| Research Abstract |
The main results of the research were focused on the followings objectives : to understand the mechanism of a film growth in plasma and in a plasma-assisted laser ablation system and to understand the influence of the deposited film on the spectroscopic and electrical characteristics of plasma. Finally we can control the film properties during the deposition process.
(A)Dielectric barrier discharge (DBD) plasma in CH_4 and Ar gas mixtures used for a-C:H film deposition
1.Spectroscopic and electrical properties of DBD
In plasma, we measured Ar(1s_5), Ar(1s_3) and Ar(1s_2) atoms number density using a plasma modulation laser absorption spectroscopy coupled with laser absorption spectroscopy system. The CH(X^2Π) radical number density was measured using optical emission spectroscopy and actinometry method. The excitation transfer from Ar(1s_5) and Ar(1s_3) metastable atom to CH(A^2Δ) radical, which was induced by collisions in plasma, was observed by laser collisional induced fluorescence. A
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r(1s_5) metastable atoms in the vicinity of about 300nm of the film surface were detected by using evanescent wave absorption spectroscopy method.
The electrical properties of DBD were measured using V-Q Lissajous figures. The effective gas breakdown voltage, the electncal charge discharged through the gas in half cycle and the energy deposited in full cycle, characterized DBD plasma.
2.Film analysis
The contents of sp^3,sp^2 bonds and CH_2,CH_3 groups in the a-C:H film were determined by using Fourier Transform Infra Red (FTIR) spectroscopy. The content of hydrogen in the film was calculated from the IR absorption spectrum. The refractive index, the extinction coefficient and the thickness of the a-C:H film were determined using spectroscopic ellipsometry method. The energy gap of the film was calculated from the extinction coefficient of a-C:H film The maximum value of the energy band gap, which corresponds to a high content of sp^3 fraction in the film, was obtained when CH radical number density in the plasma was minimum (〜10^8cm^<-3>).
(B)RF plasma-assisted laser ablation of carbon in nitrogen atmosphere
The spatial distributions of C and N atoms were measured by time-resolved absorption spectroscopy. The spatial distributions of the relative densities of CN radical, C_2, and C_3 molecules were measured using time-resolved emission spectroscopy. We determined that nitrogen gas produced an increase of carbon atoms and molecules densities in the ablation plume. It was observed that addition of RF plasma to the plume increased the CN radical and C atom densities and decreased the C_2 and C_3 molecule densities.
The RF plasma changed the evolution of various fractional species of C,N,CN,C_2 and C_3 in the ablation plume. The chemical reactions with and without RF plasma were explained using the evolution and the density of the fractional species of C,N,CN,C_2 and C_3 in the plume. Film properties depend on the composition of the laser ablation plume. Less
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