Low pressure argon dual-frequency (DF) capacitively coupled plasma (CCP) is generatedby using different frequency configurations,such as 13.56/2,27/2,41/2,and 60/2 MHz.Characteristics of the plasma are investigated by using a floating double electrical probe and opticalemission spectroscopy (OES).It is shown that in the DF-CCPs,the electron temperatureT_e decreases with the increase in exciting frequency,while the onset of 2 MHz induces a suddenincrease in T_e and the electron density increases basically with the increase in low frequency(LF) power.The intensity of 750.4 nm emission line increases with the LF power in the caseof 13.56/2 MHz,while different tendencies of line intensity with the LF power appear for otherconfigurations.The reason for this is also discussed.
Diamond-like carbon (DLC) films were prepared with CH_4-Ar using a capacitivelycoupled plasma enhanced chemical vapor deposition (CCP-CVD) method driven by dual-frequencyof 41 MHz and 13.56 MHz in combination. Due to a coupling via bulk plasma, the self-bias voltagedepended not only on the radiofrequency (RF) power of the corresponding electrode but also onanother RF power of the counter electrode. The influence of the discharge parameters on thedeposition rate, optical and Raman properties of the deposited films was investigated. The opticalband decreased basically with the increase in the input power of both the low frequency and highfrequency. Raman measurements show that the deposited films have a maximal sp^3 content withan applied negative self-bias voltage of -150 V, while high frequency power causes a continuousincrease in the sp^3 content. The measurement of atomic force microscope (AFM) shows thatthe surface of the deposited films under ion-bombardment becomes smoother than those withnon-intended self-bias voltage.
This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements.Two major processes are considered in this model,electron-impact excitation and the spontaneous radiative decay.The diffusion loss term,which is found to be important for the two metastable states (4s[3/2] 2,4s [1/2] 0),is also taken into account.Behaviours of representative metastable and radiative states are discussed.Two emission lines (located at 696.5 nm and 750.4 nm) are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma.The calculated results agree well with that measured by Langmuir probe,indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.
Nitrogen dual-frequency capacitively coupled plasmas(DF-CCPs) with different frequency configurations,i.e.,60/2 MHz and 60/13.56 MHz,are investigated by means of optical emission spectroscopy(OES) and a floating double probe.The excited nitrogen molecule ion N + 2(B) is monitored by measuring the emission intensity of the(0,0) bandhead of the first negative system(FNS) at 391.44 nm.It is shown that in the discharge with 60/13.56 MHz,the N + 2 emission intensity decreases with the increase in pressure.In the discharge with 60/2 MHz,however,an abnormal enhancement of N + 2 emission at higher pressure is observed when a higher power of 2 MHz is added.Variation in the ion density shows a similar dependence on the gas pressure.This indicates that in the discharge with 60/2 MHz there is a mode transition from the alpha to gamma type when a higher power of 2 MHz is added at high pressures.Combining the measurements using OES and double probe,the influence of low frequency on the discharge is investigated and the excitation route of the N + 2(B) state in the discharge of 60/2 MHz is also discussed.
