Characterization of 100 MHz inductively coupled plasma (ICP) by comparisonwith 13.56 MHz ICP

The effect of the excitation frequency on the dissociative process of the C 4F8 gas was]investigated by comparing a 100-MHz [very high-frequency (VHF)I inductively coupled plasma (ICP) with a 13.56 MHz [radio frequency (rf)] I CP. The same apparatus except for the wave generator and matching network w as used for both ICPs in order to investigate the frequency effect as preci sely as possible. The electron density and electron temperature in an Ar pl asma were measured by using a Langmuir probe. From the dependence of the ra dial distribution of the Ne on-the ICP source power, it was found that the rf ICP was produced in a cylindrical space under the coil area, while the V HF ICP was generated throughout the reactor. In C4F8/Ar plasma, the CFx (x = 1, 2, 3) radical densities near the reactor wall were measured by using a ppearance mass spectrometry, and-the F radical density was measured by usin g actinometry through the optical emission spectroscopy of Ar (750.4 nm) an d F (703.7 nm). The degree of dissociation of the C4F8 in the VHF ICP was h igher than that in the rf ICP, but the CF2/F density ratio in the VHF ICP w as 3-5 times that in the rf ICP. This result indicates that the dissociatio n of high-molecule gases, including C4F8, proceeds more easily in the VHF I CP than in rf ICP and that there is much less dissociation of high-order ra dicals (e.g., CF2+e-->CF+F+e) in VHF ICP than there is in rf ICP. Hence, VH F ICP suppresses F radical generation better than rf ICP. (C) 1999 American Vacuum Society. [S0734-2101(99)09504-4].