. Lines of SiI(4s 11P0→3p 21D), SiH(A2Δ;v’=0→X2Π;v‘=0), Hα, and H2(d 3Πu→a 3Σ+g) are selected for observation. It is concluded that there exists a considerable population of negative ions compared with positive ions, which has not been previously proposed in high‐frequency discharges in SiH4 because of the small degree of electron attachment. At 13.56 MHz, the optical emission oscillates at 2ω in the bulk plasma region, in addition to the emissions at the plasma‐sheath boundaries. It implies that the field in the bulk is strengthened ...

Spatiotemporal optical emission spectroscopy of rf discharges in SF6

Space‐ and time‐resolved emission spectroscopy was applied to obtain information on the kinetics of radio‐frequency (rf) discharges for 100 kHz, 800 kHz, and 13.56 MHz in SF6. Emission lines of fluorine and SFx radical were used, but particularly useful were the second positive (2+) and the first negative (1−) bands of nitrogen. The two nitrogen bands gave an opportunity to separate, respectively, the behavior of middle‐energy (11–20 eV) and higher‐energy (above 20 eV) electrons. Development of double layers was studied from the excess emission close to the anode due to an increased electric field. Also observed were the emission from the bulk and emission due to the electrons accelerated in the instantaneous cathode sheath. The development of these features was followed as a function of the pressure, frequency, and power.

Investigation of the high-frequency glow discharge in Ar at 13.56 MHz by spatiotemporal optical emission spectroscopy

The radio frequency glow discharge in Ar at 13.56 MHz has been investigated by using time- and space-resolved emission spectroscopy with a resolution of 0.2 ns. The relative net excitation rate is also obtained by deconvoluting the emission profile considering the effect of the lifetime. From these results, the authors are able to guess the electron transport and the temporal structure of the discharge. ArI(3p5 to 1s4), ArI(2p2 to 1s5) and ArII(4p4D7/2 to 4s4P5/2) lines are selected for observation. The electrons with low energy, epsilon >14.57 eV, are transported corresponding to the phase of the current. The electrons with higher energy, M>35.05 eV, are observed at the phase corresponding to the applied voltage only when the aluminium electrode is used under the present experimental conditions. It is confirmed that the high-energy electrons are secondary electrons emitted from the electrode. The RF discharge in Ar at 13.56 MHz has two modes with a hysteresis loop as the function of input energy.

Study of the structure of radio frequency glow discharges in CH4 and H2 by spatiotemporal optical emission spectroscopy

Radio frequency discharges at 13.56 MHz in CH4(100%), CH4(10%)/H2, and H2(100%) are investigated by time‐ and space‐resolved optical emission spectroscopy. The spatiotemporal net‐excitation profile of H(n=3) is presented and discussed. The absolute value of the net‐excitation rate, the emission intensity, and the density of the optically allowed electronic excited species are also measured. The self‐quenching rate of H(n=3) and CH(A) by H2 and CH4 are estimated and compared with the previous works. The importance of the quenching of CH(A) by atomic hydrogen is also discussed. Excitation by very high‐energy electrons is shown from the difference of the emission profile between Hα and H2(d3Πu→a3Σg+) in H2 at 100 kHz.

Diagnostics of high‐frequency discharges in CH4/H2 by time‐ and space‐resolved optical emission spectroscopy

The diagnostic technique of the rf glow discharge at 13.56 MHz is developed by using the spatiotemporally resolved optical emission spectroscopy. New experimental evidence that the temporal excitation rate at the sheath peaks in phase with the maximum of the total current is obtained in a parallel‐plate geometry at 13.56 MHz in CH4(10%)/H2 under a typical condition of the plasma chemical vapor deposition of amorphous carbon film at room temperature.

Frequency dependence on the structure of radio frequency glow discharges in Ar

The frequency dependence of the sustaining voltage in a radio frequency discharge has been investigated under minimum sustaining and constant power conditions in Ar. In addition to the well‐known feature that the sustaining voltage is high at low frequency and low at high frequency, the difference between monoatomic and polyatomic gases is recognized. The phase shift between voltage and current at 1 Torr decreases with increasing frequency above 500 kHz. This results from the electron density modulation having a delay with respect to the applied voltage. The phase shift at high frequency increases with increasing applied voltage, due to the balance of drift and diffusion fluxes of electron. The spatiotemporal net excitation rate of Ar(3p5) was measured at 100 kHz, and 4 MHz, and 13.56 MHz. It is reconfirmed that the sustaining mechanism of the discharge at low frequency is ionization by secondary electrons from the electrode, while at high frequency it is ionization due to reflected electrons by the oscil...

Influence of frequency, pressure, and mixture ratio of electronegative gas on electrical characteristics of rf discharges in N2‐SF6 mixtures

Electrical characteristics of rf discharges in SF6 and in its mixtures with N2 were experimentally investigated. In addition space‐ and time‐resolved emission spectroscopy was used to gain a better understanding of kinetics of processes leading to various observed characteristics. A complicated dependence of minimum sustaining voltage on frequency was observed with a peak at 3 MHz. It was explained as the result of transition from the conditions where discharge is sustained by ionization in the bulk and the double‐layer region to the conditions where secondary electron yield makes a large contribution. Another possible explanation is the one invoking transition from the conditions where at high‐frequency double layer is formed by electron modulation to the condition where a double layer is formed by positive and negative ions. In voltage‐current dependencies at 13 MHz two distinct regions were observed similar to the α to γ transitions observed for electropositive gases. Ionization by secondary electrons,...

Absolute measurement of the excitation rate and density of the excited species in an RF discharge from optical emission spectroscopy

A simple method of ray tracing is adopted to calibrate the absolute value of the net production rate by electron impact of excited species with short radiative lifetime in a discharge. As an example, the net excitation rate and density of Ar(3p5) are measured in the RF glow discharge at 13.56 MHz, 1 Torr in Ar.

Study of the Electron Transport in an RF Discharge in Ar and CH4/H2by Optical Emission Spectroscopy

There are many theoretical and experimental studies of an electron swarm in a DC field. The time behavior of electron transport in an RF field is also studied from the Boltzmann equation (Winkler et al., 1985; Makabe and Goto, 1988). But we have few information about the electron transport in an RF discharge plasma, which is mainly used for plasma processing, because of the existence of the sheath and bulk region.