Study of spatial profiles of capacitively coupled VHF H₂ plasma by simulation

The spatial profiles of a VHF H₂ plasma (60MHz) for different discharge gap distances were examined at pressures of 66.7 and 133.3 Pa by twodimensional simulations using the plasma hybrid code. The electron density had a peak profile, and the maximum density depended on both the discharge gap distance and the pressure. A high-electron-density plasma with a low-electron temperature of approximately 1 eV was predicted by simulation at discharge gap distances of 15 and 20 mm. The plasma potential profile was composed of a plateau at the center and sharp slopes at the two sides. The axial profiles of the H⁺, H₂⁺, and H₃⁺ densities were calculated for the discharge gap distances of 10, 15, and 20 mm. It was found that the dominant ion species was H₃⁺ except near the discharge electrode and the H₂⁺ density near the discharge electrode was not negligible compared with the H₃⁺ density at 66.7 Pa.