Study of the effects of neutral gas heating in a radio frequency inductively coupled plasma / Kanesh Kumar Jayapalan

摘要

A 13.56 MHz, planar coil, inductively coupled plasma reactor was experimentallyudand theoretically characterized; with emphasis on the effects of neutral gas heating onudthe distribution of the H mode magnetic fields of the source coil and the E-H modeudtransition characteristics of the discharge.udThe radially resolved electron density, ne, electron temperature, Te and electronudenergy distribution function (EEDF) were measured using a Langmuir probe at differentudaxial distances above the dielectric plate for 0.03, 0.07 and 0.2 mbar argon pressures.udThe range of ne and Te obtained were (0.065 ± 0.004)-(4.0 ± 0.6) × 1017 m-3 andud(1.38 ± 0.08)-(3.8 ± 0.2) eV assuming Maxwellian distribution. The measured neuddistribution at 0.2 mbar suggested significant influence of neutral gas heating. EEDFudplots showed that the distributions were Maxwellian-like.udThe radially resolved absolute axial magnetic field, |Bz|, and absolute radial magneticudfields, |Br|, were measured using electrostatically compensated magnetic probes in theudappropriate orientations. The fields were measured at different axial distances above theuddielectric plate for the chamber in evacuated condition and for 0.03, 0.07 and 0.2 mbarudargon pressures. R.f. power was set at 180 W. Maximum |Bz| and |Br| fields wereudobtained when the chamber was in evacuated condition with values of (1.507 ± 0.005) ×ud10-4 T and (7.67 ± 0.01) × 10-5 T, respectively.udThe peak E-H mode transition current, Itr and peak H-E mode transition current, Imtudwere measured using a current probe for 0.02-0.2 mbar argon pressures. The minimumudvalue for Itr was (13.5 ± 0.5) A at 0.08 mbar, whereas, the minimum value for Imt wasud(8.3 ± 0.1) A at 0.3 mbar. As pressure is increased, hysteresis between E-H mode andudH-E mode transitions was observed to become more distinct. The line averaged neutral gas temperature, Tn, was measured using a fiber probe withudthe actinometry optical emission spectroscopy (AOES) technique at 0.03, 0.05, 0.07, 0.1udand 0.2 mbar argon pressure for different axial distances above the dielectric plate. R.f.udpower was varied from 100 W to 200 W. The range of Tn obtained wasud(350 ± 30)-(840 ± 30) K.udFor theoretical characterization, two predictive models were used. The first was anudelectromagnetic field model that simulates |Bz| and |Br|, using empirically fitted,udspatially resolved electron density, ne (r, z) and electron temperature, Te (r, z).udSimulations were run for spatially averaged Tn and heuristically fitted, spatiallyuddistributed temperature, Tn (r, z). Tn (r, z) gave the closest agreement to the measuredudmagnetic fields.udThe second model was a power deposition model that simulates Itr and Imt.udSimulations were run for Tn = 300 K and at elevated Tn. Calculations better matched theudmeasured values only when neutral gas heating was considered. The effect of hysteresisudin mode transition of the discharge was also demonstrated using a fitted 3D powerudevolution plot.udThese results indicate that neutral gas heating plays an important role in influencingudplasma parameters. Thus, knowledge of the effects of neutral gas heating is essential inudproviding better understanding of the formation and maintenance of the plasmauddischarge.