G. A. Hebner

An inductively coupled plasma source for the Gaseous Electronics Conference RF Reference Cell

In order to extend the operating range of the GEC RF Reference Cell, we developed an inductively coupled plasma source that replaced the standard parallel-plate upper-electrode assembly. Voltage and current probes, Langmuir probes, and an 80 GHz interferometer provided information on plasmas formed in argon, chlorine, and nitrogen at pressures from 0.1 Pa to 3 Pa. For powers deposited in the plasma from 20 W to 300 W, the source produced peak electron densities between 1010/cm3 and 1012/cm3 and electron temperatures near 4 eV. The electron density peaked on axis with typical full-width at half maximum of 7 cm to 9 cm. Discharges in chlorine and nitrogen had bimodal operation that was clearly evident from optical emission intensity. A dim mode occurred at low power and a bright mode at high power. The transition between modes had hysteresis. After many hours of high-power operation, films formed on electrodes and walls of one Cell. These deposits affected the dim-to-bright mode transition, and also apparently caused generation of hot electrons and increased the plasma potential.

Spatially resolved, excited state densities and neutral and ion temperatures in inductively coupled argon plasmas

Spatially resolved, line integrated, excited state densities, and neutral and ion temperatures have been measured in inductively coupled argon plasmas. Absorption spectroscopy was used to measure the line integrated density and temperature of the argon 1s5, 1s4, 1s3, and 1s2 energy levels. Laser‐induced fluorescence was used to confirm the neutral temperatures and to measure argon metastable ion temperatures. For rf powers between 50 and 300 W and pressures of 4–50 mTorr, the line integrated density of the 1s5 energy level varied between 1×1016 and 2×1016 m−2. The densities of the 1s4, 1s3, and 1s2 levels were approximately 4–10 times smaller. In the center of the plasma, the ion and neutral temperatures were identical, between 550 and 1000 K for plasma powers between 30 and 240 W and pressures between 4 and 50 mTorr. The neutral temperature had a maximum in the center of the discharge and decreased towards the edge of the discharge. However, the ion temperature increased to between 3000 and 4000 K at the...

Ion energy and angular distributions in inductively driven radio frequency discharges in chlorine

In this article, we report values of ion energy and angular distributions measured at the grounded electrode of an inductively coupled discharge in chlorine gas. The inductive rf drive in our cell produced high plasma densities (1011/cm3 electron densities) and stable plasma potentials. As a result, ion energy distributions typically consisted of a single peak well separated from zero energy. Mean ion energy varied inversely with pressure, decreasing from 13 to 9 eV as the discharge pressure increased from 20 to 60 mTorr. Half-widths of the ion angular distributions in these experiments varied from 6° to 7.5°, corresponding to transverse energies from 0.13 to 0.21 eV. During the course of the experiment, ion energies gradually decreased, probably due to the buildup of contaminants on the chamber walls. Cell wall temperature also was an important variable, with ion fluxes to the lower electrode increasing and the ion angular distribution narrowing as the cell temperature increased.

Electron and metastable densities in parallel‐plate radio‐frequency discharges

Electron densities were measured in continuous and pulse‐modulated, 13.56‐MHz, helium and argon discharges. These measurements were made in a symmetrically driven Gaseous Electronics Conference Reference Cell. Pulse modulation of the applied potential allowed observation of the time required for the electron density to achieve steady state. In general, helium discharges reached steady state in approximately 1.5 ms, taking three to ten times longer than argon discharges under similar operating conditions. As much as a threefold increase of the electron density was observed in the afterglow of a pulse‐modulated helium discharge, indicative of large metastable densities. Absorption spectroscopy was used to measure the helium singlet and triplet metastable densities throughout the volume of the discharge. For a 1.0‐Torr discharge, helium triplet metastable densities at the center of the discharge were as large as 2.5×1011 cm−3 while the peak singlet density was 3.0×1010 cm−3. The steady‐state electron density...

Frequency dependent plasma characteristics in a capacitively coupled 300 mm wafer plasma processing chamber

Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.

CF, CF2, and SiF densities in inductively driven discharges containing C2F6, C4F8, and CHF3

Laser induced fluorescence was used to measure the spatially resolved CF, CF2, and SiF radical density in inductively driven discharges containing fluorocarbon gases. Measurements of the spatially resolved CF density were performed in C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition on a silicon substrate. In addition, CF rotational temperatures were calculated, assuming saturated spectra. Measurements of the spatially resolved CF2 and SiF density were performed in C4F8, C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition. SiF rotational temperatures were also estimated. As the induction coil power was increased, the SiF density in the center (r=0 cm) increased while the CF2 density decreased and the CF density slightly decreased. In all cases, the radical density in the center of the glow increased with pressure changes from 5 to 30 mTorr while changes in the bias power had little influence on any of the measur...

Negative ion densities in chlorine- and boron trichloride-containing inductively coupled plasmas

The chlorine negative ion density and the electron density in chlorine- and boron trichloride-containing inductively coupled plasmas were investigated experimentally. Measurements were performed in a GEC reference cell operated in the inductively coupled mode. The chlorine negative ion density was measured as an excess electron density produced by photodetachment of electrons from the negative ions by 266 nm radiation from a frequency-quadrupled Nd:YAG laser. Both the excess electron density and the steady-state electron density were measured using a microwave interferometer. Various gas mixtures were investigated including pure Cl2, pure BCl3, combinations of the two, and combinations of these gases with N2 and Ar. Cl− densities up to 4×1011 cm−3 were measured depending on the gas mixture. The ratio of electron density to Cl− density was as high as 3 in Cl2 mixtures, and up to 5 in BCl3 mixtures. The plasma was probed at lower photon energy (355 nm) to photodetach electrons from other potential negative ...

Electron and Negative Ion Densities in C(2)F(6) and CHF(3) Containing Inductively Coupled Discharges

Electron and negative ion densities have been measured in inductively coupled discharges containing C{sub 2}F{sub 6} and CHF{sub 3}. Line integrated electron density was determined using a microwave interferometer, negative ion densities were inferred using laser photodetachment spectroscopy, and electron temperature was determined using a Langmuir probe. For the range of induction powers, pressures and bias power investigated, the electron density peaked at 9 x 10{sup 12} cm{sup -2} (line-integrated) or approximately 9 x 10{sup 11} cm{sup -3}. The negative ion density peaked at approximately 1.3 x 10{sup 11} cm{sup -3}. A maximum in the negative ion density as a function of induction coil power was observed. The maximum is attributed to a power dependent change in the density of one or more of the potential negative ion precursor species since the electron temperature did not depend strongly on power. The variation of photodetachment with laser wavelength indicated that the dominant negative ion was F{sup -}. Measurement of the decay of the negative ion density in the afterglow of a pulse modulated discharge was used to determine the ion-ion recombination rate for CF{sub 4}, C{sub 2}F{sub 6} and CHF{sub 3} discharges.

Negative ion densities in NF3 discharges

This letter shows that the negative ion density in the NF3 discharge is one to two orders of magnitude larger than the electron density. A XeCl laser was used to photodetach the ions and the resultant excess electron population was measured using microwave interferometry.

Behavior of Excited Argon Atoms in Inductively Driven Plasmas

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s5 and 1s4, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s5 level is metastable and the 1s4 level is radiatively coupled to the ground state but is radiation trapped. The argon data are compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rf power and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rf powers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the...