Diagnostics of low-frequency CH4and H2discharge by optical emission spectroscopy

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Abstract
Low-frequency glow discharge for the deposition of hydrogenated amorphous carbon has been investigated by using time- and space-resolved emission spectroscopy as the parameters of pressure (0.34 and H2 at 100 kHz and 10 SCCM. The authors ascertain the temporal structure of the discharge. The CH(B2 Sigma -; v'=0 to X2 Pi ; v"=0) band head in CH4/H2 is selected as a probe for monitoring the dynamics of the electron transport. The Ar I (3p55p:3p1 to 3p54s:1s2) line in pure Ar is also observed for comparison with the discharge structure in CH4/H2. The glow discharge property changes significantly with total gas pressure in the CH4/H2 mixture under investigation. Considerable variation is observed between the sustaining voltage and the emission profile of the discharge with the increase of mixture ratio of CH4 to H2 at constant power. Remarkable differences in the emission profile exist between CH4/H2 and Ar. The authors show that the drift velocity of the dominant ions plays an important role in deciding the structure of the discharge especially at low frequency, and that the plasma bulk potential in Ar is higher than that in H2 at the same applied voltage.