Mass spectrometric studies of low pressure CH4, CH4/H2, and H2 plasma beams generated by an inductively coupled radio frequency discharge

Low pressure CH4, CH4 /H-2, and H-2 plasma beams were generated by a 13.56 MHz inductively coupled radio frequency (rf) plasma with a magnetic field (similar to300 G) to utilize them as radical sources for the epitaxial growth of diamond. The threshold ionization technique using a quadrupole mass spectrometer has been employed to measure the absolute density of CH3 radicals (n) in CH4 and CH4 /H-2 plasma beams. The ions of CH4 and CH4 /H-2 plasma beams were composed of CHx, C2Hx, C3Hx, and H-x fragment ions, while H-x fragment ions occupied the H-2 plasma beam. When the rf power and the pressure were increased, the it and the relative intensities of H-3(+), C2Hx, and C3Hx fragment ions were increased. This implies that both the homogeneous secondary ion-molecular reactions and the heterogeneous plasma-surface interactions take place in the plasma generation region of the low pressure plasma beams with an increase in rf power and pressure. The increase of H-3(+) also induces an increase of atomic hydrogen, which is essential for diamond growth. It is therefore concluded that moderate rf power and higher pressure are favorable for diamond growth. (C) 2002 American Vacuum Society.