Langmuir Probe Measurements in the Gaseous Electronics Conference Rf Reference Cell

Abstract

The use of a Langmuir probe system in two GEC cells is reviewed. The major problems associated with probe diagnostics in a GEC cell are outlined and discussed. While the data base is still insufficient to give definitive values for many parameters, a number of standard measurements are put forward. The plasma density in argon is 9×109 cm−3 (±20 %) at an applied rf voltage of 250 V (500 V peak to peak) and a gas pressure of 13.3 Pa (100 mTorr). The electron density scales linearly with applied voltage. The plasma to ground sheath resistance is shown to be very important with a value of 810 Ω in argon at a pressure of 13.3 Pa (100 mTorr) and discharge current of 0.1 A. The value of plasma to ground resistance scales inversely with discharge current and sublinear with pressure. Two standard features in the electron energy distribution function (EEDF) have been proposed as a test of the ability of a probe system to resolve features, first, the transition from a low temperature (<1 eV) bi-Maxwellian distribution to a Druyveysten distribution (3 eV) at 13.3 Pa (100 mTorr) in argon, and the “hole” in the EEDF at 2 eV to 4 eV in nitrogen plasmas.

Observations of bi-Maxwellian and single Maxwellian electron energy distribution functions in a capacitively coupled radio-frequency plasmas by laser Thomson scattering

“…Similar results and conclusions have been obtained by other groups. [4][5][6][7][8] The bi-Maxwellian eedf also has been obtained during computer simulation and modeling studies of capacitively coupled rf discharges in argon and other gases. [9][10][11][12] Godyak and co-workers have stated that the limitations of the energy resolution and range of Langmuir probes make determination of low-energy electrons and detection of relatively high-energy electron tails difficult for some discharge conditions.…”

Use of particle-in-cell simulations to improve the actinometry technique for determination of absolute atomic oxygen density

“…Much effort has been focussed on the development of non-invasive plasma diagnostics for industrial plasmas to enable monitoring of the plasma composition and conditions within the plasma chamber without disturbing the process. Traditional plasma probes such as Langmuir probes which are used to measure electrical characteristics and charged species densities in plasma [7], or catalytic probes which are used to measure atomic O densities [8,9] are commonly used in research plasma sources to characterise the plasma. However, these are invasive probes and so are undesirable in a manufacturing environment as the probe can disturb the plasma and also possibly introduce contaminants into the process chamber which can deposit onto the wafer and impact the operation of the final product in a negative manner.…”

Detection of chamber conditioning by CF4 plasmas in an inductively coupled plasma reactor

“…First, an argon plasma is used as a base case reference condition. 12,15,16 It may be the case that some conditioning of this nature has occurred here, however, the effect is not very strong. Thus, an argon plasma is run at 30 mTorr pressure and 200 W coil power for approximately 3 h ͑enough time for it to reach steady state͒ to diagnose the state of the chamber.…”