Diagnostic of Surface Wave Plasma for Oxide Etching in Comparison with Inductive RF Plasma

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Abstract
Surface wave plasma (SWP) and inductively coupled plasma (ICP) reactors are high plasma density, unmagnetized sources that show promise for use in next-generation etching processes. We compare the 2.45 GHz SWP with the 13.56 MHz ICP in terms of the radical composition in C4F8/Ar discharges and the electron energy distribution function (EEDF). A comparison of the two plasmas was carefully made in an identical plasma vessel at the same wall temperature where an antenna coupler on a quartz plate was changed from an expanded waveguide for SWP to a loop coil for ICP. Reactive species measurement at the same electron density under the same gas conditions showed marked differences. First, the dissociation degree of C4F8at the same electron density is higher in ICP than in SWP. Second, neutral radical densities (CF3, CF2) at the same electron density are several times higher in SWP than in ICP, and ICP has a high F radical density. Third, as regards ionic composition, ICP contains more Ar+and less fluorocarbon ions (CmFn+), while large molecular ions (C2F4+, C3F3+, C3F5+) exist in SWP. In conclusion, ICP is more dissociative than SWP at the same electron density. This result is tentatively attributed to the difference in the EEDFs of the two plasmas, since optical emission spectroscopy of Ar I suggests 1.5–2 times more high-energy (>14 eV) electrons in ICP than in SWP.