Determination of negative-ion and electron parameters in an Ar/SF6 plasma

Abstract

A new method for evaluating negative ion and electron parameters from the current–voltage characteristics of electric probes is presented. A theoretical model and its related numerical procedures are established and errors included are estimated. Temperatures and densities of negative ions and electrons in a magnetic multipolar-confined plasma of Ar and Ar/SF6 mixtures are determined with allowable errors for various density ratios of the negative ion to the electron.

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

“…The plasma parameters were measured using two Langmuir cylindrical probes: one situated in SP, which has a fixed position and the other in TP, which can be moved in radial direction. The electrical probe circuit and the details of the "Test Function" procedure for extracting the bulk and hot electron densities (n e and n eh ) and temperatures (T e and T eh ) and the negative ion parameters (n ni and T ni ) are presented in detail elsewhere [39,40]. Special care was devoted to avoid recording erroneous probe characteristics affected by contaminations effects reported for reactive plasmas [52,53].…”

“…Negative ion etching with low energies and low charging potentials is also attractive for low damage processing required in node technologies below 50 nm [30]. So far, despite of good theoretical coverage [31][32][33][34][35] and a large variety of methods for negative ion diagnostic including optical emission [36], photodetachment [37], Langmuir probe [38][39][40][41][42][43], thermal probe [44], propagation of the ion acoustic waves [45][46][47] and Thomson scattering [48] there are still important basic questions related to highly electronegative discharges that need to be answered.…”

High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions

“…A similar behavior was previously reported in DC and ICP discharges and it is associated with a depletion of low energetic electrons involved in negative ion formation. 39,41 The uniformity of plasma parameters (V pl , n i , T eff , and n ni /n e ) was investigated by shifting the probe under the magnetic filter for 36 cm, resulting in deviations from center to the edge below 5%, where no special care was considered for tuning the ECR plasma cells in order to further improve the uniformity.…”

“…1(b)) made of permanent magnets (4 mm in diameter, 10 mm in length, and 2000 Gauss at the surface) magnetized on sides and inserted in a 6.33 mm pipe welded in 13 parallel lines situated 25 mm apart is used to reduce the electron temperature, T e , by increasing the diffusion time of electrons from the plasma production region to the processing region. 39 The filter is placed 70 mm below the top plate supporting the plasma cells. The penetration of the magnetic field in plasma volume is negligible (less than 50 Gauss) at a distance larger than 5 cm form the filter.…”

“…The etching rates are estimated using a Veeco V R deck tack profiler. The "test function" method 39,40 in the approximation of bi-Maxwellian electron energy distribution function (EEDF) is used to extract plasma parameters from current-voltage probe characteristics including positive ion, negative ion, bulk electron and hot electron densities (n x ), and temperatures (T x ), where for notation, the subscript x is replaced with i for positive ions, ni for negative ions, eb for bulk electrons, and eh for hot electrons. 41 The total electron density, n e , is defined as n e ¼ n eb þ n eh .…”